| 1. |
- Alizadehheidari, Mohammadreza, 1987, et al.
(författare)
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Nanoconfined Circular and Linear DNA: Equilibrium Conformations and Unfolding Kinetics
- 2015
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 48:3, s. 871-878
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Tidskriftsartikel (refereegranskat)abstract
- Studies of circular DNA confined to nanofluidic channels are relevant both from a fundamental polymer-physics perspective and due to the importance of circular DNA molecules in vivo. We here observe the unfolding of confined DNA from the circular to linear configuration as a light-induced double-strand break occurs, characterize the dynamics, and compare the equilibrium conformational statistics of linear and circular configurations. This is important because it allows us to determine to what extent existing statistical theories describe the extension of confined circular DNA. We find that the ratio of the extensions of confined linear and circular DNA configurations increases as the buffer concentration decreases. The experimental results fall between theoretical predictions for the extended de Gennes regime at weaker confinement and the Odijk regime at stronger confinement. We show that it is possible to directly distinguish between circular and linear DNA molecules by measuring the emission intensity from the DNA. Finally, we determine the rate of unfolding and show that this rate is larger for more confined DNA, possibly reflecting the corresponding larger difference in entropy between the circular and linear configurations.
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| 2. |
- Aronsson, Christopher, et al.
(författare)
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Zinc-Triggered Hierarchical Self-Assembly of Fibrous Helix-Loop-Helix Peptide Superstructures for Controlled Encapsulation and Release
- 2016
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Ingår i: Macromolecules. - : AMER CHEMICAL SOC. - 0024-9297 .- 1520-5835. ; 49:18, s. 6997-7003
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a novel route for hierarchical self-assembly of sub-micrometer-sized peptide superstructures that respond to subtle changes in Zn2+ concentration. The self-assembly process is triggered by a specific folding-dependent coordination of Zn2+ by a de novo designed nonlinear helix-loop-helix peptide, resulting in a propagating fiber formation and formation of spherical superstructures. The superstructures further form larger assemblies that can be completely disassembled upon removal of Zn2+ or degradation of the nonlinear peptide. This flexible and reversible assembly strategy of the superstructures enables facile encapsulation of nanoparticles and drugs that can be released by means of different stimuli.
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| 3. |
- Boye, Susanne, et al.
(författare)
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From 1D Rods to 3D Networks: A Biohybrid Topological Diversity Investigated by Asymmetrical Flow Field-Flow Fractionation
- 2015
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 48:13, s. 4607-4619
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Tidskriftsartikel (refereegranskat)abstract
- Biohybrid structures formed by noncovalent interaction between avidin as a bridging unit and biotinylated glycodendrimers based on poly(propyleneimine) (GD-B) have potential for biomedical application. Therefore, an exact knowledge about molar mass, dispersity, size, shape, and molecular structure is required. Asymmetrical flow field-flow fractionation (AF4) was applied to separate pure and assembled macromolecules according to their diffusion coefficients. The complex biohybrid structures consist of single components (avidin, differently valent GD-B) and nanostructures. These nanostructures were systematically studied depending on the degree of biotinylation and ligand-receptor stoichiometry by AF4 in combination with dynamic and static light scattering detection. This enables the quantification of composition and calculation of molar masses and radii, which were used to analyze scaling properties and apparent density of the formed structures. These data are compared to hydrodynamic radii obtained by applying the retention theory to the AF4 data. It is shown that depending on their architecture the molecular shape of biohybrid structures is changed from rod-like to spherical toward network-like behavior.
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| 4. |
- Brett, Calvin, et al.
(författare)
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Water-Induced Structural Rearrangements on the Nanoscale in Ultrathin Nanocellulose Films
- 2019
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 52:12, s. 4721-4728
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Tidskriftsartikel (refereegranskat)abstract
- Many nanoscale biopolymer building blocks with defect-free molecular structure and exceptional mechanical properties have the potential to surpass the performance of existing fossil-based materials with respect to barrier properties, load-bearing substrates for advanced functionalities, as well as light-weight construction. Comprehension and control of performance variations of macroscopic biopolymer materials caused by humidity-driven structural changes at the nanoscale are imperative and challenging. A long-lasting challenge is the interaction with water molecules causing reversible changes in the intrinsic molecular structures that adversely affects the macroscale performance. Using in situ advanced X-ray and neutron scattering techniques, we reveal the structural rearrangements at the nanoscale in ultrathin nanocellulose films with humidity variations. These reversible rearrangements are then correlated with wettability that can be tuned. The results and methodology have general implications not only on the performance of cellulose-based materials but also for hierarchical materials fabricated with other organic and inorganic moisture-sensitive building blocks.
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| 5. |
- Brouzet, Christophe, et al.
(författare)
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Characterizing the Orientational and Network Dynamics of Polydisperse Nanofibers on the Nanoscale
- 2019
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 52:6, s. 2286-2295
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Tidskriftsartikel (refereegranskat)abstract
- Polydisperse fiber networks are the basis of many natural and manufactured structures, ranging from high-performance biobased materials to components of living cells and tissues. The formation and behavior of such networks are given by fiber properties such as length and stiffness as well as the number density and fiber-fiber interactions. Studies of fiber network behavior, such as connectivity or rigidity thresholds, typically assume monodisperse fiber lengths and isotropic fiber orientation distributions, specifically for nano scale fibers, where the methods providing time-resolved measurements are limited. Using birefringence measurements in a microfluidic flow-focusing channel combined with a flow stop procedure, we here propose a methodology allowing investigations of length-dependent rotational dynamics of nanoscale polydisperse fiber suspensions, including the effects of initial nonisotropic orientation distributions. Transition from rotational mobility to rigidity at entanglement thresholds is specifically addressed for a number of nanocellulose suspensions, which are used as model nanofiber systems. The results show that the proposed method allows the characterization of the subtle interplay between Brownian diffusion and nanoparticle alignment on network dynamics.
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| 6. |
- Caggiano, N.J., et al.
(författare)
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Local Chain Alignment via Nematic Ordering Reduces Chain Entanglement in Conjugated Polymers
- 2018
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 1520-5835 .- 0024-9297. ; 51:24, s. 10271-10284
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Tidskriftsartikel (refereegranskat)abstract
- Chain entanglements govern the dynamics of polymers and will therefore affect the processability and kinetics of ordering; it follows that through these parameters chain dynamics can also affect charge transport in conjugated polymers. The effect of nematic coupling on chain entanglements is probed by linear viscoelastic measurements on poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) and poly((9,9-dioctylfluorene-2,7-diyl)-alt-(4,7-di(thiophene-2-yl)-2,1,3-benzothiadiazole)-5′,5″-diyl) (PFTBT) with varying molecular weights. We first verify the existence of nematic phases in both PFTBT and PCDTBT and identify nematic-isotropic transition temperatures, TIN, between 260 and 300 °C through a combination of differential scanning calorimetry, polarized optical microscopy, temperature-dependent X-ray scattering, and rheology. In addition, both PCDTBT and PFTBT show a glass transition temperature (Tg) and TIN, whereas only PFTBT has a melting temperature Tm of 260 °C. Comparing the molecular weight dependence of TIN with theoretical predictions of nematic phases in conjugated polymers yields the nematic coupling constant, α = (550 ± 80 K)/T + (2.1 ± 0.1), and the long-chain limit TIN as 350 ± 10 °C for PFTBT. The entanglement molecular weight (Me) in the isotropic phase is extracted to be 11 ± 1 kg/mol for PFTBT and 22 ± 2 kg/mol for PCDTBT by modeling the linear viscoelastic response. Entanglements are significantly reduced through the isotropic-to-nematic transition, leading to a 10-fold increase in Me for PFTBT and a 15-fold increase for PCDTBT in the nematic phase.
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| 7. |
- Chen, Pan, et al.
