Dynamics of Nanoconfined Supercooled Liquids

Abstract

Near their glass transition temperature T(g), supercooled liquids display dramatic changes regarding the dynamics if subject to geometrical restrictions on the scale of 2 to 200 nm. Confinement-induced shifts of T(g) of 25 K have been reported, equivalent to relaxation times that differ by several orders of magnitude compared with the bulk liquid at the same temperature. Both acceleration and frustration of structural relaxations have been observed, and the effects can depend strongly on the physical and chemical properties of the interface, on soft versus hard confinement, and on the size and dimensionality of the confining topology. This review attempts to extract a unifying picture from the past 20 years of diverse observations that involve experiments, simulations, and model considerations.

2H NMR Studies on the Dynamics of Pure and Mixed Hydrogen-Bonded Liquids in Confinement

“…In many situations, HB liquids are, however, not found as abundant bulk materials, but in nanoscopically confined spaces. Then, it is important to consider that, in general, the properties of bulk and confined liquids are significantly different [1][2][3]. A prominent example is the freezing point of water, which is reduced in highly restricted geometries, depending on the size and hydroaffinity of the confinement [4].…”

“…Moreover, T 1,x and β 1,x denote the time constants and stretching parameters of the individual relaxation steps, respectively, so that the corresponding mean 2 H SLR times can be calculated according to 〈T 1,x 〉 = (T 1,x /β 1,x )Γ(1/β 1,x ), where Γ(x) is the gamma function. 2 H STE experiments provide access to slow molecular dynamics with correlation times 10 −5 s < τ < 10 0 s. This approach allows one to measure and to correlate the respective quadrupolar frequencies ω Q during two short evolution times t p , which are separated by a much longer mixing time t m . Specifically, it is possible to measure the rotational correlation functions [23,28]:…”

Slow dynamics in cylindrically confined colloidal suspensions

“…Many experiments show that glasses change their properties when their size is sufficiently small, both for small-molecule glasses and polymer glasses [8,[12][13][14]. One of the key observations is that the glass transition temperature T g changes for confined samples.…”

Solute location in a nanoconfined liquid depends on charge distribution

“…[9][10][11] An impressive diversity of frameworks has been synthesized that can confine liquids on nanometer length scales, including silicate glasses, reverse micelles, metal-organic frameworks, biological systems, and supramolecular assemblies. Each of these systems presents varied and tunable characteristicse.g., size, shape, surface chemistry, flexibility-that modify the structure and dynamics of the confined liquid.…”

“…[9][10][11][22][23][24] Thus, even small changes in reaction complex location can have important consequences for the reaction mechanism, barriers, and rate constants that are relevant to applications of mesoporous materials, for example, for catalysis or sensing. This provides a strong impetus to understand the relationship between solute charge distribution and location in nanoconfined solvents, including the key factors that influence this connection.…”