Investigating the Kinetic stability of Highly Confined Molecular Glasses Using in-situ Solvent Vapor Annealing

Nanocomposite films containing a substantial load of nanoparticles (NPs) hold great promise for various applications, such as structural coatings. Recently, capillary rise infiltration (CaRI) has emerged as a method to generate highly loaded nanocomposites. This process involves the penetration of interstitial gaps in densely packed NP films by polymers or molecular glasses, driven by capillarity. As NP diameter is decreased, increasing confinement leads to a significant rise in the glass transition temperature (Tg) and thermal resilience of the material. Here, we investigate the influence of nanoconfinement on the mechanisms and rate of solvent diffusion and uptake in Molecular Nanocomposites (MN) through in-situ solvent vapor annealing coupled with spectroscopic ellipsometry. N, N’-bis(3-methylphenyl)-N, N’-diphenylbenzidine (TPD) are infiltrated in silica NPs of diverse diameters as a model system, with toluene serving as a favorable solvent. Our findings reveal that reducing the pore size reduces the rate of solvent diffusion. Additionally, the diffusion process transitions from Case II, where solvent uptake occurs at a constant speed in the glassy material, to Fickian, even at elevated solvent vapor pressures, these results offer insight into the dynamical changes of glass in confinement and its role in decelerating the motion of solutes in the glassy matrix.