Critical linear thermal expansion in the smectic-Aphase near the nematic-smectic phase transition

Abstract

Recent high-resolution x-ray investigations of the smectic- A (SmA) phase near the nematic-to-SmA transition provide information about the critical behavior of the linear thermal expansion coefficient alpha// parallel to the director. Combining such data with available volume thermal expansion alpha(V) data yields the in-plane linear expansion coefficient alpha(perpendicular) . The critical behaviors of alpha// and alpha(perpendicular) are the same as those for alpha(V) and the heat capacity Cp. However, for any given liquid crystal, alpha//(crit) and alpha(perpendicular)(crit) differ in sign. Furthermore, the quantity alpha// (crit) is positive for SmAd partial bilayer smectics, while it is negative for nonpolar SmAm monomeric smectics. This feature is discussed in terms of the molecular structural aspects of these smectic phases.

High-resolution x-ray study of nematic–smectic-Aand smectic-A–reentrant-nematic transitions in liquid-crystal–aerosil gels

“…The linear thermal expansion coefficient || α = (1/d)(∂d/∂T) is positive in the N phase and in the SmA phase just below T 1 * for both global and free fits. Indeed, || α exhibits a peak at T 1 *, as expected from detailed studies of the critical linear thermal expansion observed near N-SmA transitions [20]. However, the behavior of || α near T 2 *…”

“…See Ref. 20 for further details of critical linear thermal expansion at nematic -smectic-A transitions. Since the SmA phase is weakly ordered in reentrant LC+aerosil samples, this suggests that the aerosil destabilizes the nematic phases more than it does the SmA phase in order to account for this stabilization of the SmA phase at slightly higher concentrations.…”

“…See Ref. 20 for further details of critical linear thermal expansion at nematic -smectic-A transitions.…”

Dimensional crossover and scaling behavior of a smectic liquid crystal confined to controlled-pore glass matrices

“…This is in accordance with all previous reports concerning the layer spacing evolution in the SmA phase of longer-chain alkylcyanobiphenyls. 27,32,33 For all pore sizes from 291.7 nm down to 15.1 nm a rather constant dilation of the smectic layers is observed. Nevertheless, a noteworthy feature occurs for the smallest pore radii.…”

Phase behaviour of novel liquid crystalline mixtures based on thiobenzoates†

“…Phase diagrams for these systems were found to have the following features: a line of continuous SmA-SmC transitions, a line of second order N-SmA transitions, a line of first order N-SmC transitions, and a multicritical point where these three lines meet. Critical and tricritical behaviour at the nematic to smectic A transition in the nOS5 homologous series were studied before [18][19][20][21]. The fact that the N-SmC line branches at the policritical point into the N-SmA and SmA-SmC lines, which are lines of continuous transitions, suggests that this point has tricritical characteristic.…”