(författare)
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Quantifying Localized Macromolecular Dynamics within Hydrated Cellulose Fibril Aggregates
- 2019
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Ingår i: Macromolecules. - : AMER CHEMICAL SOC. - 0024-9297 .- 1520-5835. ; 52:19, s. 7278-7288
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Tidskriftsartikel (refereegranskat)abstract
- Molecular dynamics (MD) simulations of C-13 NMR longitudinal relaxation (T-1) distributions were recently established as a powerful tool for characterizing moisture adsorption in natural amorphous polymers. Here, such computational-experimental synergy is demonstrated in a system with intrinsically high structural heterogeneity, namely crystalline cellulose nanofibrils (CNFs) in highly hydrated aggregated state. In such a system, structure-function properties on the nanoscale remain largely uncovered by experimental means alone. In this work, broadly polydispersed experimental C-13 NMR T-1 distributions could be successfully reproduced in simulations and, for the first time, were decomposed into contributions from distinct molecular sources within the aggregated CNFs, namely, (i) the core and (ii) the less-accessible and accessible surface regions of the CNFs. Furthermore, within the surface groups structurally different sites such as (iii) residues with different hydroxymethyl orientations and (iv) center and origin chains could be discerned based on their distinct molecular dynamics. The MD simulations unravel a direct correlation between dynamical and structural heterogeneity at an atomistic-level resolution that cannot be accessed by NMR experiments. The proposed approach holds the potential to enable quantitative interpretation of NMR data from a range of multicomponent high-performance nanocomposites with significantly heterogeneous macromolecular structure.
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| 8. |
- Dang, Hai-Son, et al.
(författare)
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Exploring different cationic alkyl side chain designs for enhanced alkaline stability and hydroxide ion conductivity of anion-exchange membranes
- 2015
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 48:16, s. 5742-5751
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Tidskriftsartikel (refereegranskat)abstract
- In order to systematically improve the performance of anion-exchange membranes (AEMs) for alkaline fuel cells, a series of poly(phenylene oxide)s (PPOs) was tethered with cationic alkyl side chains of different lengths and configurations. PPO was first functionalized with bromomethyl and longer bromoalkyl side chains, respectively, before introducing quaternary ammonium (QA) groups via Menshutkin reactions involving trimethylamine and dimethyloctylamine, respectively. This resulted in samples with QA groups attached to PPO either directly in benzylic positions, or via flexible pentyl and heptyl spacer units, respectively. In addition, the polymers were configured with or without octyl extender chains pendant to the QA groups. All the cationic PPOs had an excellent solubility in, e.g., methanol and dimethyl sulfoxide, and flexible and mechanically robust AEMs with an ion exchange capacity of ∼1.4 mequiv g–1 were cast from solution. Analysis by small-angle X-ray scattering showed that the flexible spacer units greatly facilitated efficient ionic phase separation, regardless of the presence of the extender chain. These AEMs reach very high OH– conductivities, exceeding 0.1 S cm–1 at 80 °C. A clear optimum conductivity was observed for the AEMs with pentyl spacers. Despite a markedly lower water uptake, AEMs configured with additional extender chains still reached a high conductivity, 0.07 S cm–1 at 80 °C. Importantly, the spacer units induced a high alkaline stability and no degradation of these AEMs was detected after storage in 1 M NaOH at 80 °C during 8 days. In comparison, the benchmark materials with QA groups placed in conventional benzylic positions severely degraded under the same conditions. The findings demonstrated that AEMs suitable for fuel cell applications can be achieved by tuning the configuration of flexible cationic alkyl side chains to reach an excellent combination of ionic phase separation, chemical stability, water uptake, and OH– conductivity.
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| 9. |
- Duarte, Mariana, et al.
(författare)
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Uniform Pores in Cross-Linked Polymers by Dispersed Fumed Silica Templating
- 2015
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 48:13, s. 4382-4387
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Tidskriftsartikel (refereegranskat)abstract
- Hydrophobic fumed silica dispersions in organic monomers were explored as a pore-forming system in polymer synthesis. The method developed provides a simple and effective way of controlling the pore size in highly cross-linked polymers. Fumed silica suspensions in divinylbenzene were polymerized with subsequent etching of the silica particles, therefore creating the porosity in the polymer. The resulting polymers are mesoporous materials, exhibiting an extremely narrow pore size distribution with an average pore size of about 100 angstrom, replicating the size of the nanofiller. BET surface areas were found appreciably high (similar to 350 m(2)/g). Furthermore, the rheological behavior of the prepolymerization mixtures was studied to elucidate the formation of the porous network and showed that a tridimensional network of particles is formed at a minimum silica fraction (Phi(v)) of 0.08.
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| 10. |
- Erothu, Harikrishna, et al.
(författare)
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Synthesis, Thermal Processing, and Thin Film Morphology of Poly(3-hexylthiophene)-Poly(styrenesulfonate) Block Copolymers
- 2015
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 48:7, s. 2107-2117
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Tidskriftsartikel (refereegranskat)abstract
- A series of novel block copolymers, processable from single organic solvents and subsequently rendered amphiphilic by thermolysis, have been synthesized using Grignard metathesis (GRIM) and reversible addition-fragmentation chain transfer (RAFT) polymerizations and azide-alkyne click chemistry. This chemistry is simple and allows the fabrication of well-defined block copolymers with controllable block lengths. The block copolymers, designed for use as interfacial adhesive layers in organic photovoltaics to enhance contact between the photoactive and hole transport layers, comprise printable poly(3-hexylthiophene)-block-poly(neopentyl p-styrenesulfonate), P3HT-b-PNSS. Subsequently, they are converted to P3HT-b-poly(p-styrenesulfonate), P3HT-b-PSS, following deposition and thermal treatment at 150 degrees C. Grazing incidence small- and wide-angle X-ray scattering (GISAXS/GIWAXS) revealed that thin films of the amphiphilic block copolymers comprise lamellar nanodomains of P3HT crystallites that can be pushed further apart by increasing the PSS block lengths. The approach of using a thermally modifiable block allows deposition of this copolymer from a single organic solvent and subsequent conversion to an amphiphilic layer by nonchemical means, particularly attractive to large scale roll-to-roll industrial printing processes.
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| 11. |
- Ferreira, Guilherme A., et al.
(författare)
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Hydration-Dependent Hierarchical Structures in Block Copolymer-Surfactant Complex Salts
- 2018
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 51:23, s. 9915-9924
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Tidskriftsartikel (refereegranskat)abstract
- Block copolymer-surfactant "complex salts" (BCPCS), containing one neutral water-soluble block and one polyion/surfactant-ion block, were prepared from poly(acrylamide)-block-poly(acrylic acid) block copolymers by neutralizing the acrylate charges with cationic dodecyl- or hexadecyltrimethylammonium surfactant counterions. The BCPCS were studied in hydrated samples containing 20-99 wt % water (and no additional ions) employing small-angle X-ray scattering (SAXS), dynamic light scattering (DLS), and visual inspection. Selected samples in D2O were also investigated. The results reveal for the first time, for hydrated samples, the formation of ordered hierarchical structures on both block copolymer and surfactant length scales, analogous to structures that have previously been reported for solvent-free block copolymer-surfactant complexes in the solid or melt. The BCPCS structures do not dissolve but display a finite swelling also in the presence of excess water. The structure on the BCP length scale (lamellar or hexagonal) depends only on the BCP, whereas the structure on the CS length scale (hexagonal or micellar cubic) depends on both the surfactant ion and the water content. The results strongly suggest that the observed concentrated hierarchical structures are the equilibrium states for BCPCS in water, although small aggregates formed reproducibly in the dilute regime have been reported for BCPCS and similar systems, collectively known as complex coacervate core micelles (C3Ms).
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| 12. |
- Fuoco, Tiziana, et al.
