Effect of confinement and strain on the specific heat and latent heat over the nematic-isotropic phase transition of 8CB liquid crystal.
Simultaneous measurements of the specific heat, latent heat, light scattering, and polarization microscopy were carried out in 8CB liquid crystal confined in Aerosil and Millipore membranes networks, to assess the different properties of the nematic material nucleating over the nematic-isotropic transition under different strain conditions. In Aerosil networks, it was found that the higher temperature peak of the double-peaked structure observed in the specific heat survived up to silica concentration values considerably larger than previously reported. Moreover, the first-order character of the transition occurring over the lower temperature peak, where the involved strain is larger, was considerably smaller than that observed over the larger temperature one as observed in the latent heat detection and hysteretic behavior. The dynamics of the nucleated nematic, characterized by the frequency dependence of the real and imaginary parts of specific heat and of the detected latent heat, was also shown to be markedly different over the lower temperature peak with respect to that observed over the higher temperature peak where it was similar to that of bulk material. Corresponding investigations carried in LC confined in Millipore membranes show that the nucleated nematic possesses characteristics similar to the ones observed over the higher temperature peak in Aerosils in terms of the dependence of the latent heat and of the specific heat from increasingly confining conditions and frequency, consistently with a less strain inducing environment with respect to Aerosils.
Dipartimento Ingegneria Meccanica, Universita di Roma Tor Vergata, Rome, Italy. zammit@uniroma2.it
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Marinelli
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Mercuri
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