8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P3.36Fri 911:10-14:00Effect of polydispersity and soft interactions on thenematic versus smectic phase stability in plateletssuspensionsEnrique Velasco 1 and Yuri Martinez-Raton 21 Universidad Autonoma de Madrid, Avenida Tomas y Valiente s/n, Facultad de Ciencias28049, Madrid, Spain2 Universidad Carlos III de Madrid, Madrid, SpainPolydispersity is crucial to understand phase behaviour in experiments on colloidal suspensionsof particles with rod- or plate-like shape. Non-spherical colloidal particles are known to formliquid-crystalline phases, such as nematic, smectic and columnar, but the nematic phase is difficultto obtain experimentally in charge-stabilised platelike particles before the formation of smectic,columnar or gel phases. The effects of polydispersity and soft interactions are important as regardsthe stabilisation of the nematic phase. Here we discuss theoretically the phase stability ofnematic and smectic ordering in a suspension of platelets of the same thickness but with a highpolydispersity in diameter, and study the influence of polydispersity. We assume platelets to behard objects, but additional soft attractive and repulsive interactions are also considered. Our focusis on the nematic vs. smectic phase interplay, since a high degree of polydispersity in diametersuppresses the formation of the columnar phase due to incommensuration with a single lattice parameterof the triangular lattice formed by the columns. When interactions are purely hard, thetheory predicts a continuous nematic-to-smectic transition, regardless of the degree of diameterpolydispersity. However, polydispersity enhances the stability of the smectic against the nematicphase. In the case of one-component soft platelets, the transition remains continuous for repulsiveforces, and the smectic phase becomes more stable as the range of the interaction is decreased.The opposite behaviour with respect to the range is observed for attractive forces, and in fact thetransition becomes of first order below a tricritical point. Also, for attractive interactions, nematicdemixing appears, with an associated critical point. When platelet polydispersity is introduced thetricritical temperature shifts to very high values.36