(författare)
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Redox-Responsive Disulfide Cross-Linked PLA-PEG Nanoparticles
- 2017
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Ingår i: Macromolecules. - : AMER CHEMICAL SOC. - 0024-9297 .- 1520-5835. ; 50:18, s. 7052-7061
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Tidskriftsartikel (refereegranskat)abstract
- We have developed a strategy for the preparation of redox-responsive PEG PLA-based nanoparticles containing disulfide bonds that can be disassembled in the presence of cellular concentrations of glutathione. Functionalized poly-(lactide)s were prepared by ring-opening copolymerization of L-lactide and 3-methyl-6-(tritylthiomethyl)-1,4-dioxane-2,5-dione, a monomer bearing a pendant trityl-thiol group, followed by the postpolymerization modification of trityl-thiol into pyridyl disulfide groups. Polymeric networks composed of PLA and PEG blocks linked by disulfide bonds were prepared by a disulfide exchange reaction between the functionalized PLAs and telechelic PEG having thiol groups at both ends, HS-PEG-SH, in DMF. When dialyzed against water, they assembled into dispersible nanoparticles, with a flowerlike structure having a hydrophobic core and a hydrophilic shell, with sizes in the range 167-300 nm that are suitable for drug delivery. The effects of the number of functional groups, molecular weight, and concentration on the nanoparticle size were evaluated. The stability of the nanoparticles after dilution and the redox-responsive behavior in the presence of different concentrations of glutathione were assessed. The hydrophobic molecule Nile red could be encapsulated in the nanoparticles and then released in the presence of glutathione at cellular concentration.
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| 13. |
- Geng, Lihong, et al.
(författare)
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Understanding the Mechanistic Behavior of Highly Charged Cellulose Nanofibers in Aqueous Systems
- 2018
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 51:4, s. 1498-1506
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Tidskriftsartikel (refereegranskat)abstract
- Mechanistic behavior and flow properties of cellulose nanofibers (CNFs) in aqueous systems can be described by the crowding factor and the concept of contact points, which are functions of the aspect ratio and concentration of CNF in the suspension. In this study, CNFs with a range of aspect ratio and surface charge density (380-1360 mu mol/g) were used to demonstrate this methodology. It was shown that the critical networking point of the CNF suspension, determined by rheological measurements, was consistent with the gel crowding factor, which was 16. Correlated to the crowding factor, both viscosity and modulus of the systems were found to decrease by increasing the charge density of CNF, which also affected the flocculation behavior. Interestingly, an anomalous rheological behavior was observed near the overlap concentration (0.05 wt %) of CNF, at which the crowding factor was below the gel crowding factor, and the storage modulus (G') decreased dramatically at a given frequency threshold. This behavior is discussed in relation to the breakup of the entangled flocs and network in the suspension. The analysis of the mechanistic behavior of CNF aqueous suspensions by the crowding factor provides useful insight for fabricating high-performance nanocellulose-based materials.
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| 14. |
- Gnan, Nicoletta, et al.
(författare)
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In Silico Synthesis of Microgel Particles
- 2017
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 50:21, s. 8777-8786
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Tidskriftsartikel (refereegranskat)abstract
- Microgels are colloidal-scale particles individually made of cross-linked polymer networks that can swell and deswell in response to external stimuli, such as changes to temperature or pH. Despite a large amount of experimental activities on microgels, a proper theoretical description based on individual particle properties is still missing due to the complexity of the particles. To go one step further, here we propose a novel methodology to assemble realistic microgel particles in silico. We exploit the self-assembly of a binary mixture composed of tetravalent (cross-linkers) and bivalent (monomer beads) patchy particles under spherical confinement in order to produce fully bonded networks. The resulting structure is then used to generate the initial microgel configuration, which is subsequently simulated with a bead-spring model complemented by a temperature-induced hydrophobic attraction. To validate our assembly protocol, we focus on a small microgel test case and show that we can reproduce the experimental swelling curve by appropriately tuning the confining sphere radius, something that would not be possible with less sophisticated assembly methodologies, e.g., in the case of networks generated from an underlying crystal structure. We further investigate the structure (in reciprocal and real space) and the swelling curves of microgels as a function of temperature, finding that our results are well described by the widely used fuzzy sphere model. This is a first step toward a realistic modeling of microgel particles, which will pave the way for a careful assessment of their elastic properties and effective interactions.
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| 15. |
- Harris, Kathryn L, et al.
(författare)
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PTFE Tribology and the Role of Mechanochemistry in the Development of Protective Surface Films
- 2015
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Ingår i: Macromolecules. - : American Chemical Society. - 0024-9297 .- 1520-5835. ; 48:11, s. 3739-3745
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Tidskriftsartikel (refereegranskat)abstract
- The wear and friction behavior of ultralow wear polytetrafluoroethylene (PTFE)/α-alumina composites first described by Burris and Sawyer in 2006 has been heavily studied, but the mechanisms responsible for the 4 orders of magnitude improvement in wear over unfilled PTFE are still not fully understood. It has been shown that the formation of a polymeric transfer film is crucial to achieving ultralow wear on a metal countersurface. However, the detailed chemical mechanism of transfer film formation and its role in the exceptional wear performance has yet to be described. There has been much debate about the role of chemical interactions between the PTFE, the filler, and the metal countersurface, and some researchers have even concluded that chemical changes are not an important part of the ultralow wear mechanism in these materials. Here, a "stripe" test allowed detailed spectroscopic studies of PTFE/α-alumina transfer films in various stages of development, which led to a proposed mechanism which accounts for the creation of chemically distinct films formed on both surfaces of the wear couple. PTFE chains are broken during sliding and undergo a series of reactions to produce carboxylate chain ends, which have been shown to chelate to both the metal surface and to the surface of the alumina filler particles. These tribochemical reactions form a robust polymer-on-polymer system that protects the steel countersurface and is able to withstand hundreds of thousands of cycles of sliding with almost no wear of the polymer composite after the initial run-in period. The mechanical scission of carbon-carbon bonds in the backbone of PTFE under conditions of sliding contact is supported mathematically using the Hamaker model for van der Waals interactions between polymer fibrils and the countersurface. The necessity for ambient moisture and oxygen is explained, and model experiments using small molecules confirm the reactions in the proposed mechanism. .
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| 16. |
- Hedlund, Artur, et al.
(författare)
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Diffusion in Ionic Liquid-Cellulose Solutions during Coagulation in Water : Mass Transport and Coagulation Rate Measurements
- 2017
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 50:21, s. 8707-8719
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Tidskriftsartikel (refereegranskat)abstract
- This article describes central features of the mass transport during the coagulation in water of cellulose-1-ethyl-3-methylimidazoium acetate ([C2mim][OAc]) solutions, namely, that the diffusivities are mainly affected by the relative concentrations of water and [C2mim][OAc], that the concentration of cellulose does not affect diffusivities and coagulation rates, that the diffusivities of low-Mw compounds are similar to those in aqueous [C2mim][OAc] solutions without macromolecules, that the polymer concentration is diluted by the large influx of coagulant causing a positive net mass gain, NMG, from diffusive fluxes, and that such NMG, although observed only as a function in time, is also a function in space that has local peaks significantly higher than the mean NMG value. The conclusion from the first three findings was that the diffusion advances through a liquid phase which possesses a continuous pore network and most of the volume. The precipitated cellulose is concentrated into fibrils whose inhibitive effect on the diffusion of small molecules through the surrounding phase is marginal. This key understanding about mass transport during coagulation also simplifies numerical modeling significantly.
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| 17. |
- Hua, Geng, et al.
(författare)
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Phosphazene-Catalyzed Regioselective Ring-Opening Polymerization of rac-1-Methyl Trimethylene Carbonate : Colder and Less is Better
- 2019
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Ingår i: Macromolecules. - : AMER CHEMICAL SOC. - 0024-9297 .- 1520-5835. ; 52:7, s. 2681-2690
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Tidskriftsartikel (refereegranskat)abstract
- The regioselective organocatalytic ring-opening polymerization (ROP) of a 6-membered cyclic carbonate, rac-1-methyl trimethylene carbonate, was studied using phosphazene base (t-BuP2) as the principle catalyst. The influence on the reaction kinetics caused by the reaction temperature (-74-60 degrees C), catalyst loading (0.5-2.5%), and reaction solvent (toluene and tetrahydrofuran) was systematically tuned and followed by H-1 NMR. All studied reactions reached close to or above 90% monomer conversion in 3 h, and all exhibited typical equilibrium polymerization behavior that is inherent to 6-membered cyclic carbonates. Good control over the molecular weight and distribution of the polycarbonate product was obtained in most studied conditions, with M-n ranging from similar to 4k to similar to 20k and D < 1.2. The regioregularity (X-reg) of the resulting polycarbonate was thoroughly studied using various NMR techniques, with the highest X-reg obtained being.0.90. The major influence from the reaction conditions on both the ROP kinetics and X-reg are as follows: higher reaction temperature resulted in a decrease of both; higher catalyst loading resulted in a faster ROP reaction but a slight decrease in X-reg; and toluene being a better solvent resulted in both faster reaction and higher X-reg. Throughout this study, we have demonstrated the possibility to synthesize regioregular aliphatic polycarbonate using an organic base as the ROP catalyst, contrary to the existing studies on similar systems where only metal-base catalysts were in focus and our systems showed similar high X-reg of the product.
