Crystallization Tendencies of Glass-Forming Liquids: High Pressure Versus Nanoscale Confinement

High pressure and nanometer scale confinement are very popular strategies used to tune the crystallization tendencies of various systems. At first sight, they both seems to be entirely different, non-connected realm governed by their own rules. However, the effects generated in both environments are not so much distinct. Experimental studies, as well as molecular simulations, have proven that certain structural transformations and chemical reactions that occur only at high pressures in the bulk phase also appear under spatial confinement. High pressure and confinement at nanoscale level affect the molecular packing and intermolecular interactions, which have a dramatic influence on the key parameters governing the overall crystallization outcome. In result, it is possible to change the crystallization behavior of a given substance or obtain materials with interesting physicochemical properties, sometimes not attainable by other means. However, mentioned above changes might not be necessarily identical in both environments. Here, we have investigated changes in the crystallization rate for molecular liquids studied on increased pressure and confined to pores of the nanometer scale. Variations in the crystallization rate were studied by varying with pressure and the size of the spatial constraints. We show that avoiding crystallization when cooling liquid from the melt becomes more challenging with increasing pressure. This is because compression increases the rate of crystallization, broadens the overall crystallization rate curve and shifts its maximum with respect to Tm-T. On the other hand, when decreasing the size of the confining space a completely opposite trend is observed. To rationalize these changes in the crystallization behavior of the glass-forming liquids predictions of the classical theories of nucleation and crystal growth we employed. Following our recent idea of investigating crystallization of the supercooled liquids along various iso-invariant curves (Cryst. Growth Des.2016), we also show how they evolve in both environments.