Phase separation of triethylamine and water in native and organically modified silica nanopores.

A mixture of triethylamine and water is a lower critical solution temperature system that demixes (separates into individual phases) on heating. Differential scanning calorimetry has been applied to study the process of demixing in native and organically modified silica nanopores whose size varied from 4 to 30 nm. It has been found that in both types of nanopores, the temperature and enthalpy of demixing decrease significantly with decreasing the pore size. Isoconversional kinetic analysis has been utilized to determine the activation energy and pre-exponential factor of the process. It has been demonstrated that the depression of the transition temperature upon nanoconfinement is associated with acceleration of the process due to lowering of the activation energy. Nanoconfinement has also been found to lower the pre-exponential factor of the process that has been linked to a decrease in the molecular mobility.

Melting of gelatin gels confined to silica nanopores.

Nanoconfinement is a way to create materials whose properties differ from the bulk. For the first time, this research explores the effect of nanoconfinement on the thermodynamics and kinetics of gel melting. Differential scanning calorimetry has been employed to study gelatin gels prepared inside 4, 6, 15, and 30 nm pores of a silica matrix. It has been found that with decreasing the pore size the heat of melting decreases from 3.5 J g-1 in bulk to 0.6 J g-1 in 6 nm pores, which is linked to a decrease in crosslinks formed via hydrogen bonding. Despite decreases in crosslink formation, the melting temperature for gels confined to 6 nm pores increased nearly 10 °C compared to bulk gel. In 4 nm pores, no gel melting was observed. Isoconversional kinetic analysis of the melting data has revealed that the increase in thermal stability is associated with a decrease in the pre-exponential factor that occurs upon nanoconfinement. The origins of the effect have been linked to diminished molecular mobility of the gelatin chains confined inside the nanopores, which leads to enhanced restoration of broken crosslinks.