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| 18. |
- Hynynen, Jonna, 1987, et al.
(författare)
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Enhanced Electrical Conductivity of Molecularly p-Doped Poly(3-hexylthiophene) through Understanding the Correlation with Solid-State Order
- 2017
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Ingår i: Macromolecules. - : AMER CHEMICAL SOC. - 0024-9297 .- 1520-5835. ; 50:20, s. 8140-8148
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Tidskriftsartikel (refereegranskat)abstract
- Molecular p-doping of the conjugated polymer poly(3-hexylthiophene) (P3HT) with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F4TCNQ) is a widely studied model system. Underlying structure property relationships are poorly understood because processing and doping are often carried out simultaneously. Here, we exploit doping from the vapor phase, which allows us to disentangle the influence of processing and doping. Through this approach, we are able to establish how the electrical conductivity varies with regard to a series of predefined structural parameters. We demonstrate that improving the degree of solid-state order, which we control through the choice of processing solvent and regioregularity, strongly increases the electrical conductivity. As a result, we achieve a value of up to 12.7 S cm(-2) for P3HT:F4TCNQ, We determine the F4TCNQ anion concentration and find that the number of (bound + mobile) charge carriers of about 10(-4) mol cm(-3) is not influenced by the degree of solid-state order. Thus, the observed increase in electrical conductivity by almost 2 orders of magnitude can be attributed to an increase in charge-carrier mobility to more than 10(-1) cm(2) V-1 s(-1). Surprisingly, in contrast to charge transport in undoped P3HT, we find that the molecular weight of the polymer does not strongly influence the electrical conductivity, which highlights the need for studies that elucidate structure property relationships of strongly doped conjugated polymers.
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| 19. |
- Kamerlin, Natasha, et al.
(författare)
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Collapse Dynamics of Core-Shell Nanogels
- 2016
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 49:15, s. 5740-5749
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Tidskriftsartikel (refereegranskat)abstract
- Stimuli-responsive core shell nanogels display collapse properties which are determined by both the core and the shell. We examine the equilibrium properties and the detailed structural changes during a collapse transition of polymer core shell nanoparticles using Brownian dynamics simulations. Gel particles with randomly distributed cross-linking nodes are created. The influence of the cross-linking degree, core/shell mass ratio, and the strength of the interparticle attractive interaction on the collapse behavior is investigated. Both collapsed core and collapsed shell structures are considered and compared with collapsed homopolymer networks. The transition time was found to be reduced with increasing cross-linking degree and inversely related to the depth of the Lennard-Jones potential. Similar to the kinetics of single chain collapse, there is an initial formation of clusters, in this case near cross-linking nodes, and a subsequent coarsening to form a compact globule. Where the nanogels were collapsed into a compact core, the deformation was found to be essentially symmetric, with a significantly slower relaxation time for the shell units compared to the core collapse transition time. Reducing the core size, the shell units were less affected by the presence of a collapsing core. For the system with a collapsing shell, our simulations reveal in some cases an inversion, with the shell compressing and eventually squeezing out the core units. This effect was more pronounced with decreasing cross-linking degree and core/shell mass ratio.
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| 20. |
- Kamerlin, Natasha, et al.
(författare)
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Deformation Behavior and Failure of Bimodal Networks
- 2017
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 50:19, s. 7628-7635
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Tidskriftsartikel (refereegranskat)abstract
- Using computer simulations, we have investigated the deformation and stress-strain behavior of a series of ideal gels without any defects, with a bimodal molecular weight distribution, subject to tensile strains. These networks were prepared with a spatially homogeneous distribution of short and long chains, where all chains are elastically active, without needing to consider possible effects of chain aggregation or entanglements on the physical properties. For all fractions of short chains, the first chains to rupture were the short chains that were initially oriented along the strain axis. The average orientation of the short chains slightly increased with decreasing fraction of short chains. This could be explained by the detailed structure of the network at different compositions. Analysis of the stress-strain relation for the short and long chains showed that the stress was not uniformly shared. Instead, the short chains are more strongly deformed whereas the long chains only make a negligible contribution at smaller strains. The mechanical properties of the bimodal networks at lower fractions of short chains also deviated from the behavior of equivalent unimodal networks with the corresponding average chain length, showing that bimodality alone is sufficient to increase both the maximum extensibility and toughness.
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| 21. |
- Kamerlin, Natasha, et al.
(författare)
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Deformation Behavior of Homogeneous and Heterogeneous Bimodal Networks
- 2017
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 50:23, s. 9353-9359
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, the effect of spatial heterogeneities on the deformation behavior during uniaxial elongation as well as the ultimate properties of bimodal gels consisting of both short and long chains was investigated by molecular simulations. Defect-free networks were created containing dense short-chain clusters and compared with gels having a homogeneous distribution of chains. In both cases, the first chains to rupture were the ones already aligned along the strain axis prior to imposing a strain. The presence of clusters was generally not found to improve the ultimate stress or toughness; the short chains within the clusters were effectively shielded from deformation, even at large fractions of short chains. The heterogeneous network tended to be weaker than the corresponding homogeneous network at a given fraction of short chains, fracturing before any significant deformation of clusters had taken place. The deformation behavior was, however, found to be sensitive to the degree of heterogeneity and the number of intercluster connections. At large fractions of short chains, clustering offered an improvement in the ultimate strain compared to a homogeneous bimodal network and also an equivalent unimodal network with the corresponding number-average chain length, thus providing a small improvement in toughness.
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| 22. |
- Klonos, Panagiotis, et al.
(författare)
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Effects of Molecular Weight below the Entanglement Threshold on Interfacial Nanoparticles/Polymer Dynamics
- 2016
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 49:24, s. 9457-9473
-
Tidskriftsartikel (refereegranskat)abstract
- This work deals with effects of polymer molecular W-m, below the entanglement threshold W-m,W-e, on molecular dynamics of polydimethylsiloxane (PDMS) adsorbed onto silica particles, employing differential scanning calorimetry (DSC) and two dielectric techniques: broadband depolarization currents (TSDC). The rigid amorphous dielectric spectroscopy (BDS) and thermally stimulated polymer fraction at interfaces, RAF(int), was found suppressed for larger W-m by all techniques in qualitative agreement with each other. Results on RAF(int) were supported by evaluating, for the first time, the coverage of hydroxyls at the surfaces of nanoparticles by polymer chains (S relaxation). The mobility of interfacial polymer (alpha(int) relaxation) was followed by BDS and TSDC, showing suppression of dynamics and cooperativity with decreasing W-m. We suggest that interfacial polymer fraction and dynamics are dominated by the concentration of polymer-particle contact points, the latter increasing for smaller W-m due to more free chain ends, as expected below W-m,W-e. Furthermore, adopting models that describe multiple conformations for polymers adsorbed on solid surfaces, we explain our results in terms of promotion of tail/loop-like conformations in the particle-polymer interfacial layer for shorter/longer polymer chains, respectively. The model was further checked by employing surface modification of initial silica, which resulted in smoothening of nanoparticle surface and led to further suppression of RAF(int) and interfacial polymer dynamics.
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| 23. |
- Koo, Jun Mo, et al.
