The glass transition and the dynamics of water within pectin and metal–organic framework nanochannels

Abstract

The glass transition temperature (Tg) of water confined in nanoscale environments critically influences its dynamics and structure, thereby impacting the design of sustainable materials. Determining Tg in different confinement matrices remains challenging owing to variations in pore chemistry and geometry. Here, we investigated water confined within calcium-cross-linked pectin (PE–Ca) and metal–organic framework (Fe–BTC) nanochannels using differential scanning calorimetry, broadband dielectric spectroscopy, and FT-IR spectroscopy. We found that confined water exhibited a Tg between 170 and 200 K, with PE–Ca showing a higher Tg (193 K) than Fe–BTC (170 K), correlating with differences in the hydrogen bonding networks. Water in pectin forms a network similar to that of bulk water, whereas Fe–BTC confinement induces distorted structures with strong interfacial hydrogen bonds. These findings suggest that the Tg of bulk water is higher than that previously reported (∼136 K) and highlight how confinement chemistry governs water dynamics, informing the development of eco-friendly materials and advancing our understanding of supercooled water.