The Interfacial Free Energy of Nematogen Droplets in an Isotropic Matrix: Determination of its Temperature Dependence from Coalescence Kinetics

Abstract

We have determined the surface free energy, [sgrave], at the interface between a nematogen and an isotropic liquid by measurement of the time constant for coalescence of nematogen droplets imbedded in the matrix. The basis for this technique is an analysis developed by Frenkel in 1945. The major conclusions of the present work are four-fold: 1) the magnitude of the interfacial free energy is on the order of 10–² to 10–¹ dyne/cm; 2) the temperature dependence of [sgrave] for nematic droplets shows a greater negative slope than for isotropic droplets; 3) the accuracy of the method is insufficient to detect a discontinuity in [sgrave] at the nematic to isotropic transition temperature; and 4) the interfacial free energy decreases toward zero as the temperature increases toward that at which the droplets dissolve in the matrix. This last behavior was expected by analogy with the Eotvos expression for ordinary liquid/vapor surface free energies. The droplet coalescence technique shows promise as a means for determining temperature-dependent interfacial free energies for other liquid/liquid systems.