A new morpholine-functionalised, trithiocarbonate-based RAFT agent, MPETTC, was synthesised with an overall yield of 80% and used to prepare a poly(glycerol monomethacrlyate) (PGMA) chain transfer agent. Subsequent chain extension with 2-hydroxypropyl methacrylate (HPMA) using a RAFT aqueous dispersion polymerisation formulation at pH 7.0 7.5 resulted in the formation of morpholine-functionalised PGMA-PHPMA diblock copolymer worms via polymerisation-induced selfassembly (PISA). These worms form soft, free-standing aqueous hydrogels at 15% w/w solids. Acidification causes protonation of the morpholine end-groups at pH 3, which increases the hydrophilic character of the PGMA stabiliser block.This causes a subtle change in the copolymer packing parameter which induces a worm-to-sphere morphological transition and hence leads to in situ degelation. This order-order transition was characterised by dynamic light scattering (DLS), transmission electron microscopy (TEM) and gel rheology studies. On returning to pH 7, regelation is observed at 15% w/w solids, indicating the reversible nature of the transition. However, such diblock copolymer worm gels remain intact when acidified in the presence of electrolyte, since the cationic surface charge arising from the protonated morpholine end-groups is screened under these conditions. Moreover, regelation is also observed in relatively acidic solution (pH < 2), because the excess acid acts as a salt under these conditions and so induces a sphere-to-worm transition.
Cationic diblock copolymer worms can be used as flocculants for micrometer-sized silica particles provided that they are covalently stabilized via core cross-linking.
A range of cationic diblock copolymer nanoparticles are synthesised via polymerisation-induced selfassembly (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] PGMA x + [n] PQDMA y ) − PHPMA z 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 1 H 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 freestanding 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. † Electronic supplementary information (ESI) available: Aqueous gel permeation chromatograms of PQDMA macro-CTAs, TEM images of PQDMA-PHPMA spheres, DMF gel permeation chromatograms of PGMA-PHPMA di-block copolymers, TEM images of cationic worms, critical gelation concentration determination of cationic worms and rheology studies of cationic and non-ionic worms. See
Morpholine-functionalised poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) diblock copolymer vesicles are transformed into worms or spheres on lowering the solution pH.
Poly(ethylene imine) (PEI) has been adsorbed onto the surface of fumed silica particles at pH 10 in order to produce an effective "hybrid" Pickering emulsifier. Systematically increasing the PEI/silica mass ratio at a fixed silica concentration of 1.0% w/w modifies the silica particle surface and hence allows the formation of oil-in-water (o/w) Pickering emulsions prepared via homogenization of an aldehyde-rich multi-component fragrance oil (at 12,000 rpm for 2 min at 20 °C). Further increasing the PEI/silica mass ratio leads to phase inversion, producing water-in-oil (w/o) Pickering emulsions. Thus this approach allows formation of stable water-in-oil-in-water (w/o/w) double emulsions using two batches of hydrophilic and hydrophobic PEI/silica hybrid particles that differ only in their PEI/silica mass ratios prior to homogenization. Stable w/o/w double emulsions can be prepared with oil volume fractions ranging from 5 to 42%. Moreover, controlling the volume fraction of the w/o Pickering emulsion homogenized in the presence of an aqueous dispersion of the hydrophilic PEI/silica particles allows the mean diameter of the resulting oil droplets to be conveniently controlled between 20 and 160 μm. Fluorescence microscopy studies confirm that controlling the mean diameter of these oil droplets allows encapsulation of either single or multiple droplets within them. Although these double emulsions do not require cross-linking at either interface to withstand an alcohol challenge, epoxy-amine cross-linking between the physically-adsorbed PEI chains and either an oil-soluble or a water-soluble bisepoxy-based polymeric cross-linker can be achieved to produce novel colloidosomes-in-colloidosomes, which may offer payload retention benefits over conventional colloidosomes.
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