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

P3.10Fri 911:10-14:00Isotropic to nematic phase transition in mixtures withdouble peak specific heat anomalyDalija Jesenek, 1 Samo Kralj, 1 Vlad Popa-Nita, 2 George Cordoyiannis, 1 andZdravko Kutnjak 11 Jozef Stefan Institute, Jamova 39, 1000, Ljubljana, Slovenia2 Faculty of Physics, University of Bucharest, Bucharest, RomaniaIn the recent years, many investigations on mixtures composed of liquid crystals and nano- ormicro-size particles, such as colloids and silica aerosils, have been preformed [1-3]. In thesecomposite systems a double-peak critical anomaly has been often observed in the temperaturedependence of the heat capacity, Cp [3-5]. In our contribution we have analysed two possibleorigins for this anomaly: i) phase separation and ii) surface wetting or dewetting transition. Inorder to theoretically predict the conditions for which the observed phenomena can appear, wehave used the Landau-de Gennes approach. In the phase separation model this approach has beencombined with the Flory-Huggins one. First, the phase separation has been considered. Thephase behaviour has been studied across the isotropic-nematic (I-N) phase regime on varying thesurface interactions. It is demonstrated that few possible phase diagrams can exist for which thesystem exhibits a double-peak I-N phase transition in a finite interval of concentrations. Next wehave focused on wetting and dewetting phenomena at the isotropic-nematic (I-N) phase transition.We consider linear and square order parameter in the surface potential, separately. It has beenshown that in an appropriate interval of anchoring strengths, on lowering the temperature, eitherfirst order prewetting or dewetting surface transition can be the reason for the observed doubleanomaly at the liquid crystal-particle interface.[1] V. J. Anderson, E. M. Terentjev, S. P. Meeker, J. Crain, W. C. K Poon, Eur. Phys J. E4, 11 (2001).[2] G. Cordoyiannis, G. Nounesis, V. Bobnar, S. Kralj, Z. Kutnjak, Phys. Rev. Lett. 94, 027801(2005).[3] J. Yamamoto and H. Tanaka, Nature 409, 321-325 (2001).[4] A. Roshi, G. S. Iannacchione, P. S. Clegg and R. J. Birgeneau, Phys. Rev. E 69, 031703(2004).[5] F. Mercuri, S. Paolini, U. Zammit and M. Marinelli, Phys. Rev. Lett. 94, 247801 (2005).10