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Osmotic equilibrium for colloidal suspensions in a potential force field

H. Daniel Ou-Yang, Lehigh University (USA)

17 juin 2016

Colloidal particles in suspension reach an equilibrium density distribution under external potential forces, such as gravity. In the absence of particle interactions the density distribution is known to follow a Boltzmann distribution of the potential energy profile. In the presence of particle interactions, however, the particle number density profile depends on the details of the colloidal interactions between the particles. According to the equation developed by Einstein for the osmotic equilibrium of a colloidal suspension under a potential force, the colloidal equation of state can be determined from the density distribution if the potential force profile is known. This seminar will begin with an introduction of Einstein’s theory of osmotic equilibrium, a brief history of Perrin’s experiment, and then demonstrations on how one could use the their ideas and take advantage of the advanced optical imaging techniques to determine colloidal osmotic equation of state by external potential forces produced by electromagnetic fields to determine the colloidal equation of state as well as to predict phase transitions when the colloidal interactions are varied by changing ionic screening or by polymer-induced depletion attraction. Possibilities of extending Einstein’s original idea for equilibrium systems to non-equilibrium systems such as a suspension of active particles