| 1. |
- Al-Manasir, Nodar, et al.
(författare)
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Effects of Temperature and pH on the Contraction and Aggregation of Microgels in Aqueous Suspensions
- 2009
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 113:32, s. 11115-11123
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Tidskriftsartikel (refereegranskat)abstract
- Chemically cross-linked poly(N-isopropylacrylamide) (PNIPAM) microgels and PNIPAM with different amounts of acrylic acid groups (PNIPAM-co-PAA) were synthesized and the temperature-induced aggregation behaviors of aqueous suspensions of these microgels were investigated mainly with the aid of dynamic light scattering (DLS) and turbidimetry. The DLS results show that the particles at all conditions shrink at temperatures up to approximately the lower critical solution temperature (LCST), but the relative contraction effect is larger for the microgels without acid groups or for microgels with added anionic surfactant (SDS). A significant depression of the cloud point is found in suspensions of PNIPAM with very low concentrations of SDS. The compression of the microgels cannot be traced from the turbidity results, but rather the values of the turbidity increase in this temperature interval. This phenomenon is discussed in the framework of a theoretical model. At temperatures above LCST, the size of the microgels without attached charged groups in a very dilute suspension is unaffected by temperature, while the charged particles (pH 7 and 11) continue to collapse with increasing temperature over the entire domain. In this temperature range, low-charged particles of higher concentration and particles containing acrylic acid groups at low pH (pH 2) aggregate, and macroscopic phase separation is approached at higher temperatures. This study demonstrates how the stabilization of microgels can be affected by factors such as polymer concentration, addition of ionic surfactant to particles without charged acid groups, amount of charged groups in the polymer, and pH.
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| 2. |
- Asad Ayoubi, Mehran, et al.
(författare)
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Lamellar Microdomains of Block-Copolymer-Based Ionic Supramolecules Exhibiting a Hierarchical Self-Assembly
- 2014
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 47:10, s. 3428-3435
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Tidskriftsartikel (refereegranskat)abstract
- Based on a parent diblock copolymer of poly(styrene)-b-poly(methacrylic acid), PS-b-PMAA, linear-b-amphiphilic comb (L-b-AC) ionic supramolecules [Soft Matter 2013, 9, 1540-1555] are synthesized in which the poly(methacrylate) backbone of the ionic supramolecular AC-block is neutralized by alkyl (Cn; n = 8, 12, and 16) trimethylammonium counterions (i.e., side chains) at various ion (pair) fractions X [i.e., counterion/side-chain grafting density; X = number of alkyl counterions (i.e., side chains) per acidic group of the parent PMAA block] these L-b-AC ionic supramolecules exhibit a spherical-in-lamellar hierarchical self-assembly. For these systems, (1) the effective Flory-Huggins interaction parameter between L- and AC-blocks chi'(Cn/x) was extracted, and (2) analysis of the lamellar microdomains showed that when there is an increase in X, alkyl counterion (i.e., side chain) length l(sc), or both, there is an increase in both the average interfacial area per block junction Sigma and the thickness of the microlayer of the AC-block d(Ac).
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| 3. |
- Asad Ayoubi, Mehran, et al.
