Nonlinear Refractive Index and Thermal Diffusivity Measurements Near the Reentrant Isotropic – Discotic Nematic Phase Transition

Abstract

In this work we report on measurements, as a function of the temperature, of the nonlinear refractive indices parallel () and perpendicular () to the nematic director near the reentrant isotropic – discotic nematic phase transition in a lyotropic mixture of potassium laurate, decanol and D ₂ O. Thermal diffusivities, parallel ( D _∥) and perpendicular ( D _⊥) to the director in this reentrant isotropic–discotic nematic phase transition, were also obtained as a function of the temperature from Z-scan experiment and interpreted through a thermal lens model. The ratios and D ∥/ D _⊥ are less than one in this nematic phase. These results are discussed in terms of structural changes in the micellar configuration which takes place in each nematic phase transition.

Keywords:

• discotic nematic
• nonlinear refractive index
• thermal diffusivity

Acknowledgments

We are thankful to the Brazilian Agencies CAPES, CNPq and Fundação Araucária (PR) for the financial support of this work. Many thanks are due to T.A.Pedreira (Brazil) for the careful reading on the redaction of the manuscript.