(författare)
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Nonstop Monomer-to-Aramid Nanofiber Synthesis with Remarkable Reinforcement Ability
- 2019
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 52:3, s. 923-934
-
Tidskriftsartikel (refereegranskat)abstract
- Aramid nanofibers (ANFs), typically produced by exfoliating aramid microfibers (Kevlar) in alkaline media, exhibit excellent mechanical properties and have therefore attracted increased attention as nanoscale building blocks. However, the preparation of aramid microfibers involves laborious and hazardous processes, which limits the industrial-scale use of ANFs. This work describes a facile and direct monomer-to-ANF synthesis via an as-synthesized intermediate low-molecular-weight poly(p-phenylene terephthalamide) (PPTA) without requiring the environmentally destructive acids and high-order shearing processes. Under the employed conditions, PPTA immediately dissociates and self-assembles into ANFs within a time period of 15 h, which is much shorter than the time of 180 h (not including the Kevlar preparation time) required for the Kevlar-to-ANF conversion. Interestingly, the fabricated ANFs exhibit nanoscale dimensions and thermoplastic polyurethane (TPU) reinforcing effects similar to those of Kevlar-derived ANFs; i.e., a 1.5-fold TPU toughness improvement and a maximum ultimate tensile strength of 84 MPa are achieved at an ANF content of only 0.04 wt %. Remarkable reinforcement ability investigated by comprehensive analytical data comes from ANFs, which disturb ordered hydrogen bonding in hard segments and induce strain hardening along the elongation pathway. Thus, the developed approach paves the way to industrial-scale production of ANFs and related nanocomposites.
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| 24. |
- Korolkovas, Airidas, et al.
(författare)
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Polymer Brush Collapse under Shear Flow
- 2017
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 50:3, s. 1215-1224
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Tidskriftsartikel (refereegranskat)abstract
- Shear responsive surfaces offer potential advances in a number of applications. Surface functionalization using polymer brushes is one route to such properties, particularly in the case of entangled polymers. We report on neutron reflectometry measurements of polymer brushes in entangled polymer solutions performed under controlled shear as well as coarse-grained computer simulations corresponding to these interfaces. Here we show a reversible and reproducible collapse of the brushes, increasing with the shear rate. Using two brushes of greatly different chain lengths and grafting densities, we demonstrate that the dynamics responsible for the structural change of the brush are governed by the free chains in solution rather than the brush itself, within the range of parameters examined. The phenomenon of the brush collapse could find applications in the tailoring of nanosensors and as a way to dynamically control surface friction and adhesion.
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| 25. |
- Kozhuharov, Svilen, et al.
(författare)
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Persistence Length of Poly(vinyl amine) : Quantitative Image Analysis versus Single Molecule Force Response
- 2018
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Ingår i: Macromolecules. - : AMER CHEMICAL SOC. - 0024-9297 .- 1520-5835. ; 51:10, s. 3632-3639
-
Tidskriftsartikel (refereegranskat)abstract
- Single molecules of poly(vinyl amine) are analyzed in the adsorbed state by atomic force microscopy (AFM) in two different ways. First, high-resolution images of individual adsorbed polymers were recorded in monovalent electrolyte solutions. The backbone of the imaged polymers was digitized, and the directional correlation function and internal mean-square end-to-end distance were evaluated. These quantities were analyzed with the wormlike chain (WLC) model, and the persistence length was extracted. Second, individual polymer chains were picked up from the surface, and their force extension behavior was recorded in the same electrolyte solutions. These force profiles were also interpreted in terms of the WLC model, whereby the elastic contribution was also considered. Both techniques yield the persistence length of the polymer. From imaging one obtains a persistence length of about 1.6 nm, while the force experiments yield a value around 0.51 nm. We suspect that the force experiments reflect the intrinsic part of the persistence length, while the imaging experiments yield the persistence length including the electrostatic
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| 26. |
- Medina, Lilian, 1992-, et al.
(författare)
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Nanostructure and Properties of Nacre-Inspired Clay/Cellulose Nanocomposites—Synchrotron X-ray Scattering Analysis
- 2019
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 52:8, s. 3131-3140
-
Tidskriftsartikel (refereegranskat)abstract
- Nacre-inspired clay nanocomposites have excellent mechanical properties, combined with optical transmittance, gas barrier properties, and fire retardancy, but the mechanical properties are still below predictions from composite micromechanics. The properties of montmorillonite clay/nanocellulose nanocomposite hybrids are investigated as a function of clay content and show a maximum Young’s modulus as high as 28 GPa. Ultimate strength, however, decreases from 280 to 125 MPa between 0 and 80 wt % clay. Small-angle and wide-angle X-ray scattering data from synchrotron radiation are analyzed to suggest nanostructural and phase interaction factors responsible for these observations. Parameters discussed include effective platelet modulus, platelet out-of-plane orientation distribution, nanoporosity, and platelet agglomeration state.
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| 27. |
- Moyassari, Ali, et al.
(författare)
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Molecular Dynamics Simulations of Short-Chain Branched Bimodal Polyethylene : Topological Characteristics and Mechanical Behavior
- 2019
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 52:3, s. 807-818
-
Tidskriftsartikel (refereegranskat)abstract
- It has previously been shown that polyethylene (PE) with a bimodal molar mass distribution has a high fracture toughness. Our approach has been to use coarse-grained (CG) molecular dynamics (MD) simulations to investigate the effects of including short-chain branches in the high molar mass fraction of bimodal PE on topological features and mechanical behavior of the material. The CG potentials were derived, validated, and utilized to simulate melt equilibration, cooling, crystallization, and mechanical deformation. Crystallinity, tie chain, and entanglement concentrations were continuously monitored. During crystallization, the branched bimodal systems disentangled to a lesser degree and ended up with a higher entanglement density than the linear bimodal systems simulated in our previous study. The increase in entanglement concentration was proportional to the content of the branched high molar mass fraction. A significantly higher tie chain concentration was obtained in the short-chain branched bimodal systems than in the linear systems. The increase in the number of ties was more pronounced than the increase in the number of entanglements. The tie chain concentration was not proportional to the content of the high molar mass fraction. Despite a lower crystal thickness and content, the elastic modulus and yield stress values were higher in the branched bimodal systems. A more pronounced strain hardening region was observed in the branched systems. It was suggested that the higher tie chain and entanglement concentration prior to the deformation, the more extensive disentanglement during the deformation, and the disappearance of formed voids prior to failure point were the reasons for the observed higher toughness of the short-chain branched bimodal PE compared with that of the linear bimodal systems. The toughest system, which contained respectively 25 and 75 wt % low molar mass and branched high molar mass fractions, had the highest tie chain concentration and the second highest entanglement concentration of the simulated systems.
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| 28. |
- Ninarello, Andrea, et al.
(författare)
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Modeling Microgels with a Controlled Structure across the Volume Phase Transition
- 2019
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 52:20, s. 7584-7592
-
Tidskriftsartikel (refereegranskat)abstract
- Thermoresponsive microgels are soft colloids that find widespread use as model systems for soft matter physics. Their complex internal architecture, made of a disordered and heterogeneous polymer network, has been so far a major challenge for computer simulations. In this work, we put forward a coarse-grained model of microgels whose structural properties are in quantitative agreement with results obtained with small-angle X-ray scattering experiments across a wide range of temperatures, encompassing the volume phase transition. These results bridge the gap between experiments and simulations of individual microgel particles, paving the way to theoretically address open questions about their bulk properties with unprecedented nano- and microscale resolution.
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| 29. |
- Olsén, Peter, et al.
(författare)
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Macromolecular Design via an Organocatalytic, Monomer-Specific and Temperature-Dependent "On/Off Switch" : High Precision Synthesis of Polyester/Polycarbonate Multiblock Copolymers
- 2015
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 48:6, s. 1703-1710
-
Tidskriftsartikel (refereegranskat)abstract
- The employment of a monomer-specific on/off switch was used to synthesize a nine-block copolymer with a predetermined molecular weight and narrow distribution (D = 1.26) in only 2.5 h. The monomers consisted of a six-membered cyclic carbonate (i.e., 2-allyloxymethyl-2-ethyl-trimethylene carbonate (AOMEC)) and epsilon-caprolactone (epsilon CL), which were catalyzed by 1,5,7-triazabicyclo[4.4.0]-dec-5-ene (TBD). The dependence of polymerization rate with temperature was different for the two monomers. Under similar reaction conditions, the ratio of the apparent rate constant of AOMEC and epsilon CL [k(p)(app)(AOMEC)/k(p)(app)(epsilon CL)] changes from 400 at T = -40 degrees C to 50 at T = 30 degrees C and 10 at T = 100 degrees C. Therefore, by decreasing the copolymerization temperature from 30 degrees C to -40 degrees C, the conversion of epsilon CL can be switched off, and by increasing the temperature to 30 degrees C, the conversion of epsilon CL can be switched on again. The addition of AOMEC at T = -40 degrees C results in the formation of a pure carbonate block. The cyclic addition of AOMEC to a solution of epsilon CL along with a simultaneous temperature change leads to the formation of multiblock copolymers. This result provides a new straightforward synthetic route to degradable multiblock copolymers, yielding new interesting materials with endless structural possibilities.
