233 research outputs found
Phase Behavior of Polyelectrolyte Block Copolymers in Mixed Solvents
We have studied the phase behavior of the poly(n-butyl
acrylate)-b-poly(acrylic acid) block copolymer in a mixture of two miscible
solvents, water and tetrahydrofuran (THF). The techniques used to examine the
different polymers, structures and phases formed in mixed solvents were static
and dynamic light scattering, small-angle neutron scattering, nuclear magnetic
resonance and fluorescence microscopy. By lowering the water/THF mixing ratio
X, the sequence unimers, micron-sized droplets, polymeric micelles was
observed. The transition between unimers and the micron-sized droplets occurred
at X = 0.75, whereas the microstructuration into core-shell polymeric micelles
was effective below X = 0.4. At intermediate mixing ratios, a coexistence
between the micron-sized droplets and the polymeric micelles was observed.
Combining the different aforementioned techniques, it was concluded that the
droplet dispersion resulted from a solvent partitioning that was induced by the
hydrophobic blocks. Comparison of poly(n-butyl acrylate) homopolymers and
poly(n-butyl acrylate)-b-poly(acrylic acid) block copolymers suggested that the
droplets were rich in THF and concentrated in copolymers and that they were
stabilized by the hydrophilic poly(acrylic acid) moieties.Comment: 11 pages, 12 figures, to appear in Macromolecule
Interfaces in Diblocks: A Study of Miktoarm Star Copolymers
We study AB miktoarm star block copolymers in the strong segregation
limit, focussing on the role that the AB interface plays in determining the
phase behavior. We develop an extension of the kinked-path approach which
allows us to explore the energetic dependence on interfacial shape. We consider
a one-parameter family of interfaces to study the columnar to lamellar
transition in asymmetric stars. We compare with recent experimental results. We
discuss the stability of the A15 lattice of sphere-like micelles in the context
of interfacial energy minimization. We corroborate our theory by implementing a
numerically exact self-consistent field theory to probe the phase diagram and
the shape of the AB interface.Comment: 12 pages, 11 included figure
Bespoke cationic nano-objects via RAFT aqueous dispersion polymerisation
A range of cationic diblock copolymer nanoparticles are synthesised via polymerisation-induced self-assembly (PISA) using a RAFT aqueous dispersion polymerisation formulation. The cationic character of these nanoparticles can be systematically varied by utilising a binary mixture of two macro-CTAs, namely non-ionic poly(glycerol monomethacrylate) (PGMA) and cationic poly[2-(methacryloyloxy)ethyl]trimethylammonium chloride (PQDMA), with poly(2-hydroxypropyl methacrylate) (PHPMA) being selected as the hydrophobic core-forming block. Thus a series of cationic diblock copolymer nano-objects with the general formula ([1 - n] PGMAx + [n] PQDMAy) - PHPMAz were prepared at 20% w/w solids, where n is the mol fraction of the cationic block and x, y and z are the mean degrees of polymerisation of the non-ionic, cationic and hydrophobic blocks, respectively. These cationic diblock copolymer nanoparticles were analysed in terms of their chemical composition, particle size, morphology and cationic character using 1H NMR spectroscopy, dynamic light scattering (DLS), transmission electron microscopy (TEM), and aqueous electrophoresis, respectively. Systematic variation of the above PISA formulation enabled the formation of spheres, worms or vesicles that remain cationic over a wide pH range. However, increasing the cationic character favors the formation of kinetically-trapped spheres, since it leads to more effective steric stabilisation which prevents sphere-sphere fusion. Furthermore, cationic worms form a soft free-standing gel at 25 °C that undergoes reversible degelation on cooling, as indicated by variable temperature oscillatory rheology studies. Finally, the antimicrobial activity of this thermo-responsive cationic worm gel towards the well-known pathogen Staphylococcus aureus is examined via direct contact assays
Galactose-α-1,3-Galactose–Specific IgE Is Associated with Anaphylaxis but Not Asthma
Rationale: IgE antibodies to the mammalian oligosaccharide galactose-α-1,3-galactose (α-gal) are common in the southeastern United States. These antibodies, which are induced by ectoparasitic ticks, can give rise to positive skin tests or serum assays with cat extract
Solution Properties of 1,3-Cyclohexadiene Polymers by Laser Light Scattering and Small-Angle Neutron Scattering
Mesostructured Block Copolymer Nanoparticles: Versatile Templates for Hybrid Inorganic/Organic Nanostructures
We present a versatile strategy to prepare a range of nanostructured poly(styrene)-block-poly(2-vinyl pyridine) copolymer particles with tunable interior morphology and controlled size by a simple solvent exchange procedure. A key feature of this strategy is the use of functional block copolymers incorporating reactive pyridyl moieties which allow the absorption of metal salts and other inorganic precursors to be directed. Upon reduction of the metal salts, well-defined hybrid metal nanoparticle arrays could be prepared, whereas the use of oxide precursors followed by calcination permits the synthesis of silica and titania particles. In both cases, ordered morphologies templated by the original block copolymer domains were obtained
On the Mechanism of Shear Induced Texture Changes in Cholesterics-Electric Field Effects
Physical Properties of Dendritic Macromolecules: A Study of Glass Transition Temperature
The variation of glass transition temperature with molecular weight and chain-end composition for dendritic polyethers and polyesters was studied. A new and modified version of the chain-end free volume theory was derived to account for the large number of chain ends in these unusual structures. For both homopolymers and a variety of novel block copolymers, the experimental variation in T with molecular weight was found to correlate well with theoretical predictions, thus demonstrating the wide applicability of the chain-end free volume theory. The glass transition was found to be greatly affected by the nature of the chain ends and internal monomer units
Effect of corona discharge treatment of poly(ethylene terephthalate) on the adsorption characteristics of the fluorosurfactant Zonyl FSC as studied via ESCA and surface energy measurements
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