Resolving liquid-to-glass transitions of water under soft nanoconfinement

Abstract

Abstract Water has challenged scientists with numerous anomalies and confounding problems since the very early times. The kinetic glass transition of bulk water is a pristine example, as its location remains mostly inaccessible to experimentalists in an area below about −41 °C, where bulk water spontaneously crystallises. Confining water within nanometre-sized domains is an intriguing approach inspired by the cellular environment in nature to completely prevent crystallisation. Here we probe the existence of liquid-to-glass transitions of water nanoconfined between non-freezing lipidic bilayers and find a peculiar and counterintuitive regime over an extended temperature range, for which a sub-nanometre layer of water remains glassy in between fluid (mobile) walls of lipidic molecules. We provide comprehensive evidence for a slowing down of water dynamics under soft nanoconfinement occurring in the −63 to −20 °C range across six orders of magnitude in time scales from 10 −6 to 10 −12 s, and a static glass transition ranging between −74 and −64 °C. These findings provide important insights into the elusive glass transition of water under nanoconfinement, with broader implications for all those areas where water is confined at the nanometre scale below its freezing point.