(författare)
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Micro- and nanophase separations in hierarchical self-assembly of strongly amphiphilic block copolymer-based ionic supramolecules
- 2013
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 9:5, s. 1540-1555
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Tidskriftsartikel (refereegranskat)abstract
- By a selective complexation between different alkyltrimethylammonium amphiphiles (C8, C12 and C16) and three different diblock copolymer systems of poly(styrene)-b-poly(methacrylic acid) at various grafting densities X (X = number of alkyl chains per acidic group of the poly(methacrylic acid) PMAA block), a class of ionic supramolecules are successfully synthesized whose molecular architecture consists of a poly(styrene) PS block (Linear block) covalently connected to a strongly amphiphilic comb-like block (AmphComb block), i.e. Linear-b-AmphComb. In the melt state, these ionic supramolecules can show simultaneous microphase (between Linear and AmphComb blocks) and nanophase (within the AmphComb blocks) separations. This leads to the formation of various structure-in-structure two-scale hierarchical self-assemblies, including S-in-S-LL, S-in-S-BCC, S-in-C, S-in-L and C-in-L, where S, S-LL, S-BCC, C and L stand for spherical, spherical in liquid-like state, spherical in body-centered-cubic arrangement, cylindrical and lamellar, respectively. Synchrotron small angle X-ray scattering (SAXS) and crossed polarizers, together with SAXS modelling analysis, were used for a detailed structural study of the samples. The morphology of the microphase separated state was mapped out on 'master' microdomain morphology diagrams as a function of the volume fraction of the AmphComb blocks (Phi(AmphComb)) and the compositional window of each microdomain morphology was determined. It was observed that, (i) within samples based on the same parent diblock copolymer system, the occurrence of a specific microdomain morphology is only dependent on the value of Phi(AmphComb), regardless of the grafting density X and the length of the alkyl side-chains, and (ii) microdomain morphological boundaries occur at Phi(AmphComb) values of similar to 0.20 (S-LL/C and S-BCC/C) and similar to 0.28 (C/L). Finally, the specific influences of the strongly amphiphilic nature of the AmphComb blocks on the observed morphological and hierarchical behaviours of our system are discussed. For reference, stoichiometric strongly amphiphilic comb-like (AmphComb) ionic supramolecules, based on complexation between a homopolymer of PMAA and the various alkyltrimethylammonium amphiphiles, were prepared, which nanophase separated into S (C8) or C (C12 and C16) domains.
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| 4. |
- Asad Ayoubi, Mehran, et al.
(författare)
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Morphological Investigation of Polydisperse Asymmetric Block Copolymer Systems of Poly(styrene) and Poly(methacrylic acid) in the Strong Segregation Regime
- 2013
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Ingår i: Journal of Polymer Science. Part B, Polymer Physics. - : Wiley. - 0887-6266. ; 51:23, s. 1657-1671
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Tidskriftsartikel (refereegranskat)abstract
- Samples of compositionally (highly) asymmetric diblock copolymers and, also, mixtures of diblock and triblock copolymers (the latter obtained as end-coupling products of two diblock molecules of the mixture), composed of (a) monodisperse majority block(s) of poly(styrene) (PS) and a polydisperse minority block of poly(methacrylic acid) (PMAA), microphase separate into spherical PMAA microdomains, either in disordered liquid-like state or body-centered-cubic (BCC) arrangement, at various annealing temperatures T, in the strong segregation regime SSR. We found that (i) the microphase separated state is favored over an anticipated molecularly homogenous state, (ii) the spherical microdomain morphology (with BCC symmetry) is favored over an anticipated hexagonally packed cylindrical morphology, (iii) the extent of the dissolution of short PMAA blocks in the PS material can be quantified, (iv) the spherical microdomains are dilated, and (v) despite molecular-weight (and architectural) polydispersity, well-ordered BCC structures can be obtained. (c) 2013 Wiley Periodicals, Inc.
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| 5. |
- BAYATI, SOLMAZ, et al.
(författare)
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Mixed micelles of oppositely charged poly(N-isopropylacrylamide) diblock copolymers
- 2017
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Ingår i: Journal of Polymer Science, Part B: Polymer Physics. - : Wiley. - 0887-6266. ; 55:19, s. 1457-1470
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Tidskriftsartikel (refereegranskat)abstract
- Mixed micelle formation between two oppositely charged diblock copolymers that have a common thermosensitive nonionic block of poly(N-isopropylacrylamide) (PNIPAAM) has been studied. The block copolymer mixed solutions were investigated under equimolar charge conditions as a function of both temperature and total polymer concentrations by turbidimetry, differential scanning calorimetry, two-dimensional proton nuclear magnetic nuclear Overhauser effect spectroscopy (2D 1H NMR NOESY), dynamic light scattering, and small angle X-ray scattering measurements. Well-defined and electroneutral cylindrical micelles were formed with a radius and a length of about 3 nm and 35 nm, respectively. In the micelles, the charged blocks built up a core, which was surrounded by a corona of PNIPAAM chains. The 2D 1H NMR NOESY experiments showed that a minor block mixing occurred between the core blocks and the PNIPAAM blocks. By approaching the lower critical solution temperature of PNIPAAM, the PNIPAAM chains collapsed, which induced aggregation of the micelles.
