Heat Effects of Forced Water Intrusion in KIT-6 Grafted with Octyl and Perfluorooctyl Chains by Scanning Transitiometry

This article presents the heat evolved under the forced intrusion of water into hydrophobic grafted KIT-6 mesoporous silica with either alkyl or perfluorinated alkyl chains by scanning transitiometry. The experiments were conducted with two different calorimetric configurations. The first applied only a single active calorimeter cell experiencing a constant change in the rate of pressurization (dp/dt)T or a constant rate of compression (dv/dt)T. The second application is the dual active cell, where both the measuring and the reference cells experience the same changes in pressure and compression. It was found that the dual cell configuration is the best arrangement for pressure scanning calorimetry experiments, preventing the smearing of the heat effects from intrusion into the baseline heat. The average heat of high-pressure intrusion of water into hydrophobic KIT-6 was determined to be −8.5 ± 1.5 J·g–1 for alkyl grafting and −9.4 ± 0.9 J·g–1 for the perfluoroalkyl one. Perfluoroalkyl grafting was found to be the most resilient to degradation from exposure to repeated high-pressure water intrusion/extrusion cycling. Therefore, to accurately measure the heat released during the intrusion of nonwetting liquids into hydrophobic mesoporous materials, this article recommends using pressure scanning with a dual-cell differential configuration, which subtracts heat smearing effects from the signal, which otherwise remain in a single-cell configuration.