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Prof. Henk N. W. Lekkerkerker

Van't Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute, Utrecht University, The Netherlands

Friday, October 28th, 2011 at 11:00:00 AM

Conference room Querzoli - LENS - via Nello Carrara 1 - Sesto Fiorentino (Florence)

Published on-line at 12:24:30 PM on Wednesday, October 26th, 2011

Phases and interfaces in colloidal suspensions

Ordering in systems with purely repulsive inter-particle forces: suspensions of colloidal particles are the main characters of next Enrico Fermi Colloquium.

Suspensions of colloidal particles display rich phase behaviour. Depending on shape and interactions, colloidal gas, colloidal liquid, colloid crystal and colloidal liquid crystal phases are observed.

The fact that such ordering can occur in suspensions in which inter-particle forces are purely repulsive provides a dramatic realisation of the predictions made by Lars Onsager in the 1940's. He showed that a balance of entropic terms drives the ordering transition; the entropy of confinement favouring randomness versus the entropy of excluded volume favouring ordering. Due to the fact that the colloidal length scale is typically 1000 times larger than for atoms the interfacial tension is much lower than in atomic and molecular systems (down to nN/m instead of mN/m). This ultra low interfacial tension has pronounced effects on the kinetics of phase separation and the wetting profile near a wall.

In this talk I will present experimental results for the entropy driven phase transitions and the interface of demixed colloid-polymer mixtures and the isotropic-nematic interface in suspensions of colloidal platelets, showing the effect of ultralow interfacial tension.

Klein Colloquium by Gabriele Rosi: Misura della costante gravitazionale con interferometria atomica.