Reversible Nucleation, Growth and Dissolution of Poly(γ-benzyl L-glutamate) Hexagonal Columnar Liquid Crystals by Addition and Removal of a Nonsolvent

We have investigated the process of nucleation and growth and its reversal, i.e. dissolution, of ordered poly(γ-benzyl-L-glutamate) (PBLG) objects in thin film solutions containing a few percent of α-helical PBLG dissolved in chloroform. Nucleation, growth and dissolution rate were controlled by adding and removing, respectively, defined amounts of a nonsolvent (methanol), introduced through the vapor phase by regulating its flow rate and vapor pressure. Adding methanol to the isotropic polymer solution allowed to induce nucleation and growth even polymer solutions of very low concentrations, which were significantly below the solubility limit (equilibrium volume fraction). The variation of the number density of nuclei with the supersaturation ratio was found to fit well the predictions of the classical nucleation theory, for all equilibrium concentrations. For a given supersaturation ratio, fewer objects were nucleated for lower equilibrium concentrations.