| 1. |
- Aziz, Shazed, et al.
(författare)
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Effect of anisotropic thermal expansion on the torsional actuation of twist oriented polymer fibres
- 2017
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Ingår i: Polymer. - : Elsevier. - 0032-3861 .- 1873-2291. ; 129, s. 127-134
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Tidskriftsartikel (refereegranskat)abstract
- Torsional actuation of twisted polymer fibres is the basis for high performance tensile actuation when these fibres are formed into coils. The thermally-induced torsional actuation of twisted polyamide-6 fibres can be predicted by a single helix approximation when the measured diameter and length direction thermal expansion coefficients are known. The single helix model illustrates the sensitivity of the magnitude of torsional actuation to the volume expansion anisotropy for a given volume change. The applicability of the model has been further assessed by investigating three polymer fibres that display different thermal expansion anisotropies. Commercially available polyethylene, polypropylene and polyamide-6 fibres were twisted to the maximum extent without coiling and then heat treated to fix the twisted structure. Heating the twisted fibres between 26 and 62 °C resulted in a partial untwist which was reversed during cooling. The single-helix model of the twisted fibres was used to accurately predict the torsional stroke based on the measured fibre length and diameter change during heating. Comparative torsional stroke of twisted polyamide-6, polyethylene and polypropylene was explained in terms of materials thermo-physical properties. Generated blocked torques was also correctly predicted by the single-helix model when combined with the measured fibre torsional stiffness. Variances between torsional stiffnesses were found to be dependent of different anisotropic thermal properties of tested fibres.
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| 2. |
- Bergfelt, Andreas, et al.
(författare)
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d8-poly(methyl methacrylate)-poly[(oligo ethylene glycol) methyl ether methacrylate] tri-block-copolymer electrolytes : Morphology, conductivity and battery performance
- 2017
-
Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 131, s. 234-242
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Tidskriftsartikel (refereegranskat)abstract
- A series of deuterated tri-block copolymers with the general structure d(8)-PMMA-POEGMA-d(8)-PMMA, with variation in d(8)-PMMA chain length, were synthesized using sequential controlled radical polymerization (ATRP). Solid polymer electrolytes (SPEs) were produced by blending tri-block copolymers and lithium bis(trifluoro methylsulfonate) (LiTFSI). Small-angle neutron scattering (SANS) was used to study the bulk morphology of the deuterated tri-block copolymer electrolyte series at 25 degrees C, 60 degrees C and 95 degrees C. The lack of a second T-g in DSC analysis together with modelling with the random phase approximation model (RPA) confirmed that the electrolytes are in the mixed state, with negative Flory-Huggins interaction parameters. AC impedance spectroscopy was used to study the ionic conductivity of the SPE series in the temperature interval 30 degrees C-90 degrees C, and a battery device was constructed to evaluate a 25 wt% d(8)-PMMA electrolyte. The Li | SPE | LiFePO4 cell cycled at 60 degrees C, giving a discharge capacity of 120 mAh g(-1), while cyclic voltammetry showed that the SPE was stable at 60 degrees C.
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| 3. |
- Boujemaoui, Assya, et al.
(författare)
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SI-RAFT/MADIX polymerization of vinyl acetate on cellulose nanocrystals for nanocomposite applications
- 2016
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Ingår i: Polymer. - : Elsevier. - 0032-3861 .- 1873-2291. ; 99, s. 240-249
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, poly(vinyl acetate) grafted cellulose nanocrystals (CNC-g-PVAc) were prepared via surface initiated reversible addition-fragmentation chain transfer and macromolecular design via the interchange of xanthates (SI-RAFT/MADIX) polymerization. Successful grafting of PVAc from CNC was confirmed by FT-IR and TGA analysis. PVAc nanocomposites reinforced with CNC-g-PVAc, as well as pristine CNC for comparison, of different weight percentages (0.5, 1, 3 and 5 wt%) of CNC were prepared via solvent casting. The PVAc reinforced with CNC-g-PVAc resulted in higher transparency and improved mechanical properties compared with unmodified CNC nanocomposites. The addition of 5 wt% CNC-g-PVAc increased the modulus of neat PVAc with as much as 154%. The proposed SI-RAFT/MADIX on CNC could be applied to wide range of monomers, and it is believed to be an efficient and robust method for CNC functionalization, thus expanding the potential applicability of CNC.
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| 4. |
- Chang, B., et al.
(författare)
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Microstructure characterization in a single isotactic polypropylene spherulite by synchrotron microfocus wide angle X-ray scattering
- 2018
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Ingår i: Polymer. - : Elsevier. - 0032-3861 .- 1873-2291. ; 142, s. 387-393
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Tidskriftsartikel (refereegranskat)abstract
- Position-resolved microstructure in a single spherulite of iPP is quantitatively studied by synchrotron microfocus wide angle X-ray scattering. The results show that the normal of mother lamellae in a spherulite is aligned mainly perpendicular to the radius, and the subsidiary daughter lamellae are inclined 80.75° with respect to that of the dominant mother lamellae. The crystallinity in the spherulite is in the range of 46%–56%, which is rarely influenced by the crystallization temperature. The ratio between the daughter lamellae and the mother lamellae is 0.18 when iPP crystallizes at 138 °C and it decreases to 0.11 as the crystallization temperature is decreased to 130 °C. The b-axis and c-axis in the mother lamellae tend to orient perpendicular to the radius direction, and the a-axis prefers to align in the radius direction.
