Shrinkage Dynamics of Organic Template Substances with Long Alkyl Chains toward Porous Material Design

Abstract

Templating with organic substances is known as a primary step for synthesizing silica-based porous materials, e.g., porous clay nanoheterostructures, but the shrinkage dynamics of template substances in response to temperatures and its influence on micro- and mesopore formation has not been the subject of extensive research. Here, the shrinkage of hexadecyltrimethylammonium (HDTMA+) monomers with long alkyl chains perceptible to temperatures is studied by means of molecular simulations coupled with angstrom-scale open-space analysis using positronium. The HDTMA+ monomers are deviated from trans conformation concomitantly forming ∼6 Å open spaces in the agglomerate upon coexisting with propanol molecules. Pore texture properties in view of micro- and mesopores, studied by N2 adsorption/desorption experiments at −196 °C, are found to be improved at low temperatures owing to efficient pillaring between two adjacent nanosheets resultant from less shrinkage of HDTMA+ monomers.