The assembly of particles is one of the many methods for the fabrication of organized structures in the range of nanometer sizes, with a view to material science applications of which many are being explored: photonic band-gap materials, electro-rheological fluids.
Colloidal suspensions are composed of particles in a solvent, where particle and solvent have different dielectric constants. In electric fields, chain-like structures form that result from a one-dimensional close packing along the electric field direction. Chain formation is followed by a coarsening of the chains into sheets. Eventually, the sheets transform into a three-dimensional crystal structure.
The colloid systems are study in a sinusoidal alternating field as a function of electrical strength and frequencies; at high-frequencies, where particles see an average field and low-frequency where electrohydrodynamic phenomena can be observed.
We present findings on the phase transitions of functionalized porous nanoparticles in a non-aqueous solvent under an applied electric field. The colloidal systems studied are dispersions of spherical particles in PDMS or methylcyclohexanol solvents, consisting of a porous silica core, partially filled with water molecules and coated with methacryloxypropyltriethoxysilane as stabilizing layer. The softness of the interaction is tuned in this colloidal suspension by varying the silica water content.
We report a real-time, Small Angles Neutrons Scattering and dynamic rheological measurements study of the evolution of structure in the system during the particles ordering. Experiments have been performed at different water content. Water influences the multi-scale ordering response in two different ways. At low water concentrations, it enhances the response by enhancing the interfacial polarization of the particle. While at large concentrations, the response degrades due to the non-linear conductivity in the continuous phase.
jacques.persello@unice.fr