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| 5. |
- Gedde, Ulf W, et al.
(författare)
-
Richard Hays Boyd in memorial
- 2017
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Ingår i: Polymer. - : Elsevier. - 0032-3861 .- 1873-2291. ; 118, s. 305-306
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Tidskriftsartikel (refereegranskat)
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| 6. |
- Hassanzadeh, Salman, et al.
(författare)
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A proof-of-concept for folate-conjugated and quercetin-anchored pluronic mixed micelles as molecularly modulated polymeric carriers for doxorubicin
- 2015
-
Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 74, s. 193-204
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Tidskriftsartikel (refereegranskat)abstract
- Pluronic, F127 (PEG-PPO-PEG, Mn = 12,500 g/mol) and reverse pluronic, 10R5 (PPO-PEG-PPO, Mn = 2000 g/mol) were molecularly modulated to reach multifunctional mixed micelle systems aiming to overcome some of the inherent weaknesses of pluronic based drug delivery systems. Targeting function was introduced by covalent attachment of folic acid to F127 (F127-FA), while quercetin was anchored to 10R5 (P-Q). The successful syntheses were evidenced by H-1 NMR, FTIR, DSC and UV-Vis. The proof-of-concept for the mixed micelles prepared from the drug anchored pluronics was demonstrated through reduced CMCs, slower release rates and increased Doxorubicin (DOX) encapsulation capacity from similar to 19% to similar to 43%. Quercetin therefore boosted the interactions of DOX with the hydrophobic core of the micelles. This was further evidenced by colloidal probe AFM which demonstrated almost doubled adhesion forces between the DOX coated probe and the quercetin modified pluronic as compared to the plain pluronic. The pre-biological essay of the DOX-modulated mixed micelle demonstrates promising properties. In addition quercetin has previously been proposed as combinatory drug to DOX enhancing its therapeutic function and reducing the side effects to normal cells.
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| 7. |
- Kassa, Hailu G., et al.
(författare)
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Nano-mechanical properties of interphases in dynamically vulcanized thermoplastic alloy
- 2018
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Ingår i: Polymer. - : ELSEVIER SCI LTD. - 0032-3861 .- 1873-2291. ; 135, s. 348-354
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Tidskriftsartikel (refereegranskat)abstract
- We present a high-resolution study of the viscoelastic response of a thermoplastic alloy using a multi-frequency method called intermodulation atomic force microscopy. We quantitatively characterize the response in terms of calibrated dynamic force quadrature curves, showing the conservative and dissipative forces at each image pixel as functions of the oscillation amplitude for industrial polymer blends.
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| 8. |
- Kim, Young Yong, et al.
(författare)
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Synchrotron X-ray scattering and photon correlation spectroscopy studies on thin film morphology details and structural changes of an amorphous-crystalline brush diblock copolymer
- 2016
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 105, s. 472-486
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Tidskriftsartikel (refereegranskat)abstract
- We investigated structural details and temperature-induced structural changes of an amorphous-crystalline brush diblock copolymer, poly(3-((6-((7-(9H-carbazol-9-yl)heptanoyl)oxy)hexyl)thio)propylglycidyl ether)(60)-b-poly(glycidyl 12-((3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl)oxy)-12oxododecanoate)(20) (PGK(60)-PGF(20)) in nanoscale thin films using synchrotron grazing incidence X-ray scattering (GIXS) and X-ray photon correlation spectroscopy (XPCS). Interestingly, the diblock copolymer was found to form a mixture of two different hexagonal cylinder structures (HEX1 and HEX2) where the PGF cylinders were aligned in the film plane. HEX1 was composed of PGF cylinders with higher population of crystals while HEX2 consisted of PGF cylinders with lower population of crystals. Surprisingly, the PGF block chains favorably self-assembled because of strong lateral interactions in the bristles, forming vertical multibilayer structure with partial interdigitation even in the highly confined cylindrical geometry. In heating run up to 340 K, some fraction of HEX2 was transformed to HEX1 via cold crystallization. In contrast, HEX1 was transformed to HEX2 above 340 K because of melting of the PGF crystals. The XPCS analysis found that the HEX structural changes associated with the cold crystallization in the PGF cylinder domains took place with relatively fast dynamics. The HEX structural changes associated with melting of the PGF crystals in the cylinder domains occurred with relatively slow dynamics; this unusual dynamics of structural changes might be attributed to a high energy melting process of PGF crystals against strong lateral interactions of the bristles.
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| 9. |
- Kocherbitov, Vitaly, et al.
(författare)
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Enthalpy of sorption by glassy polymers
- 2019
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Ingår i: Polymer. - : Elsevier. - 0032-3861 .- 1873-2291. ; 174, s. 33-37
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Tidskriftsartikel (refereegranskat)abstract
- Thermodynamics and molecular mechanisms of sorption of gases and liquids by glassy polymers and are still not fully understood. In particular, the enthalpy of sorption (or mixing) in the glassy state – a parameter crucial for understanding the thermodynamics of sorption is not properly described by existing approaches. In this work, we propose a thermodynamic theory that describes the effect of the glass transition on the enthalpy of sorption. Firstly, a rigorous thermodynamic expression for the sorption enthalpy is presented, and then equations applicable for practical calculations are derived using certain approximations. The theory presented here is tested on the experimental water sorption data on starch and cellulose. The equations describing the hydration enthalpy are in excellent agreement with experimental data. Remarkably, the glass transition-induced apparent heat capacity change for water in carbohydrate polymers turned out to be negative. Being counterintuitive, this result can however be supported by re-evaluation of the literature data on heat capacities of the starch-water system.
