Water Structure and Dynamics at a Silica Surface: Pake Doublets in ¹H NMR Spectra

Abstract

Detailed knowledge about the dynamics and structure of liquids in the vicinity of a solid surface is important in several fields of research. In this study a homogeneous model system of colloidal and nonporous silica particles with a narrow particle size distribution was used to examine such properties of adsorbed water and 1-heptanol. Doublet (1)H water resonances ("Pake doublets") indicate a preferred spatial orientation for the water molecules, as well as a lower molecular density in the surface-induced water structures compared to bulk water. These surface-induced structures are found to extend at least 8 nm from the silica surface. T(1) relaxation measurements at several temperatures indicate weaker H-bonding in the adsorbed water compared to bulk water. T(2) relaxation measurements at several temperatures reveal the presence of two water phases and give quantitative information on the mobility of water molecules and proton exchange processes. The presence of 1-heptanol changes the water characteristics, primarily in the water phase closer to the surface, where water molecules experience decreased translational and increased rotational freedom. In the absence of water, adsorbed 1-heptanol forms surface aggregates encompassing several molecular layers, where the first adsorbed layer shows severe restrictions in mobility and subsequent layers are more mobile.

Water immobilization by glass microspheres affects biological activity

“…Again, this effect was solely dependent on the amount of glass surface area present in the suspensions (Figure S7 ). Such T 2 thermal behavior has been previously reported for pure water and silica-water systems where observed T 2 values are dominated by exchange contributions 7 , 10 . The T 1 behavior is also consistent with previous reports 7 , 10 .…”

“…This increase in the amount of bound water was correlated with an increase in the monolayer amount of bound water using water activity measurements (Figure S3B ). T 2 measurements are ideal for the study of surface interactions of water and can provide insight on chemical exchange 7 . Results obtained in this study are consistent with atomic scale molecular dynamics computer simulations and experimental results of water molecules on amorphous silica surfaces 8 , 9 .…”

Silica Surface Features and Their Role in the Adsorption of Biomolecules: Computational Modeling and Experiments

“…In the presence of silica, 1 H NMR relaxation times were used to evidence surface-induced water structures characterised by a preferred spatial orientation of the water molecules, and a lower molecular density (as compared to bulk water). 202 These surfaceinduced structures extend at least 8 nm from the surface. It follows that for a suspension of divided silica with a surface area in the range of several hundred m 2 g -1 , the amount of modified water will represent several times the weight of the silica.…”

Identification of Proton Populations in Cherts as Natural Analogues of Pure Silica Materials by Means of Low Field NMR

“…T 1 and T 2 distributions from 1 H MAS NMR of nonporous silica yielded information about molecular dynamics and interactions of fluid particles with the adsorbent’s surface (different relaxation times for subsequent layers of water, cross-polarization). 56 These colloidal silica particles can be used as a model of water- or 1-heptanol-bearing rocks. NMR spectroscopy ( 29 Si MAS NMR) also helped to trace the depolymerization process of amorphous silica due to ASR (alkali silica reaction) reaction on the grounds of dominant peak location (the Q 4 peak disappeared and a Q 3 , Q 2 or Q 1 peak appeared).…”