Confinement Effects on Glass-Forming Aqueous Dimethyl Sulfoxide Solutions

Abstract

Combining broadband dielectric spectroscopy and nuclear magnetic resonance studies, we analyze the reorientation dynamics and the translational diffusion associated with the glassy slowdown of the eutectic aqueous dimethyl sulfoxide solution in nano-sized confinements, explicitly, in silica pores with different diameters and in ficoll and lysozyme matrices at different concentrations. We observe that both rotational and diffusive dynamics are slower and more heterogeneous in the confinements than in the bulk but the degree of these effects depends on the properties of the confinement and differs for the components of the solution. For the hard and the soft matrices, the slowdown and the heterogeneity become more prominent when the size of the confinement is reduced. In addition, the dynamics are more retarded for dimethyl sulfoxide than for water, implying specific guest-host interactions. Moreover, we find that the temperature dependence of the reorientation dynamics and of the translational diffusion differs in severe confinements, indicating a breakdown of the Stokes–Einstein–Debye relation. It is discussed to what extent these confinement effects can be rationalized in the framework of core-shell models, which assume bulk-like and slowed-down motions in central and interfacial confinement regions, respectively.

NMR studies on the influence of silica confinements on local and diffusive dynamics in LiCl aqueous solutions approaching their glass transitions

“…Moreover, we exploit that analogous studies on bulk LiCl solutions 28 and neat D 2 O in silica pores 34 determined the hydrodynamic radii of R H = 1.05 Å for the lithium ions and R H = 1.35 Å for the water molecules. These values are smaller than expected based on the particle sizes, in agreement with findings for other bulk and confined hydrogen-bonded liquids, 48,58 suggesting that a complex transport mechanism leads to a mild retardation of translational diffusion relative to rotational motion.…”

“…Thus, we find no evidence for a breakdown of the SED relation for the confined LiCl solutions at the studied temperatures. Such a breakdown was reported for neat water in the same confinements, 34 whereas ethylene glycol 58 and aqueous dimethyl sulfoxide solutions 48 in silica pores obeyed the SED relation. For 1 H, the agreement of the rotational correlation times and the self-diffusion coefficients means that proton transport, which occurs independent of water transport, e.g., in a Grotthusslike mechanism, is of minor importance, and hence, our 1 H SFG results are dominated by the diffusion of water molecules.…”

“…In all pores, we observed a coupling of short-range and longrange dynamics, consistent with the SED relation. Previous studies reported that the SED relation is also obeyed by other confined hydrogen-bonded liquids 48,58 with the notable exception of water. 34 Another important difference between the salt solution and neat…”

“…When comparing SLR and STE results, it is important to consider that τ cc n and τ k n are not equivalent when molecular dynamics are characterized by nonexponential correlation functions, in particular, when broad distributions of correlation times exist. Therefore, it proved to be useful to determine peak correlation times τp,n, 33,47,48 which correspond to the peak positions of the related dynamic susceptibilities and approximate the most probable of the distributed correlation times. For the symmetric distributions associated with the CC form, τp,n = τ cc n , while the peak correlation times associated with stretched exponential decays can be obtained from 47 τp,n…”

Hydrogen-bond network distortion of water in the soft confinement of Nafion membrane

“…13 , the detected photon ux dN , for an incoming photon current density j 0 , is written as 21 dN = j 0 d 2 σ dΩdϵ dΩdϵ (1) where the dierential cross section is given by:…”