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| 10. |
- Mindemark, Jonas, et al.
(författare)
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Copolymers of trimethylene carbonate and epsilon-caprolactone as electrolytes for lithium-ion batteries
- 2015
-
Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 63, s. 91-98
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Tidskriftsartikel (refereegranskat)abstract
- Random copolymers of trimethylene carbonate (TMC) and epsilon-caprolactone (CL) were synthesized through bulk ring-opening polymerization for use as host materials for solid polymer electrolytes. Amorphous electrolytes were solution-cast from the copolymers together with LiTFSI salt and showed lower T-g and higher ionic conductivity as the CL content was increased. The best-performing electrolyte, with a TMC:CL ratio of 60:40 with 28 wt% of LiTFSI, was found to have a conductivity of 1.6 x 10(-5) S cm(-1) at 60 degrees C (7.9 x 10(-7) S cm(-1) at 25 degrees C) and a T-g of -26 degrees C. This electrolyte was used in all-solid-state LiFePO4 half-cells that showed high capacity and coulombic efficiency at rates up to and including C/5.
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| 11. |
- Moyassari, Ali, et al.
(författare)
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Molecular dynamics simulation of linear polyethylene blends : Effect of molar mass bimodality on topological characteristics and mechanical behavior
- 2019
-
Ingår i: Polymer. - : ELSEVIER SCI LTD. - 0032-3861 .- 1873-2291. ; 161, s. 139-150
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Tidskriftsartikel (refereegranskat)abstract
- Blending different molar mass fractions of polyethylene (PE) in order to obtain materials with higher fracture toughness has previously proven beneficial. Our approach has been to use coarse-grained (CG) molecular dynamics (MD) simulations to obtain semicrystalline polyethylene systems on a nanoscale, and then draw them in order to mimic tensile testing. 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 low molar mass fraction disentangled to a greater degree and ended up with a lower entanglement density than the high molar mass fraction, although the tie chain concentration was higher for the low molar mass fraction. The deformation behavior of semicrystalline PE above its glass transition temperature was then assessed in a uniaxial tensile deformation simulation. The low-strain mechanical properties (i.e. elastic modulus, yield stress and strain) were in accordance with the literature. The high-strain mechanical features and toughness were improved in bimodal systems. The presence of a high molar mass fraction in bimodal systems was shown to affect the crystallinity and tie chain concentration during the strain hardening, leading to tougher model systems. Finally, the bimodal system with equal shares of the molar mass fractions showed the highest toughness and the best ultimate mechanical properties while having a concentration of tie chains and entanglements intermediate between the values for the other systems. This was a clear sign of the non-exclusive role of tie chains and entanglements in the mechanical behavior of bimodal PE and more generally of semicrystalline polymers at high strains.
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| 12. |
- Moyassari, Ali, et al.
(författare)
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Simulation of semi-crystalline polyethylene : Effect of short-chain branching on tie chains and trapped entanglements
- 2015
-
Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 72, s. 177-184
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Tidskriftsartikel (refereegranskat)abstract
- A Monte-Carlo simulation method for assessing the tie chain and trapped entanglement concentration in linear polyethylene was extended to enable the simulation of explicitly branched polyethylene. A subroutine was added to the model making possible the incorporation of different branch lengths and distributions. In addition, the microstructure of branched polyethylene was considered to be made of lamellar stacks of different thicknesses, acknowledging the segregation phenomenon during crystallization. Also, based on complete exclusion of bulky branches from the crystal lattice, a 'pull-out' mechanism was developed for the relaxation of branched parts of polyethylene chains in the vicinity of the crystal layer. Simulations of two series of real polyethylene samples showed the effect of short-chain branching on the concentrations of tie chains and trapped entanglements. Introducing a few branches to an unbranched polyethylene increased the concentration of inter-lamellar connections significantly. This effect decayed if the number of branches was further increased. The tracking of the position of all the carbon atoms during the crystallization process was implemented in the model, making the average square end-to-end distance < r(2) > of polyethylene chains calculable. Simulation of chains with the same molar mass but with different branch contents showed a reduction in the average end-to-end distance with increased branching. The use of real molar mass distribution data was also added to the model features.
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| 13. |
- Nadiv, R., et al.
(författare)
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Polymer nanocomposites : Insights on rheology, percolation and molecular mobility
- 2018
-
Ingår i: Polymer. - : Elsevier Ltd. - 0032-3861 .- 1873-2291. ; 153, s. 52-60
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Tidskriftsartikel (refereegranskat)abstract
- The integration of carbon nanotubes (CNTs) into a polymer matrix strongly affects the rheological behavior that in turn may hamper the overall performance of the resulting composite. Research in this topic has focused on bulk rheological properties, while here we employ NMR diffusion experiments to explore the mobility (diffusivity) of epoxy molecules when loaded with CNTs. Rheology and light microscopy indicate percolation of CNT aggregates. Those aggregates cage a substantial amount of epoxy molecules while small angle X-ray scattering indicates some rearrangement of epoxy molecules in the vicinity of the nanotubes. NMR diffusion experiments distinguish between the slow diffusion of the caged molecules and that of the free ones, and relate the fraction of the former to the macroscopic system viscosity. The demonstrated surface-induced slowing-down of diffusion is attributed to strong intermolecular π-π interactions among the epoxy molecules, and between them and the CNT surface. These findings demonstrate the utility of NMR diffusion experiments as an additional method applied to nanocomposites.