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| 6. |
- Dédinaité, Andra, et al.
(författare)
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Friction in aqueous media tuned by temperature-responsive polymer layers
- 2010
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Ingår i: SOFT MATTER. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 6:11, s. 2489-2498
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Tidskriftsartikel (refereegranskat)abstract
- An atomic force microscope colloidal probe technique has been employed to probe normal and friction forces between silica surfaces coated with adsorbed layers of a diblock copolymer of the composition poly(N-isopropylacrylamide)(48)-block-poly(3-acrylamidopropyl)trimethyla mmonium chloride)(20), abbreviated PNIPAAM(48)-b-PAMPTMA(+)(20). The interactions between the PNIPAAM(48)-b-PAMPTMA(+)(20)-coated surfaces across a 0.1 mM NaCl (pH 6) solution at 25 degrees C are purely repulsive, due to a combination of steric and electrostatic double-layer forces. However, when the temperature is increased to 35 degrees C, and subsequently to 45 degrees C, an attractive force develops at short separations due to the unfavourable PNIPAAM-water interaction at these temperatures. The temperature-dependent polymer-water interaction has implications for the friction force between the layers. At 25 degrees C a frictional force that increases linearly with increasing load is observed once the surfaces are brought into close contact. At higher temperatures significantly higher friction forces appear as a consequence of attractive segment-segment interactions. Further, a clearly expressed hysteresis between friction forces encountered on loading and unloading is detected. Our results demonstrate that both normal and friction forces between surfaces can be controlled by temperature changes when temperature-responsive polymers are employed, and friction forces can be adjusted as required from low to high.
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| 7. |
- Du, Guanqun, et al.
(författare)
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Condensed Supramolecular Helices : The Twisted Sisters of DNA
- 2022
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Ingår i: Angewandte Chemie (International edition). - : Wiley. - 1521-3773. ; 61:4
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Tidskriftsartikel (refereegranskat)abstract
- Condensation of DNA helices into hexagonally packed bundles and toroids represents an intriguing example of functional organization of biological macromolecules at the nanoscale. The condensation models are based on the unique polyelectrolyte features of DNA, however here we could reproduce a DNA-like condensation with supramolecular helices of small chiral molecules, thereby demonstrating that it is a more general phenomenon. We show that the bile salt sodium deoxycholate can form supramolecular helices upon interaction with oppositely charged polyelectrolytes of homopolymer or block copolymers. At higher order, a controlled hexagonal packing of the helices into DNA-like bundles and toroids could be accomplished. The results disclose unknown similarities between covalent and supramolecular non-covalent helical polyelectrolytes, which inspire visionary ideas of constructing supramolecular versions of biological macromolecules. As drug nanocarriers the polymer-bile salt superstructures would get advantage of a complex chirality at molecular and supramolecular levels, whose effect on the nanocarrier assisted drug efficiency is a still unexplored fascinating issue.
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| 8. |
- Gjerde, Natalie Solfrid, et al.
(författare)
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Synthesis and Characterization of a Thermoresponsive Copolymer with an LCST-UCST-like Behavior and Exhibiting Crystallization
- 2023
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Ingår i: ACS Omega. - 2470-1343. ; 8:34, s. 31145-31154
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Tidskriftsartikel (refereegranskat)abstract
- In this work, the diblock copolymer methoxy-poly(ethylene glycol)-block-poly(ϵ-caprolactone) (MPEG-b-PCL) was synthesized with a block composition that allows this polymer in aqueous media to possess both an upper critical solution temperature (UCST) and a lower critical solution temperature (LCST) over a limited temperature interval. The value of the UCST, associated with crystallization of the PCL-block, depended on heating (H) or cooling (C) of the sample and was found to be CPUCSTH = 32 °C and CPUCSTC = 23 °C, respectively. The LCST was not affected by the heating or cooling scans; assumed a value of 52 °C (CPLCSTH = CPLCSTC). At intermediate temperatures (e.g., 45 °C), dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and cryogenic transmission electron microscopy (cryo-TEM) showed that the solution consisted of a large population of spherical core-shell particles and some self-assembled rodlike objects. At low temperatures (below 32 °C), differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS) in combination with SAXS disclosed the formation of crystals with a cylindrical core-shell structure. Cryo-TEM supported a thread-like appearance of the self-assembled polymer chains. At temperatures above 52 °C, incipient phase separation took place and large aggregation complexes of amorphous morphology were formed. This work provides insight into the intricate interplay between UCST and LCST and the type of structures formed at these conditions in aqueous solutions of MPEG-b-PCL diblock copolymers.
