Evolution of the isotropic-to-nematic phase transition in octyloxycyanobiphenyl+aerosil dispersions

Abstract

High-resolution ac-calorimetry has been carried out on dispersions of aerosils in the liquid crystal octyloxycyanobiphenyl (8OCB) as a function of aerosil concentration and temperature spanning the crystal to isotropic phases. The liquid-crystal 8OCB is elastically stiffer than the previously well studied octylcyanobiphenyl (8CB)+aerosil system and so, general quenched random disorder effects and liquid-crystal specific effects can be distinguished. A double heat capacity feature is observed at the isotropic to nematic phase transition with an aerosil independent overlap of the heat capacity wings far from the transition and having a non-monotonic variation of the transition temperature. A crossover between low and high aerosil density behavior is observed for 8OCB+aerosil. These features are generally consistent with those on the 8CB+aerosil system. Differences between these two systems in the magnitude of the transition temperature shifts, heat capacity suppression, and crossover aerosil density between the two regimes of behavior indicate a liquid crystal specific effect. The low aerosil density regime is apparently more orientationally disordered than the high aerosil density regime, which is more translationally disordered. An interpretation of these results based on a temperature dependent disorder strength is discussed.Finally, a detailed thermal hysteresis study has found that crystallization of a well homogenized sample perturbs and increases the disorder for low aerosil density samples but does not influence high density samples.

Dynamics at the Nematic-Isotropic Phase Transition in Aerosil Dispersed Liquid Crystal

“…It should be noted, moreover, that the crossover from RD to RF does not depend on the aerosil concentration only, but it is also material dependent. It has been shown, in fact, that if the LC becomes stiffer, then the crossover takes place at a larger concentration [12]. This is, of course, a general conclusion and does not apply to LC only.…”

Thin films of silica nanoparticle doped nematic liquid crystal 7CB for electro-optic modulation

“…Actually, the SiNPs dopants lead to formation of a gel network in the SiNPs-7CB [10]. Namely, the random flexible network gives rise to disorders of the LC phase and finite size effects [8,[11][12][13]. Because of the presence of the network, domains are formed with random distribution of director orientation of each domain, and the normal structure as well as phase transitions of the partly orientationally ordered mesophases are disturbed.…”

Slow molecular processes in a nematic liquid crystal confined to random porous network formed by aerosil particles

“…Their composite nature profoundly affects the ordering of the LC molecules and their susceptibility to external fields, making them ideal for electro-optic applications [1]. Among the confined LC systems, LC-aerosil dispersions are demonstrated to be particularly interesting to study through many distinct experimental and theoretical methodologies [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. While porous matrices like nucleopore, anopore, millipore, and controlled porous glass (CPG) all have a well-defined geometry of the pores, aerosil, and *Corresponding author.…”