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| 14. |
- Olsson, Pär A T, 1981-, et al.
(författare)
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All-atomic and coarse-grained molecular dynamics investigation of deformation in semi-crystalline lamellar polyethylene
- 2018
-
Ingår i: Polymer. - : Elsevier Ltd. - 0032-3861 .- 1873-2291. ; 153, s. 305-316
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Tidskriftsartikel (refereegranskat)abstract
- In the present work we have performed classical molecular dynamics modelling to investigate the effects of different types of force-fields on the stress-strain and yielding behaviours in semi-crystalline lamellar stacked linear polyethylene. To this end, specifically the all-atomic optimized potential for liquid simulations (OPLS-AA) and the coarse-grained united-atom (UA) force-fields are used to simulate the yielding and tensile behaviour for the lamellar separation mode. Despite that the considered samples and their topologies are identical for both approaches, the results show that they predict widely different stress-strain and yielding behaviours. For all UA simulations we obtain oscillating stress-strain curves accompanied by repetitive chain transport to the amorphous region, along with substantial chain slip and crystal reorientation. For the OPLS-AA modelling primarily cavitation formation is observed, with small amounts of chain slip to reorient the crystal such that the chains align in the tensile direction. This force-field dependence is rooted in the lack of explicit H-H and C-H repulsion in the UA approach, which gives rise to underestimated ideal critical resolved shear stress. The computed critical resolved shear stress for the OPLS-AA approach is in good agreement with density functional theory calculations and the yielding mechanisms resemble those of the lamellar separation mode. The disparate energy and shear stress barriers for chain slip of the different models can be interpreted as differently predicted intrinsic activation rates for the mechanism, which ultimately are responsible for the observed diverse responses of the two modelling approaches. © 2018 Elsevier Ltd
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| 15. |
- Olsson, Pär, et al.
(författare)
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Ab initio and classical atomistic modelling of structure and defects in crystalline orthorhombic polyethylene : Twin boundaries, slip interfaces, and nature of barriers
- 2017
-
Ingår i: Polymer. - : Elsevier Ltd. - 0032-3861 .- 1873-2291. ; 121, s. 234-246
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Tidskriftsartikel (refereegranskat)abstract
- We study the stability of twin boundaries and slip in crystalline orthorhombic polyethylene by means of density functional theory (DFT), using a nonempirical, truly nonlocal density function, and by means of classical molecular dynamics (MD). The results show that, in accordance with experimental observations, there is a clear preference to chain slip over transverse slip for all considered slip planes. The activation energy for pure chain slip lies in the range 10–20 mJ/m2 while that for transverse slip corresponds to 40–280 mJ/m2. For the (11¯0)-slip plane the energy landscape is non-convex with multiple potential energy minima, indicating the presence of stable stacking faults. This suggests that dissociation of perfect dislocations into partials may occur. For the two low-energy twin boundaries considered in this work, {110} and {310}, we find that the former is more stable than the latter, with ground state energies corresponding to 8.9 and 28 mJ/m2, respectively. We have also evaluated how well the empirical MD simulations with the all-atom optimized potential for liquid MD simulations (OPLS-AA) and the coarse-grained united atom (UA) potential concur with the DFT results. It is found that an all-atom potential is necessary to partially capture the γ-surface energy landscapes obtained from the DFT calculations. The OPLS-AA predicts chain slip activation energies comparable with DFT data, while the transverse slip energy thresholds are low in comparison, which is attributed to weak close ranged monomer repulsion. Finally, we find that the H-H interaction dominates the slip activation. While not explicitly represented in the UA potential, its key role is revealed by correlating the DFT energy landscape with changes in the electron distributions and by MD simulations in which components of the OPLS-AA intermolecular potential are selectively silenced. © 2017 Elsevier Ltd
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| 16. |
- Poveda-Reyes, Sara, et al.
(författare)
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Injectable composites of loose microfibers and gelatin with improved interfacial interaction for soft tissue engineering
- 2015
-
Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 74, s. 224-234
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Tidskriftsartikel (refereegranskat)abstract
- Poly(L-lactic acid) (PLLA) microfibers were surface functionalized by graft photopolymerization of 2-hydroxyethyl methacrylate (HEMA) onto the fiber surface. Grafted fibers were easily dispersed in enzymatically gelling tyramine-substituted gelatin, forming a homogeneous dispersion without hindering subsequent gelatin crosslinking. The obtained injectable hydrogels showed improved mechanical properties compared to analogues based on non-modified fibers. The composite with 1% (w/v) of surface modified fibers had a three-fold higher shear storage modulus (535.2 +/- 90 Pa) than pure gelatin (184.9 +/- 32 Pa) while no significant increase was observed in the case of non-grafted fiber composites. Moreover, PHEMA grafting on PLLA fibers did not compromise cell viability and proliferation within the hydrogel. The new injectable hydrogels offer improved potential as substrates for the regeneration of soft tissues.
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| 17. |
- Sigolaeva, Larisa, et al.
