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  Chemistry, Catalysis, Polymers and Processes (UMR 5265)


Internship Multi-responsive hybrid microgels
October 05, 2020

Multi-responsive hybrid microgels by in situ polymerization

Research topics: colloids, radical polymerization, microgels, hybrid materials


Context: Microgels are crosslinked polymer particles swollen with a solvent. Soft and deformable, they have the ability to expand or contract reversibly in response to external stimuli such as pH, temperature, or light. Their responsive character makes them particular attractive for applications in biomedicine or cosmetics.

Microgel particles are generally obtained by precipitation polymerization. They are most often composed of thermoresponsive polymers that precipitate at high temperature during particle formation (their colloidal stability being ensured by the initiator fragments) and increase in volume (swell) when the medium is cooled (cf. scheme). Among the large variety of thermoresponsive polymers reported in the literature, those based on poly(ethylene glycol) methacrylate (PEGMA) are particularly interesting. These are made of a hydrocarbon main chain and poly(ethylene glycol) (PEG) side chains. The repeating oxyde units form hydrogen bonds with water conferring an hydrophilic character to the polymer while the hydrocarbon backbone gives it hydrophobic properties. Meth(acrylic) acid units can also be incorporated in the chains to introduce ionizable groups. It is thus possible to modulate their lower critical solubility temperature (LCST) by varying the pH, the composition, the number of ethylene oxide units and the chain length. To broaden the range of potential applications of microgels, it is essential to introduce functionalities. Significant attention has therefore been devoted in recent years to the incorporation of inorganic particles. However, very few studies have been conducted so far on hybrid microgels based on PEG.

During this research internship, we propose to synthesize multi-responsive hybrid microgels based on oligo (ethylene) glycol methacrylates and inorganic nanoparticles (e.g. silica and cerium oxide). In order to impart a pH-sensitive character to these microgels, we will also introduce a certain amount of methacrylic acid. We will focus on the influence of experimental conditions (pH, T, ionic strength, composition of the monomer mixture, nature and concentration of the inorganic particles) on the polymerization kinetics, the internal structure of microgels and their morphology. We will also study the influence of the inorganic particles on the swelling properties of the network and try to establish a link between the morphology of the particles and the swelling ratio. Finally, in a final part, we plan to mineralize the microgel particles by forming a silica shell at their surface. This internship will combine experiments in inorganic synthesis, chemistry and physico-chemistry of polymers as well as in the elaboration of materials. Salary corresponds to standard internship wages (ca. 560€/month).

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