Modelling phase equilibrium in nanoparticle-filled nematic liquid crystals

EZEQUIEL R. SOULÉ; LINDA REVEN; ALEJANDRO D. REY

Simposio; CSACS Students Symposium; 2010

Liquid Crystal (LC) nanocomposites have received much attention as new functional materials with interesting properties, due to the possible formation of different multi-scale structures, arising from the coupling between phase separation, texturing and defect formation of the LC matrix, and self-assembly of the nanoparticles1,2,3. Some major challenges in nanocomposite research involves creating the means to control the extent of dispersion of the nanopartciles (NPs) in the host matrix, and to control the characteristics of the structures formed. Knowledge of the basic thermodynamic aspects of phase separation, phase ordering and structure formation are of fundamental importance for this issue.The focus of this work is to analyze the fundamental aspects of phase separation and phaseordering, by means of a mean-field continuum thermodynamic model. This model takes into account mixing, nematic ordering of the LC, crystalline ordering (self-assembly) of the nanoparticles, and LC-NP interactions. The nematic and crystalline orderings are represented by two non-conserved order parameters, S and s, that measure the degree of order respectively. Four possible phases exist: Isotropic (S = s = 0), nematic (S>0, s=0) crystal (S=0, s>0), and nematic-crystal (S>0, s>0). Phase coexistence between the possible combinations of these four phases are calculated. Phase diagrams are found to depend significantly on different model parameters, like particle size and specific interaction parameters.