(författare)
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Long-term stable poly(ionic liquid)/MWCNTs inks enable enhanced surface modification for electrooxidative detection and quantification of dsDNA
- 2019
-
Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 168, s. 95-103
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Tidskriftsartikel (refereegranskat)abstract
- This work demonstrates the use of imidazolium-based poly(ionic liquid)s (PILs) as efficient dispersants of multiwalled carbon nanotubes (MWCNTs). With these polymeric dispersants, highly stable fine dispersions of MWCNTs (inks) can be easily prepared in aqueous media and applied for rather simple but efficient surface modification of screen-printed electrodes (SPEs). Such a modification of SPEs remarkably increases the electroactive surface area and accelerates the electron transfer rate due to synergistic combination of specific features of MWCNTs such as strong adsorptive property and high specific surface with the advantages of PILs like ion conductivity and dispersability. We further show that the PIL/MWCNT-modified SPEs can be beneficially utilized for direct electrochemical analysis of double stranded DNA (dsDNA). Specifically, it is exemplified by the direct electrooxidation of guanine and adenine bases in salmon testes dsDNA chosen as a model system. The linear ranges for the determination of dsDNA correspond to 5-500 mu g/mL for the oxidative peak of guanine and 0.5-50 mu g/mL for the oxidative peak of adenine. This makes direct electrochemical dsDNA detection with the use of the easy-preparable PIL/MWCNT-modified SPEs strongly competing to currently applied spectral and fluorescent techniques. Furthermore, we show that the developed constructs are capable of sensing a single point mutation in the 12-bases single-stranded DNA fragments. Such detection is of high clinical significance in choosing an adequate anticancer treatment, where the electrochemical identification of the point mutation could offer time and cost benefits.
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| 18. |
- Sundberg, Johan, 1982, et al.
(författare)
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Controlled molecular reorientation enables strong cellulose fibers regenerated from ionic liquid solutions
- 2015
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 75, s. 119-124
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose is difficult to solubilize and undergoes thermal decomposition prior to melting. In recent years ionic liquids have been evaluated as solvents of cellulose. In the regeneration process the non-solvent governs the resulting material's crystallinity. Water adsorbs to amorphous cellulose, acts as plasticizer and lowers the Tg, hence the degree of crystallinity will affect the potential strain induced reorientation. We prepared regenerated cellulose fibers form ionic liquid using different non-solvents. The influence of shear forces upon cellulose chain alignment during extrusion was simulated in silica based upon rheological measurements. The regenerated fibers had different physical, morphological and mechanical properties. Molecular re-orientation in fibers induced by mechanical strain, at humidities above the Tg, resulted in much improved mechanical properties with the Young's modulus reaching 23.4 ± 0.8 GPa and the stress at break 504.6 ± 51.9 MPa, which is comparable to commercially available cellulose fibers.
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| 19. |
- Undin, Jenny, et al.
(författare)
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Controlled copolymerization of the functional 5-membered lactone monomer, alpha-bromo-gamma-butyrolactone, via selective organocatalysis
- 2016
-
Ingår i: Polymer. - : Elsevier. - 0032-3861 .- 1873-2291. ; 87, s. 17-25
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Tidskriftsartikel (refereegranskat)abstract
- The selective nature of organic catalysts has been exploited to synthesize copolymers of the functional monomer, alpha-bromo-gamma-butyrolactone (alpha Br gamma BL), with trimethylene carbonate (TMC), 2-allyloxymethyl-2ethyl- trimethylene carbonate (AOMEC) and epsilon-caprolactone (epsilon CL) with excellent control. The high control is attributed to high selectivity and reactivity at ambient reaction temperatures, which suppresses the degree of side reactions (e.g., transesterification) that inherently plague this class of co-monomers. In particular, good results were obtained using diphenyl phosphate (DPP) as a catalyst, resulting in copolymers with low dispersities (D-M) (i.e., approximately 1.08) and number average molecular weights (M-n) of approximately 20,000 g/mol. The high control opened the possibility to construct more complex polymeric structures, exemplified via the synthesis of a multifunctional triblock copolymer composed of AOMEC as the center block, flanked with a statistical copolymer consisting of 3CL and aBrgBL. The subsequent grafting of methyl acrylate (MA) via Cu(0)-mediated CRP on the copolymers resulted in graft copolymers with a final D-M of less than 1.2.
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| 20. |
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| 21. |
- Crassous, Jerome, et al.
(författare)
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Design of block copolymer micelles via crystallization
- 2015
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 62, s. 1-13
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Tidskriftsartikel (refereegranskat)abstract
- This Feature Article provides an overview of the progress made over the last few years in the design of diblock copolymer micelles based on crystallization-driven self-assembly (CDSA) towards the development of novel and fascinating morphologies with crystalline-cores. Here, we describe the different approaches employed in order to engineer a large variety of semicrystalline micellar architectures. We highlight kinetic strategies that have been employed to direct morphological transitions, which can then be further tuned thus increasing the range of possible micellar structures. We then emphasize the development of complex hybrid assemblies generated by taking advantage of the self-assembly process of crystalline-corona di-BCP micelles with colloidal particles. Each section introduces and emphasizes the potential applications of this class of nanomaterials. (C) 2015 Elsevier Ltd. All rights reserved.
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| 22. |
- Diaz, M., et al.
