Polymerization-induced self-assembly (PISA) was employed to compare the self-assembly of different amphiphilic block copolymers. They were obtained by emulsion polymerization of styrene in water using hydrophilic poly(N-acryloylmorpholine) (PNAM)-based macromolecular RAFT agents with different structures. An average of three poly (ethylene glycol acrylate) (PEGA) units were introduced either at the beginning, statistically, or at the end of a PNAM backbone, resulting in formation of nanometric vesicles and spheres from the two former macroRAFT architectures, and large vesicles from the latter. Compared to the spheres obtained with a pure PNAM macroRAFT agent, composite macroRAFT architectures promoted a dramatic morphological change. The change was induced by the presence of PEGA hydrophilic side-chains close to the hydrophobic polystyrene segment.

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Physical hydrogels of chitosan in the colloidal domain were obtained in the absence of both cross-linker and toxic organic solvent. The approach was based on a reverse emulsion of a chitosan solution in a Miglyol/Span 80 mixture, generally regarded as safe. Temperature and surfactant concentration were optimized, and the impact of the degree of acetylation (DA) and the molar mass of chitosan was investigated. When chitosan had a DA above 30%, only macroscopic gels were obtained, because of the predominance of attractive Van der Waals forces. The lower the molar mass of chitosan, the better the control over particle size and size distribution, probably as a result of either a reduction in the viscosity of the internal aqueous phase or an increase in the disentanglement of the polymer chain during the process. After extraction and redispersion of the colloid in an ammonium acetate buffer, the composition of the particles was around 80% of pure chitosan corresponding to a recovery of 60% of the original input. These new and safe colloids offer wide perspectives of development in further applications.

Colloidal physical gels of pure chitosan were obtained via an ammonia-induced gelation in a reverse phase emulsion. The water weight fraction and the chitosan concentration in the water phase were optimized so as to yield nanogels with controlled particle size and size distribution. The spherical morphology of the nanogels was established by transmission electron microscopy with negative staining. Wide-angle X-ray scattering experiments showed that these gels were partially crystalline. The electrophoretic mobilities of the particles remained positive up to pH 7, above which the particles aggregated due to the charge neutralization. From the investigation on the colloidal stability of these nanogels in various conditions (pH, salt concentration, temperature), an electrosteric stabilization process of the particles was pointed out, related to the conformation of mobile chitosan chains at the gel-liquid interface. Therefore, the structure of the nanogels was deduced as being core-shell type, a gelified core of neutralized chitosan chains surrounded by partially protonated chains.

The relationship between interaction range, structure, fluid-gel transition, and viscoelastic properties of silica dispersions at intermediate volume fraction, Φv ≈ 0.1 and in alkaline conditions, pH = 9 was investigated. For this purpose, rheological, physicochemical, and structural (synchrotron-SAXS) analyses were combined. The range of interaction and the aggregation state of the dispersions were tuned by adding either divalent counterions (Ca(2+)) or polycounterions (PDDA). With increasing calcium chloride concentration, a progressive aggregation was observed which precludes a fluid-gel transition at above 75 mM of calcium chloride. In this case, the aggregation mechanism is driven by short-range ion-ion correlations. Upon addition of PDDA, a fluid-gel transition, at a much lower concentration, followed by a reentrant gel-fluid transition was observed. The gel formation with PDDA was induced by charge neutralization and longer range polymer bridging interactions. The refluidification at high PDDA concentrations was explained by the overcompensation of the charge of the silica particles and by the steric repulsions induced by the polycation chains. Rheological measurements on the so-obtained gels reveal broad yielding transition with two steps when the size of the silica particle clusters exceeds ≈0.5 μm.

Investigations of polymerization-induced self-assembly in emulsion were conducted using MD simulations. Using umbrella sampling and the Weighted Histogram Analysis Method (WHAM) algorithm, we calculated the interaction free energy between different self-assembled copolymer aggregates. In the presence of poly(ethylene glycol) (PEG) at 80 • C side chains an attractive interaction between the copolymer micelles is observed. This attractive well is followed, in some case, by a repulsive barrier depending on the position of the PEG side-chains. The strength of this repulsive barrier controls the aggregation kinetics: a strong repulsive barrier leads to slower aggregation rate and thus larger and denser clusters (i.e. reaction limited cluster aggregation).Theses clusters then coalesce into large vesicles due to the presence of interstitial water molecules in the cluster. Inversely, a weak repulsive barrier causes a rapid aggregation which gives loose and ramified clusters (i.e. diffusion limited cluster aggregation) that coalesce after swelling with hydrophobic monomer, leading to tubular nano-structures and small vesicles. This new mechanism approach can explain the change of morphology from spheres to fibers and vesicles depending on the polymer architecture in the case of polymerization-induced self-assembly (PISA) in emulsion. Umbrella Sampling E separation slow aggregation (RLCA) fast aggregation (DLCA) w ea k re pu ls iv e ba rr ie r st ro ng re pu ls iv e ba rr ie r Swelling Coalescence Large vesicles Fibers Small vesicles interstitial water Self-assembled block copolymers micelles Swelling Coalescence

Polymerization-induced self-assembly (PISA) was employed to compare the self-assembly of different amphiphilic blockc opolymers.T hey were obtained by emulsion polymerization of styrene in water using hydrophilic poly(Nacryloylmorpholine) (PNAM)-based macromolecular RAFT agents with different structures.A na verage of three poly (ethylene glycol acrylate) (PEGA) units were introduced either at the beginning,s tatistically,o ra tt he end of aP NAM backbone,r esulting in formation of nanometric vesicles and spheres from the two former macroRAFT architectures,a nd large vesicles from the latter.Compared to the spheres obtained with ap ure PNAM macroRAFT agent, composite macro-RAFT architectures promoted ad ramatic morphological change.T he change was induced by the presence of PEGA hydrophilic side-chains close to the hydrophobic polystyrene segment.