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Abstract
We report on calorimetric measurements carried out in an upgraded Photopyroelectric set up enabling a frequency dependence detection of the specific heat and of the latent heat exchanged over first order transitions as well as the simultaneously determined optical turbidity obtained from light scattering measurements. It has been applied to the Nematic-Isotropic transition of 8CB liquid crystal confined in a silica nanoparticle network, where the specific heat shows a double peak structure. The larger strain involved with the nematic phase nucleating over the low temperature peak, due to the interaction of the liquid crystal molecules with the network, induces a considerable lower latent heat than the one involved with the quasi bulk like nematic material nucleating over the higher temperature peak. Moreover, the frequency dependent measurements have shown a substantially different dynamics of the nematic nucleating over each of the peaks. The determined nematic correlation length, obtained from turbidity measurements, showed the characteristic two step-like nematic nucleation process previously reported only for the specific heat.
The authors from NRDIIMT Cluj-Napoca, Romania, acknowledge financial support by the Italian Ministry of Foreign Affairs, Directorate-General for Cultural Promotion and Cooperation, and Romanian National Authority for Scientific Research, Ministry of Education and Research, through Project no. 12/2006 for mobility exchange under the 15th Italian-Romanian Executive Programme of S&T Cooperation, 2006–2008.