(författare)
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Thermophysical characterization of a reversible dynamic polymer network based on kinetics and equilibrium of an amorphous furan-maleimide Diels-Alder cycloaddition
- 2017
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 120, s. 176-188
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Tidskriftsartikel (refereegranskat)abstract
- The equilibrium and kinetics of the furan-maleimide Diels-Alder (DA) reaction for the formation of a reversible network were studied by calorimetry between 25 °C and 90 °C using an amorphous bismaleimide eliminating solvent use. The relationship between the equilibrium conversion xeq with temperature and the effect of dilution were simulated. The glass transition-conversion relationship of the reversible network was established. The thermophysical properties of the reversible network were linked to the kinetics and equilibrium of the DA system, and studied by dynamic mechanical analysis (DMA), dielectric analysis (DEA) and rheometry. Below Tg the reversible network behaves like an irreversible network; however, above Tg, a decrease in the rubber tensile storage modulus was observed due to a reduction of cross-link density caused by the retro DA reaction. DEA revealed that above Tg, an interface is formed between released bismaleimide molecules and the remaining network. The rheological behavior is related to xeq and the lifetime of the reversible covalent bonds. When xeq is higher than the gelation conversion xgel (below 90 °C), the system gels at constant xgel. An elastic strengthening effect is observed in a transition region between 90 °C and 115 °C. Above 115 °C the system is reaching a viscous melt behavior. These observations are important for the application of this network as a self-healing material and as a recyclable elastomer or thermoset.
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| 23. |
- Engqvist, Jonas, et al.
(författare)
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Measurement of multi-scale deformation of polycarbonate using X-ray scattering with in-situ loading and digital image correlation
- 2016
-
Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 82, s. 190-197
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Tidskriftsartikel (refereegranskat)abstract
- Deformation of amorphous, glassy polycarbonate (PC) is characterised over a wide range of length-scales using spatially-resolved wide angle X-ray scattering (WAXS) with simultaneous digital image correlation and in-situ uni-axial loading. Novel observations are presented on the correlation of the evolution of the molecular structure linked to the relevant local macroscopic measures of strain as the sample deforms. This provides new insights into the mechanisms of deformation in amorphous, glassy polymers. Strains and evolving anisotropy are observed, and quantified, at different length scales identified from the WAXS measurements connected to inter- and intramolecular structures. The intermolecular structures show permanent deformations in the form of unrecoverable stretches and reorientations, whilst intramolecular structures how recoverable strains and unrecoverable reorientations. Such insights pave the way for development of enhanced constitutive models for amorphous glassy polymers with a correct micro-mechanical basis and calibrated evolution of anisotropy.
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| 24. |
- Kádár, Roland, 1982, et al.
(författare)
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First normal stress difference and in-situ spectral dynamics in a high sensitivity extrusion die for capillary rheometry via the 'hole effect'
- 2016
-
Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 104:8, s. 193-203
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Tidskriftsartikel (refereegranskat)abstract
- The development of a high sensitivity polymer melt extrusion flow instability detection die capable of estimating the normal stress differences of polymer melts during capillary rheometry tests via the 'hole effect' is presented here as proof-of-principle. Two polymer melts, a low density polyethylene (branched topology) and a high density polyethylene (linear topology), were tested in a variety of experimental configurations with the purpose of determining optimal conditions for performing normal stress difference measurements. The data was compared with rotational rheometry oscillatory shear measurements analyzed via the Laun rule. It is shown that it is possible to estimate the first normal stress difference in the capillary die, whereas the second normal stress difference cannot be determined within the experimental errors using the current configuration design. Furthermore, the influence of the induced streamline curvature via the 'hole effect' on the onset and development of melt flow instabilities is simultaneously assessed. It is shown that the hole depth has a stabilizing influence, i.e. the onset of instabilities occurs at higher shear rates, in the long chain branched polymer tested, whereas for the linear polymer tested it has a destabilizing effect on the stick-slip instability i.e. the onset of stick-slip occurs at lower shear rates.
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| 25. |
- Larsson, Matilda, et al.
(författare)
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Effect of hydrophobically modified graphene oxide on the properties of poly(3-hydroxybutyrate-co-4-hydroxybutyrate)
- 2017
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 108, s. 66-77
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Tidskriftsartikel (refereegranskat)abstract
- Nanocomposites of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3,4HB)] and hydrophobically modified graphene oxide (GO) were prepared via melt blending and characterised with respect to processability, polymer degradation, as well as thermal, rheological and mechanical properties. GO prepared via the modified Hummer’s method was alkylated by reactions with butyl-, octyl- and hexadecylamine, respectively. The successful functionalisation was verified by IR spectroscopy, X-ray diffraction measurements, transmission electron microscopy and elemental analysis. The thermal decomposition temperature of the alkylated GOs increased with increasing alkyl chain length. Moreover, the alkylated GOs showed a much improved compatibility with P(3,4HB) in the melt compared to the unmodified GO, and microscopy showed an even distribution in the polymer matrix. The molecular weight of P(3,4HB) was found to decrease during the melt extrusion, and the chain degradation was found to increase after the addition of alkylated GO. However, this effect decreased with increasing alkyl chain length. Melt rheology measurements showed that percolating networks appeared at filler contents above ~2 wt%. These networks were detected as increases in shear storage modulus and decreased phase shifts towards more elastic materials over time and at low frequencies. During cooling of the melts, calorimetric measurements showed an increase in the crystallisation temperature and enthalpy with increasing filler contents up to ~2 wt%. However, at higher filler contents a decreased propensity for crystallisation was noted, which again indicated network formation. Tensile testing showed that the nanocomposites containing the GO with hexadecyl chains displayed the highest elongation at break and yield stress. However, the numbers were lower compared to the unfilled P(3,4HB), most probably because of the lower molecular weight of the P(3,4HB) in the nanocomposites. The results of the present study demonstrated that alkylation of GO greatly improves the compatibility with the polymer, and that the processability and thermo-mechanical properties of the nanocomposites are systematically influenced by the GO content and the alkyl chain length.
