Characterization of Adsorption-Induced Deformation Behaviors in Microporous Dipodal Organosilane-Based Hybrid Silica Films

Abstract

The distinctively high surface area of nanoporous solids (pore size <100 nm) makes them one of the most relevant classes of materials in adsorption-related applications. During vapor adsorption, stresses arising at the fluid–solid interface due to strong interactions within a confined space ultimately lead to strain. This effect is particularly pronounced in micropores (pore size <2 nm), where fluid confinement is the strongest. Understanding and modeling adsorption-induced deformation (AID) is crucial for the optimal design of functional materials and requires experimental validation using well-defined model systems. Hereby, we report a rapid and surfactant-free dip-coating process, allowing the reproducible synthesis of homogeneous microporous films using dipodal organosilane precursors, of which the organic fraction serves as a sacrificial porogen. After conducting a precursor selection process using materials prepared by solvent casting, two purely microporous and one micro/mesoporous thin films were prepared by dip-coating. Using environmental ellipsometry porosimetry (EEP), known for its exceptional thickness sensitivity, the strain of the films induced by water sorption was assessed over controlled ranges of relative humidity, revealing different sorption/deformation behaviors for each material. This work demonstrates the potential of combining sol–gel chemistry, dip-coating, and EEP for the efficient acquisition of large quantities of simultaneous adsorption and deformation data that may be used for the validation of AID models.