Diffusion, aggregation and electrokinetics

This chapter touches on three fundamental concepts of physical chemistry, in general and of nanostructured fluids, in particular, that is diffusion, aggregation and electrokinetics. We will start from a very classical background on diffusion, introduced from a thermodynamic and a statistical point of view. We will then introduce the reader to the relevance of diffusion coefficients within the realm of nanoscience and nanotechnology. The diffusion coefficients provide access to central, structural and dynamical properties of nanostructured systems, that is their size and how they move in a medium, thus impacting also the permeability. Subsequently, the correlation between the Brownian motion and the chemical kinetics is discussed with emphasis on the coagulation kinetics, colloidal stability and the fractal dimension of the aggregates. The chapter ends with a section on electrokinetic effects where the phenomena of streaming potential, electroosmosis and electrophoresis are discussed using the models appropriate to understand the principle of functioning of the modern instrumentation used to evaluate the zeta-potential of particles and macroscopic surfaces.