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| 26. |
- Leone, G., et al.
(författare)
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Polyolefin thermoplastic elastomers from 1-octene chain-walking polymerization
- 2016
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 100, s. 37-44
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Tidskriftsartikel (refereegranskat)abstract
- This work reports the polymerization of 1-octene to yield semicrystalline, branched poly(ethylene) like materials with high molecular weight and narrow molecular weight distribution. The polymerization of 1-octene was catalyzed by an alpha-diimine Ni(II) complex [(ArN)C(CH3)-(CH3) C(NAr)]NiBr2 [Ar = 2,6-(iPr)(2)C6H3], in combination with different aluminum alkyls, i.e., Et2AlCl, MAO and MMAO. The effect of the aluminum alkyl, monomer concentration, polymerization temperature and Al/Ni ratio on the activity, selectivity of monomer insertion, polymers microstructure, and structure/properties is investigated. The results indicate the possibility to tune the polymer microstructure, which in turn strongly affects the structure, thermal and mechanical polymer properties. Mechanical testing carried out by uniaxial stretching until failure and step-cycle tensile experiments served to establish these materials as a new class of polyolefin thermoplastic elastomers with different performances depending on the microstructure and crystallinity.
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| 27. |
- Li, Joaquim, et al.
(författare)
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Equation of state of PEG/PEO in good solvent. Comparison between a one-parameter EOS and experiments
- 2015
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 80, s. 205-213
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Tidskriftsartikel (refereegranskat)abstract
- We investigate, through osmotic pressure measurements, the validity of the single-parameter equation of state (EOS) for solutions of polyethylene glycols in water, by Cohen et al. 1,2 We show that it is physically meaningful and that a reasonable good correspondence between the osmotic pressures for PEG35 in large range of concentrations is obtained. We also take the chain length dependence into account in our analysis, as suggested by Cohen et al. By recalculating the experimental pressures in the paper by Jönsson et al. 3 applying the new calibration curve, which is based on the experimental results obtained in this study and the EOS obtained by Cohen et al., there is almost a perfect correspondence between the simulations and the experiments. These results have implications for correctly probing macromolecular interactions in wide range of systems when applying the osmotic stress method.
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| 28. |
- Li, Qianjin, et al.
(författare)
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Synthesis of fluorescent molecularly imprinted nanoparticles for turn-on fluorescence assay using one-pot synthetic method and a preliminary microfluidic approach
- 2018
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 138, s. 352-358
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Tidskriftsartikel (refereegranskat)abstract
- Fluorescent molecularly imprinted polymers (MIPs) have received considerable attention for their promising applications in sensing, imaging and diagnostics. Different synthetic methods have been reported to prepare fluorescent MIPs. Here, one-pot polymerization method was developed to synthesize fluorescent MIP nanoparticles (NPs) bearing a suitable fluorescent label as the fluorescence acceptor. The MIP NPs can emit strong fluorescence based on fluorescence resonance energy transfer (FRET) when they bind to analytes acting as the fluorescence donor. The one-pot synthetic method is straightforward, less time-consuming and easy to optimize the loading of fluorescence acceptor. Additionally, a preliminary microfluidic reactor was designed for preparing such fluorescent MIP NPs with more uniform size in a continuous process for the first time. The fluorescent MIP NPs can be used for selective detection of the analytical target in a FRET-based turn-on fluorescence assay which is easy to carry out with no tedious separation steps.
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| 29. |
- Mauri, Massimiliano, 1987, et al.
(författare)
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Crosslinking of an ethylene-glycidyl methacrylate copolymer with amine click chemistry
- 2017
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 111, s. 27-35
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Tidskriftsartikel (refereegranskat)abstract
- Commonly used crosslinking methods for polyethylenes result in the release of harmful by-products. Here, we demonstrate that an epoxy-bearing polyethylene copolymer, which contains 8 wt% glycidyl methacrylate, can be efficiently crosslinked without by-product formation. Click chemistry based on multifunctional amine curing agents, which carry at least two functional groups separated by a flexible spacer, was used to prepare thermosets. Compounding of the crosslinker and copolymer through extrusion at 120 °C could be carried out without onset of the curing reactions. Careful adjustment of the curing time and temperature, ranging from 20 to 120 min and 160–200 °C, resulted in a high network density of at least 2.8 crosslinks per 1000 carbons at a curing agent stoichiometry of as little as 0.5 wt%.
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| 30. |
- Nederstedt, Hannes, et al.
