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Osmotic equilibrium of colloids

Daniel Ou Yang, Lehigh University (USA)

par Salmon Jean-Baptiste - publié le , mis à jour le

To start, I will give an introduction and a brief overview of the research at the Emulsion Polymers
Institute at Lehigh University. This will include a collaboration we are establishing with Solvay Shanghai
on Pickering emulsions.

For the remaining portion of the talk, I will share a research in my lab on osmotic equilibrium of
colloids. The concept starts with Jean Perrin’s sedimentation equilibrium experiments where Perrin
used Einstein’s osmotic equilibrium equation to analyze the density profile of emulsion particles under
gravity. We further extend the osmotic equilibrium concept to analyze the colloidal particle density
profiles created by conservative force fields, such as the optophoresis force by a tightly focused laser
beam or the dielectrophoresis force by high frequency electric fields. We first quantify the spatial
distributions of the conservative force fields from the Boltzmann distribution of the density profile
distributions obtained by confocal imaging at very low particle densities where particle interactions
are negligible. We then use the force field and the particle density profiles at high particle densities to
determine the colloidal osmotic pressure as a function of the particle number density and temperature,
P(N,T). From the experimental P(N, T), one can then determine the chemical potential or free energy
in order to better connect with theory or simulations to predict phase transitions. For industrial
applications, this could be used as method for accurate determination of colloidal stability for colloids at
high concentrations.

Biographical sketch :

H. Daniel Ou-Yang is a Professor of Physics and Bioengineering and Director of the Emulsion Polymers
Institute of Lehigh University. He received B.S. and M.S. in Physics from Fu-Jen Catholic University
in Taiwan and Ph.D. in Physics from UCLA. He was a postdoctoral fellow at the Physics Department,
University of Pennsylvania, and at the Exxon Corporate Research Laboratory in New Jersey. Currently,
his research interests include colloids, soft matter and biological physics.