A Smectic A Liquid Single Crystal Elastomer (LSCE): Phase Behavior and Mechanical Anisotropy

Abstract

The analysis of the phase behavior of a smectic A (SA) elastomer reveals a nematic phase existing within a small temperature range below the isotropic state. Stress‐optical measurements in the pretransformational regime of the isotropic state indicate smectic as well as nematic fluctuations yielding a critical exponent of γ = 0.65. The formation of the liquid single crystal elastomer (LSCE) at the isotropic to liquid crystalline phase transformation equals a nematic LSCE. At the nematic to SA phase transformation, the orientation of the director remains constant while the tendency of the network strands towards an oblate equilibrium conformation is suppressed by the high modulus parallel to the smectic layer normal. The mechanical anisotropy of the SA‐LSCE as a function of the temperature is characterized by entropy elasticity perpendicular to the smectic layer normal. Parallel to the layer normal the mechanical response is determined by the enthalpy elastic response of the smectic layers having a modulus larger by about two orders of magnitude. In this direction the modulus decreases linearly with increasing temperature and reflects the falling stability of the layers. Accordingly, above a deformation of about 2% the homogeneous layered structure breaks down at a threshold stress that also falls linearly with increasing temperature while the threshold strain remains constant at about 2% elongation.

Random disorder and the smectic-nematic transition in liquid-crystalline elastomers

“…The sample length passes a maximum, decreases slightly on approaching the nematic-smectic phase transformation, and remains constant in the smectic-A state. These results at low cross-link density are similar to those reported by Assfalg et al [35] and serve as a reference for the different behavior of the samples with 10% cross-links (see below). The SmA-N transition temperature T NA can be determined more precisely from an x-ray line-shape analysis, illustrated in Fig.…”

Shape‐Memory Effect Controlled by the Crosslinking Topology in Uniaxially‐Deformed Smectic C*Elastomers

“…[9][10][11][12][13] There have been a few investigations on the reversible shape change of nematic elastomers; however, much less work has been carried out on that of smectic elastomers, in spite of their potentially useful mechanical properties, owing to their one-dimensional crystalline structure. [14][15][16][17][18][19][20][21][22] In 1997, Nishikawa et al [14] succeeded in preparing a smectic A single-crystal elastomer (SmA-LSCE) and reported that the elastic constant in the direction parallel to the layer normal was about two orders of magnitude larger than the elastic modulus in the direction parallel to the layer, becauseoftheone-dimensionalcrystalline structure and the two-dimensional liquid-like fluidity of the elastomer.…”

Thermal and mechanical properties of new Main-Chain Liquid-Crystalline Elastomers

“…For smectic samples, the elasticity of the systems is inversely proportional to their crosslinking density, where the enthalpy elasticity factor from the smectic layers plays an important role [19][20][21]. This can be explained by the FIGURE 4 Uniaxial stress-strain curves for the samples SmC-MCE-10 and SmC-MCE-2.5 at T red ¼ 0.92 (smectic-C phase).…”