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| 30. |
- Olsson, Joel S., et al.
(författare)
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Poly(N,N-diallylazacycloalkane)s for anion-exchange membranes functionalized with N-spirocyclic quaternary ammonium cations
- 2017
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 50:7, s. 2784-2793
-
Tidskriftsartikel (refereegranskat)abstract
- The alkaline stability of organic cations tethered to anion-exchange membranes (AEMs) is essential for the long-term performance of alkaline membrane fuel cells and electrolyzers. Here, we have prepared and studied the thermal and alkaline stability of a series of polyelectrolytes functionalized with N-spirocyclic quaternary ammonium (QA) cations. N,N-diallyl azacycloalkane quaternary salts were readily synthesized by diallylation of pyrrolidine, piperidine, azepane, and morpholine, respectively. These monomers were employed in radical-initiated cyclo-polymerizations to obtain the target poly(N,N-diallyl azacycloalkane)s. 1H NMR spectroscopy revealed that the stability of the polyelectrolytes in 2 M KOD/D2O solutions critically depended on the ring size and the absence of additional heteroatoms in the ring. Thus, poly(N,N-diallyl piperidinium) showed the highest alkaline stability, with only minor signs of degradation at 120 °C after 14 days, while the polyelectrolytes based on the morpholine and azepane rings clearly degraded via both Hofmann elimination and ring-opening substitution already at 90 °C. Crosslinked water non-soluble AEMs were prepared by copolymerizing N,N-diallyl piperidinium chloride with methylbenzyldiallyl ammonium groups tethered to poly(phenylene oxide). These transparent and mechanically robust AEMs reached high OH– conductivities, above 0.1 S cm-1 at 80 °C. The present work demonstrate the high alkaline stability of suitably configured N-spirocyclic QA cations, which will open up new prospects for readily accessible high performance polyelectrolytes and membranes.
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| 31. |
- Patil, Nagaraj, et al.
(författare)
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Surface- and Redox-Active Multifunctional Polyphenol-Derived Poly(ionic liquid)s: Controlled Synthesis and Characterization
- 2016
-
Ingår i: Macromolecules. - : AMER CHEMICAL SOC. - 0024-9297 .- 1520-5835. ; 49:20, s. 7676-7691
-
Tidskriftsartikel (refereegranskat)abstract
- Combining the redox activity and remarkable adhesion propensity of polyphenols (such as catechol or pyrogallol) with the numerous tunable properties of poly(ionic liquid)s (PILs) is an attractive route to design inventive multifunctional macromolecular platforms. In this contribution, we describe the first synthesis of a novel family of structurally well-defined PILs functionalized with catechol/pyrogallol/phenol pendants by organometallic-mediated radical polymerization (OMRP) using an alkyl cobalt(III) complex as initiator and mediating agent. The living character of the chains is also exploited to produce di- and triblock PILs, and the facile counteranion exchange reactions afforded a library of PILs-bearing free phenol/catechol/pyrogallol moieties. Electrochemical investigations of catechol/pyrogallol-derived PILs in aqueous medium demonstrated the characteristic catechol to o-quinone transformations, whereas, quasi reversible doping/undoping with supporting electrolyte cations (Li+/tetrabutylammonium(+)) has been observed in organic media, suggesting a bright future for this new family of redox-active PILs as cathode material for secondary energy storage devices. Also, pendant catechol/pyrogallol groups mediated sustained anchoring onto the gold surface conferred PILs properties to the interface. As a proof-of-concept, both the adsorption and inhibition of proteins on polymer modified surfaces have been demonstrated in real time using the quartz crystal microbalance with dissipation technique. The exquisite physicochemical tunability of these innovative surface- and redox-active PILs makes them excellent candidates for a broad range of potential applications, including "smart surfaces" and electrochemical energy storage devices.
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| 32. |
- Pronoitis, Charalampos, et al.
(författare)
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Biobased Polyamide Thermosets : From a Facile One-Step Synthesis to Strong and Flexible Materials
- 2019
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 52:16, s. 6181-6191
-
Tidskriftsartikel (refereegranskat)abstract
- Biobased polyamide (PA) thermosets composed of renewable ethylene brassylate were synthesized through a one-step reaction under solvent-free conditions, at 100 degrees C in the presence of an organocatalyst. Under these conditions, thermoset formation times as low as 10 min were achieved. The thermosets were easily prepared as thin, transparent films with high strength, flexibility, and high thermal stability. The ester-to-amine content and formation of ethylene glycol in situ as a byproduct of the reaction were studied and correlated with the final properties of the materials. Crystalline oligoester segments were identified as a result of ring-opening polymerization and were shown to have a beneficial effect on the mechanical properties of the thermosets and endowed shape-memory behavior. In contrast to other routes, employing multistep monomer preparation, harsh conditions, and chlorinated reagents, this procedure contributed to the development of sustainable, functional PA thermosets.
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| 33. |
- Schottner, S., et al.
(författare)
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Amine-Containing Block Copolymers for the Bottom-Up Preparation of Functional Porous Membranes
- 2019
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 52:7, s. 2631-2641
-
Tidskriftsartikel (refereegranskat)abstract
- The remarkable ability of biological systems to specifically recognize, sort, and process molecules encourages the development of novel bio-inspired membranes and interfaces. Herein, we focus on the functionalization of amphiphilic polystyrene-block-poly(2-hydroxyethyl methacrylate) (PS-b-PHEMA) with the amino acid glycine yielding polar block segments with primary amine functionalities. Excellent control over the tailored block copolymer (BCP) synthesis and functionalization is proven by size exclusion chromatography (SEC), H-1 solution NMR, and N-15 solid state NMR spectroscopy. For the first time, BCPs containing primary amines were used for the self-assembly and non-solvent induced phase separation (SNIPS) process for the preparation of isoporous and integral asymmetric membranes. Hexagonally arranged open pores with diameters of 19 rim were obtained as shown by scanning electron microscopy (SEM), atomic force microscopy (AFM), and pH-dependent water flux measurements. Additionally, the primary amine was subjected to convenient postmodification protocols. For instance, (fluorescent) dye molecules could be easily incorporated into the membrane structure, and peptide synthesis on the inner pore wall of the membrane could be accomplished. These novel and tailored porous materials will pave the way to a new generation of BCP membranes containing bio-inspired moieties and functionalities at the interfaces.
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| 34. |
- Selegård, Robert, et al.
(författare)
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Distinct Electrostatic Interactions Govern the Chiro-Optical Properties and Architectural Arrangement of Peptide-Oligothiophene Hybrid Materials
- 2017
-
Ingår i: Macromolecules. - : AMER CHEMICAL SOC. - 0024-9297 .- 1520-5835. ; 50:18, s. 7102-7110
-
Tidskriftsartikel (refereegranskat)abstract
- The development of chiral optoelectronic materials is of great interest due to their potential of being utilized in electronic devices, biosensors, and artificial enzymes. Herein, we report the chiral optical properties and architectural arrangement of optoelectronic materials generated from noncovalent self-assembly of a cationic synthetic peptide and five chemically defined anionic pentameric oligothiophenes. The peptide-oligothiophene hybrid materials exhibit a three-dimensional ordered helical structure and optical activity in the pi-pi* transition region that are observed due to a single chain induced chirality of the conjugated thiophene backbone upon interaction with the peptide. The latter property is highly dependent on electrostatic interactions between the peptide and the oligothiophene, verifying that a distinct spacing of the carboxyl groups along the thiophene backbone is a major chemical determinant for having a hybrid material with distinct optoelectronic properties. The necessity of the electrostatic interaction between specific carboxyl functionalities along the thiophene backbone and the lysine residues of the peptide, as well as the induced circular dichroism of the thiophene backbone, was also confirmed by theoretical calculations. We foresee that our findings will aid in designing optoelectronic materials with dynamic architectonical precisions as well as offer the possibility to create the next generation of materials for organic electronics and organic bioelectronics.
