Interplay between slow interfacial water diffusion and colloid dynamics: A way to probe colloidal transitions.

Abstract

ABSTRACTParticle fluctuations in colloidal suspensions are generally considered to be much slower than the embedded fluid dynamics. It was recently proposed that the fluid self-diffusion nearby an interface follows Lévy statistics, extending the time domain of the fluid dynamics towards the low frequency range. It is then possible to probe colloidal particle motion and especially its evolution during a phase transition looking at the slow dynamics of the fluid molecule close to an particle surface. Using field cycling NMR relaxometry, we show how the slow and confined water dynamics at proximity of a colloidal surface provide an original way to follow the glass transition of a colloidal system made of plate-like Laponite particles, a synthetic clay. The interplay between fluid Levy dynamics and particle jamming is discussed. An analytical model involving correlated elementary water time steps on the colloidal interface is proposed and critically compared to our experimental data. The method permits probing of colloidal motions and especially their evolution during a phase transition in a new way. This method can be extended to other systems including mineral lyotropic liquid crystals and biological molecular structures.