The Neat Interface

Molecular dynamics simulations have consistently provided pictures of microscopically corrugated liquid/liquid boundaries at the picosecond time scale, as exemplified in Figure. The characteristic width of the neat interface... 

Most simulation techniques applied to date to liquid interfaces are based on classical molecular dynamics and Monte Carlo methods. With few exceptions (discussed below), these techniques can be used straightforwardly to simulate the neat interface between a liquid and a second phase and to investigate the thermodynamics and dynamics of solute adsorption and reaction. There are several excellent books on the fundamentals of these techniques as well as free software available on the internet. (For a library of free software, see http //www.ccp5.ac.uk/librar.shtml.)... 

Statistical mechanical approaches to the structure of the neat interface generally employ some approximations of the pair distribution function to develop a theory of density profile or surface tension. An example of such an approximation is using the pair distribution of the homogeneous liquid at the density appropriate to the location z. For a direct calculation of p r, z, 9), one... 

Dependence on probe location and orientation. Prom our discussion of the neat interface we now know that this region is very narrow, and the SHG peak spectrum will likely depend strongly on the solute location and orientation. This was proved by Steel and Walker who designed a series of surfactant solvatochromic probes they call molecular rulers.Each of these surfactant molecules consists of an anionic hydrophilic sulphate group (which is restricted to the aqueous phase), attached to a hydrophobic solvatochromic probe moiety by a variable length alkyl spacer. The probe is based on para-nitroanisole (PNA), whose bulk solution excitation maximum shifts monotonically with solvent polarity. When these surfactant molecules adsorb at the interface, the anionic end is in the aqueous phase, and the probe moiety resides at variable positions relative to the interface. 

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