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| 35. |
- Sproll, Véronique, et al.
(författare)
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Radiostation Grafted Ion-Conducting Membranes: The Influence of Variations in Base Film Nanostructure
- 2016
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 49:11, s. 4253-4264
-
Tidskriftsartikel (refereegranskat)abstract
- The proton exchange membrane (PEM) is a key element of a polymer electrolyte fuel cell, and radiation-grafting is an attractive option for the synthesis of PEMs. Via a systematic investigation of a well-defined model material, sulfonated polystyrene grafted poly(ethylene-alt-tetrafluoroethylene), ETFE-g-PS(SA), we show that the performance and stability of radiation-grafted PEMs in fuel cells strongly depends on the microstructure of the underlying base polymer. The nanoscale structure of the base polymers, grafted films, and membranes is probed by small-angle scattering, and the nanoscale proton dynamics is probed by quasi-elastic neutron scattering. The results of these techniques correlated with fuel cell relevant properties—including proton conductivity and water uptake—and fuel cell performance clearly indicate that differences in the arrangement of the crystalline phase in the otherwise chemically identical semicrystalline base films can have considerable impact, representing an essential aspect to consider in the development of proton exchange membranes prepared via preirradiation grafting.
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| 36. |
- Stornes, Morten, et al.
(författare)
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Monte Carlo Simulations of Complexation between Weak Polyelectrolytes and a Charged Nanoparticle. Influence of Polyelectrolyte Chain Length and Concentration
- 2017
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 50:15, s. 5978-5988
-
Tidskriftsartikel (refereegranskat)abstract
- Complexation between multiple weak polyacid chains and a positively charged spherical nanoparticle has been studied by means of Monte Carlo simulations. By considering titration curves, it is found that variations in the polyacid chain length and concentration and the polyacid-to-nanoparticle mixing ratio influence the ionization of the system. For larger mixing ratios and longer chain lengths, the titration curves start to exhibit complex shapes with multiple inflection points. We also find that in some cases it is possible to differentiate between free and adsorbed chains, based on the charge probability distribution and the probability distribution of the gyration radius. Furthermore, the adsorption of weak polyacids has been compared with that of strong polyacids, and the fraction of adsorbed monomers is found to be slightly larger for the strong polyacids. In addition, the fraction of adsorbed chains can be much lower for the weak polyacids due to their ability to concentrate charge in few chains.
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| 37. |
- Svenningsson, Leo, 1990, et al.
(författare)
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Molecular Orientation Distribution of Regenerated Cellulose Fibers Investigated with Polarized Raman Spectroscopy
- 2019
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 1520-5835 .- 0024-9297. ; 52:10, s. 3918-3924
-
Tidskriftsartikel (refereegranskat)abstract
- The molecular orientation distribution of polymeric fibers influences physical properties. We present a novel method of analyzing polarized Raman experiments to determine molecular orientation, which is based on exchanging the Legendre polynomial approach with a wrapped Lorentzian function, as determined from a prescreening of X-ray scattering patterns. This method removes the need for performing right angle scattering experiments while avoiding common approximations. The molecular orientation of regenerated cellulose fibers, using the presented method, is shown to correlate well with X-ray scattering and an analogous experiment using solid-state NMR spectroscopy. Challenges of quantitatively measuring molecular anisotropy occur with semi-crystalline, partially modified, or composite materials. As such, a plethora of techniques, each with a unique chemical selectivity, is paramount for material characterization.
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| 38. |
- Tao, Qiang, 1987, et al.
(författare)
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D-A(1)-D-A(2) Copolymers with Extended Donor Segments for Efficient Polymer Solar Cells
- 2015
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 1520-5835 .- 0024-9297. ; 48:4, s. 1009-1016
-
Tidskriftsartikel (refereegranskat)abstract
- Typically a donor-acceptor (D-A) design strategy is used for engineering the bandgap of polymers for solar cells. However, in this work, a series of alternating D-A(1-)D-A(2) copolymers PnTQTI(F) were synthesized and characterized with oligothiophenes (nT, n = 1, 2, 3) as the donor and two electron-deficient moieties, quinoxaline and isoindigo, as the acceptors in the repeating unit. We have studied the influence of the donor segments with different numbers of thiophene units and the effect of the addition of fluorine to the quinoxaline unit of the D-A(1)-D-A(2) polymers. The photophysical, electrochemical, and photovoltaic properties of the polymers were examined via a range of techniques and related to theoretical simulations. On increasing the length of the donor thiophene units, broader absorption spectra were observed in addition to a sequential increase in HOMO levels, while the LUMO levels displayed very small variations. The addition of fluorine to the quinoxaline unit not only decreased the HOMO levels of the resulting polymers but also enhanced the absorption coefficients. A superior photovoltaic performance was observed for the P3TQTI-F-based device with a power conversion efficiency (PCE) of 7.0%, which is the highest efficiency for alternating D-A(1)-D-A(2) polymers reported to date. The structureproperty correlations of the PnTQTI(F) polymers demonstrate that varying of the length of the donor segments is a valuable method for designing high-performance D-A(1)-D-A(2) copolymers and highlight the promising nature of D-A(1)-D-A(2) copolymers for efficient bulk-heterojunction solar cells.
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| 39. |
- Wang, Ruifu, et al.
(författare)
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Morphology and Flow Behavior of Cellulose Nanofibers Dispersed in Glycols
- 2019
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 52:15, s. 5499-5509
-
Tidskriftsartikel (refereegranskat)abstract
- Understanding the morphology and flow behavior of cellulose nanofibers (CNFs) dispersed in organic solvents can improve the process of fabricating new cellulose-based nanocomposites. In this study, jute-based 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO)-oxidized CNFs with two different charge densities (0.64 and 1.03 mmol/g) were dispersed in ethylene glycol (EG) and propylene glycol (PG) using the solvent exchange method. The morphology and dimensions of CNFs in dry and suspension states were characterized using transmission electron microscopy, atomic force microscopy, and small-angle X-ray scattering techniques. The results showed that the cross-sectional dimensions remained the same in different solvents. Rheological measurements revealed that CNF suspensions in water or glycol (EG and PG) behaved similar to typical polymer solutions with a solvent-independent overlap concentration corresponding to the crowding factor of about 14. Furthermore, a thixotropic behavior was found in the concentrated CNF/glycol systems as observed in typical CNF aqueous suspensions. The fact that TEMPO-oxidized CNFs can be well dispersed in organic solvents opens up new possibilities to improve the CNF–polymer matrix blending, where the use of a viscous solvent can delay the transition to turbulence in processing and improve the control of fiber orientation because of a slower Brownian diffusive motion.
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| 40. |
- Wohlfarth, Andreas, et al.
(författare)
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Proton dissociation of sulfonated polysulfones: influence of molecular structure and conformation
- 2015
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 48:4, s. 1134-1143
-
Tidskriftsartikel (refereegranskat)abstract
- The dissociation behavior of proton conducting sulfonated polysulfones has been investigated by combining electrophoretic NMR, pulsed magnetic field gradient NMR and conductivity meas- urements on monomeric and polymeric samples with concentrations of ionic groups in the range where dissociation is not complete (IEC = 4.55 – 7.04 meq g-1). In this regime, counterion con- densation is shown to critically depend on details of the molecular structure, and all atom MD simulations reveal the formation of well-defined ionic aggregates (e.g. triple ions). The corre- sponding global minima of the free energy are suggested to be the result of a delicate balance of the energetics involved in conformational changes, formation of ionic aggregates and solvation. This goes beyond Manning’s counterion condensation theory and has important implications for the development of membranes with high ionic conductivity as needed for many electrochemical applications such as fuel cells and batteries.
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| 41. |
- Wu, L. F., et al.
