Abstract

In the early 1950’s Noble Prize winner Paul J.Flory visited Nagoya University. During this visit two young researchers from the Physics Department of Nagoya University,Sho Asakura and Fumio Oosawa reported unpublished theoretical results on two bodies immersed in a solution of nonadsorbing polymer chains showing that an attractive interaction appears [1]. The very positive response of Flory resulted in submission of this work leading to a seminal paper with the first theoretical prediction of what is now known as the depletion force [2]. Starting in the late 1950s it was observed that the addition of non-adsorbing polymers to colloidal suspensions may lead to a phase separation in a colloid-rich and polymer-rich phase Such polymer induced phase separations are very important not only for colloid science but also in industrial and biological systems [3]. It has also been realised that procedures based on the depletion interaction have the potential to enable powerful and cost-effective fabrication approaches to materials based on self organized colloidal structures. In this talk I will discuss experiments performed in collaboration with Louise Bailey (Schlumberger Cambridge Research) and Geoff Maitland (Imperial College London) on mixed suspensions of mineral colloidal plates (Hectorite,Montmorillonite,Gibbsite) and small silica spheres. The small silica spheres act as depletion agents. On the one hand we observe liquid crystals at low colloid concentrations but also nonequilibrium states such as colloidal glasses and colloidal gels.Attempts to understand this complex equilibrium and non equilibrium phase behaviour will be presented .It appears that the development of the field is hampered more by conceptual locks than by factual locks

1 F.Oosawa .Hyo-Hyo Rakagu.Autobiography ,Nagoya,2005 2 S.Asakura and F.Oosawa,J.Chem.Phys.,22:1255(1954) 3For a historical overview on depletion effects and manifestations of depletion effects of biological and technological interest see H.N.W. Lekkerkerker and R Tuinier Depletion Interaction and Phase Behaviour in Colloidal Dispersions Springer To appear May 2011