(författare)
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Single-ion conducting polymer electrolytes with alternating ionic mesogen-like moieties interconnected by poly(ethylene oxide) segments
- 2019
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 177, s. 231-240
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Tidskriftsartikel (refereegranskat)abstract
- Solid single-Li+-ion conducting polymer electrolytes are currently explored for safe high-temperature lithium batteries. In the present work we have prepared and studied materials based on alternating mesogen-like naphthalene sulfonate units interconnected by flexible poly(ethylene oxide) (PEO) segments in order to induce microphase separation and physical crosslinking. These segmented polymers were readily prepared in polycondensations of a naphthalene diol sulfonate and chain-end chlorinated PEO. The ionic content of the final materials was conveniently controlled by using PEOs of different molecular weights. Analysis by X-ray scattering showed a morphology with nanoscopic domains of naphthalene sulfonate units dispersed in a matrix of amorphous PEO segments. The aggregation of the naphthalene sulfonate units increased with temperature up to at least 100 °C, while the crystallization of the PEO segments in some materials reversibly dissolved the naphthalene sulfonate domains upon cooling. The crystallinity decreased and the glass transition temperature increased with decreasing PEO segment length, i.e., increasing in ionic content, because of increasing ionic coordination and a decreasing PEO segment length in-between the naphthalene sulfonate domains. At 80 and 120 °C, the present single-Li+-ion conductors reached conductivities up to 1.4·10−6 and 5.5·10−6 S cm−1, respectively, which after addition of 29 wt % triglyme increased to 2.9·10−6 and 8.2·10−6 S cm−1, respectively. The combined results showed that the macromolecular design with ionic mesogen-like units that form stable physically cross-linked morphologies by interconnecting flexible polyether segments is advantageous for polymer electrolytes for safe high-temperature operation.
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| 31. |
- Pérez-Tamarit, S., et al.
(författare)
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In-situ understanding of pore nucleation and growth in polyurethane foams by using real-time synchrotron X-ray tomography
- 2019
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 166, s. 50-54
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Tidskriftsartikel (refereegranskat)abstract
- The nucleation and growth of pores in PU foams have been visualized and quantified for the first time in 4D using in-situ tomographic microscopy. Acquiring sequences of 3D images in 156 ms each, we describe homogeneous and heterogeneous nucleation and subsequent bubble growth dynamics for materials with and without nucleating nanoparticles. Exploiting the time resolved tomographic sequences we obtained the bubble nucleation rate, bubble density and size evolution, based on which the diffusion coefficient of gas molecules in polymer can be calculated, evidencing the reduction of diffusivity provoked by the inclusion of nanoparticles. We found that nucleation and growth are in a large extend decoupled in time.
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| 32. |
- Riazi, Kamran, et al.
(författare)
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Polystyrene comb architectures as model systems for the optimized solution electrospinning of branched polymers
- 2016
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 104:8, s. 240-250
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Tidskriftsartikel (refereegranskat)abstract
- The bead to bead-free fibers transition for electrospun filaments was investigated for well-defined linear and comb homopolymers. A series of monodisperse model comb structures with well-defined backbone and side chains was synthesized using anionic polymerization of polystyrene (PS). All model combs had the same backbone and a similar total molecular weight. The length and number of branches was varied, but the total number of monomers in the side chains was nearly constant.Solutions of these polystyrenes in N,N-dimethylformamide (DMF) were electrospun under identical conditions to determine the effect of molecular topology on the morphology of the fibers. The morphology and fiber diameter for all PS model polymers depended on the zero shear viscosity, η0. The comb solutions generally formed fibers at lower η0 and the fibers had larger diameters compared with linear polystyrene. The bead to fiber transition occurred at substantially lower polymer concentrations for combs with fewer, but longer branches.
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| 33. |
- Schoch, Rafael L., et al.
(författare)
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Protein exclusion is preserved by temperature sensitive PEG brushes
- 2017
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 132, s. 362-367
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Tidskriftsartikel (refereegranskat)abstract
- Poly(ethylene glycol) (PEG) is widely used in biotechnology-related applications yet its temperature-dependent functionality is not well understood. Here, we use bovine serum albumin (BSA) monomers and cross-linked dimers to directly probe the height of strongly stretched PEG brushes using surface plasmon resonance (SPR) in aqueous solution. Our results show that PEG brush height follows a smooth decrease as a function of increasing temperature commencing near room temperature. Measurements obtained by BSA monomers and dimers are comparable and suggest that BSA effectively probes the leading edge of the brush with minimal penetration into its interior being supported by SPR reflectivity calculations. Further, the BSA-PEG interaction remains largely inert over the entire temperature range. Overall, PEG brushes undergo a smooth conformational transition while fully preserving its protein excluding properties far from the lower critical solution temperature.
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| 34. |
- Xie, Fei, et al.
(författare)
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A simple and versatile implicit solvent model for polyethylene glycol in aqueous solution at room temperature
- 2016
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 84, s. 132-137
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Tidskriftsartikel (refereegranskat)abstract
- We present a very simple polymer model of polyethylene glycols/oxides in water that can be used in combination with Molecular Dynamics or Monte Carlo simulations to accurately reproduce the equation of state and radii of gyrations across several orders of magnitude, in terms of osmotic pressure and polymer length. This is of importance for example in osmotic stress experiments, with the aim to accurately probe macromolecular interactions, although the polymer model may prove useful in many other scenarios as well. It is constructed in a manner that makes it straightforward to treat by classical density functional theory, which should facilitate theoretical studies of model systems with explicit polymers of realistic lengths and concentrations. The polymer model is validated by comparisons with experiments and a single-parameter equation of state by Cohen et al. From a computational perspective, we recommend Metropolis Monte Carlo simulations in the low concentration regime, whereas Molecular Dynamics simulations are preferable in the more concentrated systems, at least if one has access to computer clusters. (C) 2015 Elsevier Ltd. All rights reserved.
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