Impact of Interface Modification on the Behavior of Phenyl Alcohols within Silica Templates

Herein, thermal and dynamical properties, as well as host-guest intermolecular interactions, and the wettability of a series of monohydroxy phenyl-substituted alcohols (PhAs) infiltrated into native and silanized silica mesopores (of pore diameter, d similar to 5 nm) were investigated by means of dielectric and infrared (IR) spectroscopy, differential scanning calorimetry, and contact angle measurements. Calorimetric data showed the occurrence of the two glass transition temperatures, T-g. Importantly, around the one detected at higher temperatures (T-g,T-interfacial), a strong deviation in the temperature evolution of the relaxation time of the main process was observed for all systems. Moreover, an additional mode unrelated to the mobility of the interfacial layer and core molecules was revealed. One can suppose that it could be connected to either the slow Arrhenius process (SAP, previously reported for the polymer thin films) or the mobility of hydrogen-bonded structures. Further, IR investigations showed that the applied nanoconfinement had little impact on the strength of the hydrogen bonds (HBs), but it influenced the HBs' distribution (including the 'new' population of HBs) and the degree of association. Additionally, for the first time, we calculated the activation energy values of the dissociation process for PhAs in mesopores, which turned out to be lower with respect to those estimated for bulk samples. Thus, our research clearly showed the impact of the spatial geometrical restriction on the association process in alcohols having significant steric hindrance.