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 an...

High-resolution ac calorimetry has been used to study the nematic to smectic- A (N-SmA) phase transition in the liquid crystal octylcyanobiphenyl (8CB) confined in aligned colloidal aerosil gels. A stable and robust nematic alignment was achieved by repeated thermal cycling of the samples in the presence of a strong uniform magnetic field. In some ways (such as transition temperature and integr...

We report on a comparison between the random disorder effects of an hydrophobic (R812) or an hydrophilic (A380) aerosil on the order and dynamics of the 3βDOXYL-5α-cholestane spin probe in the liquid crystal 4-n-pentyl-4’-cyanobiphenyl (5CB) using the ESR technique. Increasing the aerosil concentration up to 3 wt % the probe order parameter is depressed with a larger effect for the hydrophilic ...

This study explores the role of aerosil dispersion on activated phase transitions of bulk octylcyanobiphenyl (8CB) liquid crystals by performing heating rate-dependent experiments. Differential scanning calorimetry (DSC) was used at various heating ramp rates in order to probe the activated phase dynamics of the system. The system, LC1-xSilx, was prepared by mixing aerosil nanoparticles (7 nm i...

A high-resolution calorimetric spectroscopy study has been performed on pure glycerol and colloidal dispersions of an aerosil gel in glycerol covering a wide range of temperatures from 300 to 380 K, deep in the liquid phase of glycerol. The colloidal glycerol+aerosil samples with 0.07, 0.14, and 0.32 g of silica per cm3 of glycerol reveal activated energy (thermal) dynamics at temperatures well...

We have studied a system composed of an hydrophobic aerosil (R812) dispersed in the liquid crystal 4-n-octyl-4’-cyanobiphenyl (8CB) using the spin probe ESR technique and, in particular, we have determined, for different aerosil concentrations, the temperature dependence of the orientational order parameter 〈P2〉 and the rotational diffusion coefficient D⊥ of the probe 5-doxyl stearic acid in th...

High-resolution x-ray scattering studies of the nonpolar thermotropic liquid crystal 4-n-pentylphenylthiol-4'-n-octyloxybenzoate (8S5) in aerosil gel nanonetworks reveal that the aerosil-induced disorder significantly alters both the nematic to smectic-A and smectic-A to smectic-C phase transitions. The limiting 8S5 smectic-A correlation length follows a power-law dependence on the aerosil dens...

There is a well-known de Gennes coupling between the scalar nematic order parameter S and the smectic density-wave amplitude /Psi/, which causes the nematic-smectic-A phase transition to cross over from second order to first order via a tricritical point. This sort of crossover is observed for numerous liquid crystals (LCs) with small to moderate nematic ranges. Recent studies of LC+aerosil sys...

We have studied the effects of quenched random disorder created by dispersed aerosil nanoparticle gels on the nematic to smectic- A (N- SmA ) and smectic- A to reentrant nematic ( SmA -RN) phase transitions of thermotropic liquid-crystal mixtures of hexyloxycyanobiphenyl (6OCB) and octyloxycyanobiphenyl (8OCB). These effects are probed using high-resolution synchrotron x-ray diffraction techniq...

High-resolution x-ray diffraction and ac-calorimetric experiments have been carried out on the liquid-crystal octyloxycyanobiphenyl in which aerosil particles are dispersed. The measurements were made over a temperature range around the bulk nematic to smectic-A transition temperature. At this transition the liquid crystal breaks translational symmetry in a single direction. The silica particle...