Interfacial solvation

The heterogeneity of the solvent at the interface introduces another degree of complexity in the problem. Molecular dynamics calculations have been able to give a molecular picture of the interfacial solvation of adsorbates but experiments have long been a chal-... 

For the remainder of this chapter, we discuss results for various studies of interfacial solvation dynamics. We first discuss studies at liquid liquid interfaces at planar interfaces and in microheterogeneous media in Section II. In Section III, we discuss solvation dynamics at liquid solid interfaces. In Section IV, we review theoretical models and simulations of solvation dynamics at liquid interfaces. Finally, we conclude with a discussion of future studies. 

Chandra and his coworkers have developed analytical theories to predict and explain the interfacial solvation dynamics. For example, Chandra et al. [61] have developed a time-dependent density functional theory to predict polarization relaxation at the solid-liquid interface. They find that the interfacial molecules relax more slowly than does the bulk and that the rate of relaxation changes nonmonotonically with distance from the interface They attribute the changing relaxation rate to the presence of distinct solvent layers at the interface. Senapati and Chandra have applied theories of solvents at interfaces to a range of model systems [62-64]. 

Given that interfacial solvation affects chemical transport/ surface reactivity and electron transfer/ and macromolecular self-assembly/ predictive models of solvent-solute interactions near surfaces will afford researchers deeper insights into a host of phenomena in biology, physics, and engineering. Research in this area should aid efforts to develop a general, experimentally tested, and quantitative understanding of solution-phase surface chemistry. 

Complementing the equilibrium measurements will be a series of time resolved studies. Dynamics experiments will measure solvent relaxation rates around chromophores adsorbed to different solid-liquid interfaces. Interfacial solvation dynamics will be compared to their bulk solution limits, and efforts to correlate the polar order found at liquid surfaces with interfacial mobility will be made. Experiments will test existing theories about surface solvation at hydrophobic and hydrophilic boundaries as well as recent models of dielectric friction at interfaces. Of particular interest is whether or not strong dipole-dipole forces at surfaces induce solid-like structure in an adjacent solvent. If so, then these interactions will have profound effects on interpretations of interfacial surface chemistry and relaxation. 

Figure 2.38 Interfacial solvation (a) a solvated molecule embedded in a cavity lying on top of a metal surface (b) a solvated molecule at the diffuse interface characterized by position-dependent properties, e.g. permittivity e(z).

Thermodynamic Basis for the Membranolytic Potential of Oxides Crystal Chemistry and Interfacial Solvation... 

The electrostatic attraction step can be examined using the Solution and Electrostatic (SE) model for ion adsorption.25 The model uses a thermodynamic approach based on crystal chemistry and interfacial solvation. The SE model was developed originally for oxide surface-small ion interactions,26 30 and cannot pretend to... 

THERMODYNAMIC BASIS FOR THE MEMBRANOLYTIC POTENTIAL OF OXIDES CRYSTAL CHEMISTRY AND INTERFACIAL SOLVATION... 

Computational studies of chemical reactions dynamics at liquid/vapor and liquid/liquid interfaces to date include the following types of reactions isomerization, photodissociation, acid dissociation, electron transfer, proton transfer, ion transfer, and nucleophilic substitution. These studies have been motivated by experimental observations and fundamental scientific interest in understanding how the unique surface properties affect chemical reactivity. Some of these studies have been reviewed.Here we present two examples selected to demonstrate the computational steps described above and their relation to the concepts developed in earlier sections. The focus is on contrasting the surface reactivity with that in the bulk and on examining surface effects in light of the knowledge about the structure and dynamics of neat interface and interfacial solvation, discussed earlier in the chapter. 

The answers which are discussed in this book are based on the following three concepts. The first one introduces ion specificity through collective dispersion type interactions an ion specificity is thereby obtained by the explicit consideration of the size and the polarisability of the ions. Based on molecular dynamics (MD) simulation with polarisable force fields, Jungwirth and Tobias state that induction interactions close to the free surface may be responsible for the preference of heavier ions at interfacial solvation sites. The asymmetric, incomplete solvation shell induces a sizable dipole on the anion at the interface, which is assumed to be the driving force for the interfacial propensity of the ions. MD simulation provides a very detailed picture of the interfacial architecture however, the results depend strongly on the interaction potentials which are not exactly known. Hence, experiments are needed to verify the predictions. Indeed, this task is challenging and many sophisticated surface analytical techniques, even when pushed to the limits, may still yield only inconclusive results. 

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