Carbon-13 NMR Study of the Effect of Confinement on the Molecular Dynamics of 2-Ethylhexyl Benzoate

Abstract

Spin-lattice relaxation times of individual carbons in 2-ethylhexyl benzoate (EHB) in bulk and confined to porous silica glasses of pore radii of 33, 52, and 102 Å were measured as a function of temperature from +40 to -51 °C. The two-state fast exchange model was successfully applied, in the wide temperature range including beyond the motional narrowing regime, to determine the spin-lattice relaxation times of the molecules in the surface layer (T1S) as a function of temperature. The Cole-Davidson distribution model was used to analyze the relaxation data for both the bulk (T1B) and surface layer (T1S) of the confined liquid. The line broadening of confined EHB at lower temperatures below -21 °C inherently limited the temperature range over which T1S could be estimated and prevented the quantitative analysis of T1S by the model. Through the phenomenological comparison of T1S with T1B in terms of the parameters of the Cole-Davidson model, it was found that the motional behavior of the phenyl ring part of the EHB molecule was significantly affected by the surface interaction and the effect is smaller for the flexible alkyl chain. Small temperature dependence of the relaxation rate of T1S at motional narrowing regime showed a characteristic feature of liquid diffusing on a two-dimensional surface. In addition, the results of the quantitative analysis of T1B were compared with a previous experiment performed as a function of pressure.

Molecular dynamics of tert-butyl chloride confined in CPG studied by NMR

“…that the C 0 3 reorientation is described by different activation parameters the experimental data were fitted to Eqs. (1) and (2). The results are shown by solid and dashed lines, respectively, in Figs.…”

“…Systems of a liquid guest filled in the pores of silica materials are an interesting model for the study of the influence of geometrical restrictions and surfaces on the phase behaviour, surface-liquid and surface-solid interactions, as well as molecular motions of the confined molecules [1][2][3][4][5][6]. A well known example of the mesoporous silica materials are CPG characterized by high surface area and narrow pore size distribution.…”

“…At lower temperature the molecules in this phase exhibit an increased rotational mobility comparing to the molecules in the crystalline phases [12,13]. The molecules at the interior of the pore solidifies at a reduced temperature [14] and are expected to have similar properties as the bulk liquid [2,[15][16][17].…”

Dynamics of confined methyl iodide studied by Raman spectroscopy

“…app is obtained by curve fitting of mathematically generated composite lines of two Lorentzians according to Eqn(6). app is obtained by curve fitting of mathematically generated composite lines of two Lorentzians according to Eqn(6).…”

Molecular Dynamics of Tert-butyl Chloride Confined to CPG (7.4, 15.6 nm)

“…Confined geometry has generated much interest in many fields of applied and fundamental research. It is well recognized that the characteristic features of the molecular motion and the thermal properties as well as the spatial structure of solids can be modified by the proximity of an interface, which provides geometrical constraints on the material [3][4][5][6][7][8]. The low dimensionality and fluid-wall interactions lead to the formation of a highly defective nature of the crystallites or pseudo-liquid within the porous medium.…”