(författare)
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Ground State Host-Guest Interactions upon Effective Dispersion of Regioregular Poly(3-hexylthiophene) in Poly(9,9-dioctylfluorene-alt-benzothiadiazole)
- 2015
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 1520-5835 .- 0024-9297. ; 48:24, s. 8765-8772
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Tidskriftsartikel (refereegranskat)abstract
- Regioregular poly(3-hexylthiophene), (rr-P3HT), is widely regarded as an archetypical semiconducting electron-donor polymer in bulk heterojunction solar cells, mainly due to its notable exciton and charge transport properties. Conversely, its use in photonic/lighting devices received little interest owing to its low emission quantum yield in the solid state, related to its large tendency to self-organize into lamellar domains with highly nonemissive character. We present experimental evidence pointing to a large miscibility of P3HT in poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT), accompanied by mutual pi-pi interactions. Concomitant to this effect, the emission properties of P3HT:F8BT blends, which are attributed to heterogeneous interchain complexes, experience a significant improvement, with photoluminescence quantum efficiency (PLQE) values approaching 25% (almost a 7-fold efficiency enhancement with respect to neat/aggregated rr-P3HT). Our results open up new prospects for improved photonic properties through appropriate control of interchain interactions.
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| 42. |
- Xie, R., et al.
(författare)
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Glass Transition Temperature of Conjugated Polymers by Oscillatory Shear Rheometry
- 2017
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 1520-5835 .- 0024-9297. ; 50:13, s. 5146-5154
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Tidskriftsartikel (refereegranskat)abstract
- The stiff backbones of conjugated polymers can lead to a rich phase behavior that includes both crystalline and liquid crystalline phases, making measurements of the glass transition challenging. In this work, the glass transitions of regioregular poly(3-hexylthiophene-2,5-diyl) (RR P3HT), regiorandom (RRa) P3HT, and poly((9,9-bis(2-octyl)-fluorene-2,7-diyl)-alt-(4,7-di(thiophene-2-yl)-2,1,3-benzothiadiazole)-5′,5″-diyl) (PFTBT) are probed by linear viscoelastic measurements as a function of molecular weight. We find two glass transition temperatures (T g 's) for both RR and RRa P3HT and one for PFTBT. The higher T g , T α , is associated with the backbone segmental motion and depends on the molecular weight, such that the Flory-Fox model yields T α = 22 and 6 °C in the long chain limit for RR and RRa P3HT, respectively. For RR P3HT, a different molecular weight dependence of T α is seen below M n = 14 kg/mol, suggesting this is the typical molecular weight of intercrystal tie chains. The lower T g (T αPE ≈ -100 °C) is associated with the side chains and is independent of molecular weight. RRa P3HT exhibits a lower T α and higher T αPE than RR P3HT, possibly due to a different degree of nanophase separation between the side chains and the backbones. In contrast, PFTBT only exhibits one T g above -120 °C, at 144 °C in the long chain limit.
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| 43. |
- Xu, Huan, et al.
(författare)
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Thermostable and impermeable "nano-barrier walls" constructed by poly(lactic acid) stereocomplex crystal decorated graphene oxide nanosheets
- 2015
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 48:7, s. 2127-2137
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Tidskriftsartikel (refereegranskat)abstract
- In contrast to the relatively clear understanding of epitaxial crystallization induced by one-dimensional nanofillers, the underlying interfacial interactions between polymer crystals and two-dimensional graphene oxide (GO) nanosheets are something of a mystery. Here, the GO-assisted formation of poly(lactic acid) (PLA) stereocomplex crystals (SCs) is disclosed from the quantitative structural analysis to the direct morphological observations at multiscale and the interaction mechanism at the molecular level. It is unexpected to observe that the edges of GO featuring rich grooves and ultralow thickness were ready to induce a layer of ordered lamellae, in clear contrast to the random growth of lamellae on the basal planes. The origin of GO-induced crystallization was appraised from the interaction point of view as indicated by the evident red-shift of a set of functional groups in the Fourier transform infrared spectroscopy spectra. More importantly, the GO nanosheets, albeit presented at an extremely low content (0.05 wt %), decorated by the preferred formation of SCs enabled the simultaneous enhancement of gas barrier properties and resistance to heat distortion. Specifically, the unique combination of greatly improved heat deformation temperature (HDT) and low oxygen permeability coefficient (PO2) for the composite crystallized at 165 °C was demonstrated (146.5 °C and 0.95 × 10-15 cm3 cm cm-2 s-1 Pa-1), outperforming pure PLA with an increment of 75% and a decrease of 77% in HDT and PO2, respectively. The proposed methodology affords elucidation of well-tailored thermal and barrier properties, which may motivate further extension of this rational design to other material combinations.
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| 44. |
- Yang, Xi, et al.
(författare)
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Two step extrusion process : From thermal recycling of PHB to plasticized PLA by reactive extrusion grafting of PHB degradation products onto PLA chains
- 2015
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 48:8, s. 2509-2518
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Tidskriftsartikel (refereegranskat)abstract
- A green and industrially viable two-step process was demonstrated for toughening polylactide (PLA) without compromising the biobased and biodegradable nature. First, poly(3-hydroxybutyrate) (PHB) biopolymer was thermally degraded in an extruder to create PHB oligomers (dPHB) with functional end-groups suitable for further reactions. Second, a reactive extrusion process was developed to covalently anchor dPHB onto the main chain of PLA. PLA with 20% (w/w) grafted dPHB demonstrated an impressive elongation at break of 538%, 66 times higher than that of pure PLA and significantly higher than the elongation at break of the corresponding physical blend. At the same time WAXD measurements illustrated that grafting significantly increased the crystallization ability of PLA. We present a viable recycling route for PHB and a highly promising approach for fully biobased toughened PLA with covalently anchored PHB plasticizers.
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| 45. |
- Yuan, Yuan, et al.
(författare)
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Multiple Chain Packing and Phase Composition in Regioregular Poly(3-butylthiophene) Films
- 2016
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 1520-5835 .- 0024-9297. ; 49:24, s. 9493-9506
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Tidskriftsartikel (refereegranskat)abstract
- On the basis of different film preparation conditions, we address the phase composition and thiophene main-chain and butyl side-chain organization of three regioregular poly(3-butylthiophene) (P3BT) samples prepared by drop-casting. These samples are readily identified by wide-angle X-ray diffraction (WAXD) with the structural P3BT polymorphs commonly referred to as forms I, I?, and II. Here, we show by means of WAXD, solid-state nuclear magnetic resonance (NMR), and Fourier-transform infrared spectroscopy (FTIR) that the P3BT samples identified with these polymeric forms (I, I?, and II) do not contain a single, unique crystalline phase and an amorphous phase, but additionally consist of one (form II) or two (forms I and I?) distinct crystalline phases. Each of the crystalline phases is associated with specific thiophene main-chain packing arrangements and butyl side-chain organizations. We provide a spectroscopic identification for each of the P3BT crystalline phases, enabling a detailed and consistent picture of molecular order and polymer main-chain and side-chain packing. Thus, our results are expected to be valuable in future studies of poly(3-alkylthiophene) (P3AT) thin films, where in particular FTIR studies will permit quick and easy access to both phase composition and identification of multiple thiophene main-chain packing structures.
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| 46. |
- Zhu, Liangliang, et al.
(författare)
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Unimolecular Photopolymerization of High-Emissive Materials on Cylindrical Self-Assemblies
- 2015
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 48:15, s. 5099-5105
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Tidskriftsartikel (refereegranskat)abstract
- We report a novel self-assembly pathway from a bis(imidazolyl) diphenyl-diacetylene (DPDA) compound as a realization of self-templated photopolymerization with high polymerization degrees. The work takes advantage of a cylindrical self-assembly that strengthens the preorganization of the diphenyl-diacetylene moiety at the single molecular level. On this basis, photopolymerization of DPDA can be conducted smoothly to form high-molecular-weight polydiphenyl diacetylene. Such a cylindrical self-assembly is highly dependent on molecular structure, and control studies show that only oligomers can be formed on random self-assemblies from a monoimidazolyl or nonimidazolyl diphenyl-diacetylene compound. Moreover, the cylindrical self-assembly based systems bear aggregation-induced emission enhancement characteristics and are solution processable. The leading thin-film could afford a selectively tunable function in luminescent micropatterns.
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