Interfacial and Intermittent Dynamics of Water in Colloidal Systems as Probed by Fast Field-cycling Relaxometry
This chapter presents several experimental examples in which the water dynamics close to a colloidal interface can be probed by nuclear magnetic relaxation dispersion (NMRD). Three classes of systems are presented: a porous plaster exhibiting large flat surfaces, a colloidal gel of finite clay particles and a suspension of very long and rigid nanorods. For these three colloidal systems, the spin–lattice relaxation is driven by intra-dipolar or quadrupolar magnetic interactions. At low magnetic field, the relaxation is essentially sensitive to the rotational dynamics of the water molecule and the time evolution of the surface director probed by the molecule during its self-diffusion. To model these experiments, we propose an analytical model of the intermittent dynamics of water involving successive excursions in the confined bulk and relocation/adsorption on the colloidal surface. This analytical approach is uniquely based on the use of temporal first-passage statistics. For water, we show how NMRD experiments provide an original characterization of the surface nano-wettability, being also sensitive to the particle geometry.