Selection of a host material for gas storage and separations, ion transport and catalysis often requires consideration of tradeoffs between the inherent capabilities of porous solids and liquids. Porous solids offer high internal surface areas that enable the accommodation of a high density of guest species, while liquids offer intrinsic fluidity that enables chemical species to be efficiently delivered to where and when they are needed in continuous processes. Developing materials that feature both porosity and fluidity - two properties of matter that rarely coexist in conventional materials - would provide access to new capabilities for both porous solids and liquids and would provide a unique platform to explore fundamental questions related to liquid structure and gas solubility.
Although significant efforts have been made to fluidize porous solids in systems such as fluidized bed reactors, only limited efforts have been made to impart porosity to inherently fluid materials. In conventional liquids, tiny, transient voids form and collapse due to thermally induced density fluctuations, but the typical size of these voids is smaller than most guest molecules. This dynamic free volume affects many bulk properties of liquids, including gas solubility, but efforts to accurately probe and understand free volume are limited. In the nascent field of porous liquids, imparting true, gas-accessible porosity in liquids has relied on a steric approach in which solvent molecules are too large to enter the pores of a dispersed porous solid. This approach prevents the use of technologically relevant liquids such as water, necessitating a new method. Here, we describe our efforts to study and control both free volume and porosity in liquids, with a primary goal of understanding and increasing gas solubility in these systems.
