Thermal blooming measurement of specific heat and thermal conductivity in isotropicp-methoxy benzylidenep-butylanyline (MBBA) near clearing

Abstract

Using the thermal-lens effect, the specific heat $C_p$ and the thermal conductivity $\Lambda$ have been measured simultaneously in the isotropic phase of the liquid crystal MBBA ($p$-methoxy benzylidene $p$-butylanyline) near its isotropic-to-nematic transition. Accurate analysis of the lens dynamical behavior yields both transport coefficients provided the change of the refractive index with temperature, $\frac{\mathrm{dn}}{\mathrm{dT}}$, is known. A precise measurement of $n\left(T\right)\mathrm{}$ was carried out separately. The best fits yield the critical exponents 0.52 and 0.65 for $C_p$ and $\Lambda$, respectively, with a critical temperature $T_c$ equal to $T_p-0.21\mathrm{}\pm 0.01$°C, where $T_p$ is the clearing temperature. The present measurements give the first conclusive results on the critical behavior of $C_p$ in the isotropic phase of a liquid crystal.