Julien Hernandez

Formation of rodlike silica aggregates directed by adsorbed thermoresponsive polymer chains.

This study deals with the fine-tuning of the interactions between silica nanoparticles and a LCST polymer in order to build permanent rigid linear aggregates. LCST polymers become hydrophobic and collapse above a critical temperature. The collapse of the polymer chains at the surface of the silica particles generates an attractive potential that can overcome the repulsive electrostatic forces between the silica particles under certain circumstances. The combined use of the thermoresponsiveness of poly(ethylene oxide) and of the chemical condensation properties of silica enables us to build permanent rigid aggregates displaying rodlike shapes just by increasing the temperature. These aggregates have been characterized using two complementary techniques: transmission electron microscopy and small angle neutron scattering. For low curing time, it appears that small linear aggregates are obtained when the electrostatic surface potential (pH = 8.5) is high and the initial ionic strength is low (I approximately = 10(-3) M). For higher heating time these objects aggregate further leading to some branching and ultimately to 3D gels which phase separate.