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| 9. |
- Kjøniksen, Anna-Lena, et al.
(författare)
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Novel transition behavior in aqueous solutions of a charged thermoresponsive triblock copolymer
- 2009
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Ingår i: Colloids and surfaces A: Physicochemical and engineering aspects. - : Elsevier BV. - 0927-7757. ; 333:1-3, s. 32-45
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Tidskriftsartikel (refereegranskat)abstract
- Turbidity, dynamic light scattering, and steady shear viscosity measurements have been performed under the influence of a temperature gradient (0.2 °C/min) on aqueous solutions of a newly prepared monodisperse low-molar-mass (Mw = 1.34 × 104) methoxy-poly(ethylene glycol)-block-poly(N-isopropylacrylamide)-block-poly(4-styrenesulfonic acid sodium) triblock copolymer (MPEG53-b-P(NIPAAM)54-b-P(SSS)4). The results on this charged triblock copolymer revealed a novel temperature-induced transition from micelles to intermicellar complexes and the formation of collapsed and charged structures at higher temperatures. These experimental methods gave similar transition peaks. Intensity light scattering experiments conducted at several fixed temperatures on solutions of the triblock copolymer disclosed similar transition peaks in the radius of gyration. Cryogenic transmission electron microscopy (Cryo-TEM) measurements on 1 wt% samples at different temperatures, disclosed the building up of association structures at the maximum of the intermediate transition peak, and the breaking down of interchain associations at high temperatures. In the presence of salt, the transition peak at intermediate temperatures was still visible but the formation of flocs at high temperatures was strengthened because of screening of the repulsive electrostatic interactions, and it is also possible that deteriorated solubility of the polymer plays a role. These findings show that even with a short-chain polymer the formed association structures can undergo a major temperature-induced transition from unimers–micelles–intermicellar complexes to collapsed structures. By comparing the heating and cooling cycles, hysteresis effects in the transition behavior were disclosed.
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| 10. |
- Lazzara, Giuseppe, et al.
(författare)
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On the formation of inclusion complexes at the solid/liquid interface of anchored temperature-responsive PNIPAAM diblock copolymers with γ-cyclodextrin
- 2017
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Ingår i: Colloid and Polymer Science. - : Springer Science and Business Media LLC. - 0303-402X .- 1435-1536. ; 295:8, s. 1327-1341
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Tidskriftsartikel (refereegranskat)abstract
- The thermal responsive behavior of adsorbed layers of diblock copolymers of poly(N-isopropylacrylamide) (PNIPAAM) and poly((3-acrylamidopropyl)trimethylammonium chloride) (PAMPTMA(+)) with γ-cyclodextrin (γ-CD) at the solid/liquid interface has been investigated using three in situ techniques: null ellipsometry, quartz–crystal microbalance with dissipation monitoring, and neutron reflectometry. The measurements provided information about the adsorbed amounts, the layer thickness, hydration and viscoelastic properties, and the interfacial structure and composition. The copolymers adsorb to silica with the cationic PAMPTMA(+) blocks sitting as anchors in a flat conformation and the PNIPAAM chains extending into the solution. The copolymer system alone exhibits reversible collapse above the lower critical solution temperature of PNIPAAM. The addition of γ-CD to pre-adsorbed copolymer layers results in a highly extended conformation as well as some loss of copolymer from the surface, which we discuss in terms of the formation of surface-invoked lateral steric repulsion of formed inclusion complexes.
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