Gerald R. Van Hecke Research
Thermodynamics and statistical thermodynamics of liquids, particularly liquid crystals. Preparation of new liquid crystalline materials. Light-scattering methods for determination of thermodynamic properties.
Compounds already reported in the literature are synthesized with the aim of using them for testing various physical models of liquid crystalline behavior. Most recently we have synthesized molecules that exhibit discotic liquid crystalline phases or reentrant phases. Transition metal containing liquid crystals are current a project.
Most recently we have looked at the volume-temperature behavior of a discotic material and found that the discotic phase we studied was less dense than the higher temperature isotropic phase it transforms into, that is dp/dT is negative rather the expected positive.
When crystals mix, often strange phenomena are observed. Our studies focus on the origin of such strange effects. Generally when two liquid crystalline materials with the same type of liquid phase mix under the appropriate conditions of temperature and pressure, a liquid phase with the same structure as the starting liquids results. For some liquid crystals, however, mixing two similarly structured liquids gives a liquid phase different in structure from the original and never observed in either of the pure materials. This new liquid phase is called an induced phase. One of our current projects is to understand the origin of this induced phase. We often approach such problems experimentally and theoretically. Experimental techniques generally involve the determination of various physical properties of the mixtures followed by thermodynamic analysis of the results. Theoretical approaches involve statistical thermodynamic calculations based on various models for intermolecular potentials, or purely thermodynamic approaches using what is called the equal Gibbs energy analysis.
Classic chelating ligands, such as ß-diketonates, when suitably modified with long aliphatic chains in appropriate positions, will not only chelate metals but the resulting compounds often exhibit liquid crystalling behavior. Since liquid crystals are orientable fluids, it is possible to orient a transition metal with respect to some known coordinate frame and study the metal’s electronic spectra with polarized photons.