Mean interfacial molecular area

As the La-Hu transition proceeds, the mean interfacial molecular area drops and the mean area at the chain end of the molecule increases (2, 23). Effectively, the molecular volume has been subjected to a torque due to an expansive chain pressure relative to a net cohesive interaction near the head groups (4). This torque is conveniently described as a spontaneous curvature, C0 (4, 17), to a specific radius of curvature, R0 = 1/C0, at which point the net torque is almost zero. All Hu phases swell only to a limited degree. In a transition in coexistence with excess water, there is generally a change in the... 

When a protein molecule adsorbs, an area of interface of the order of 100 A has to be cleared for adsorption to occur (Section III,B). It seems reasonable to assume that once an adsorbed molecule has been compressed until its area in the interface, due to pressure displacement of segments, falls below this critical value, it will be unstable in the adsorbed state and will desorb. This transition state for desorption may be reached in two ways (1) at constant interfacial pressure and total area, by fluctuations in energy of the adsorbed molecules about the mean value, resulting in certain molecules achieving the transition state configuration (2) by compression of the film, thus increasing the interfacial pressure and decreasing the molecular area until the latter has been reduced to the critical value. 

This idea is a consequent transfer of the three-dimensional van der Waals equation into the interfacial model developed by Cassel and Huckel (cf. Appendix 2B.1). The advantages of Frumkin s position is a more realistic consideration of the real properties of a two-dimensional surface state of the adsorption layer of soluble surfactants. This equation is comparable to a real gas isotherm. This means that the surface molecular area of the adsorbed molecules are taken into consideration. Frumkin (1925) additionally introduced, on the basis of the van der Waals equation, the intermolecular interacting force of adsorbed molecules represented by a . 

The Gibbs equation allows the amount of surfactant adsorbed at the interface to be calculated from the interfacial tension values measured with different concentrations of surfactant, but at constant counterion concentration. The amount adsorbed can be converted to the area of a surfactant molecule. The co-areas at the air-water interface are in the range of 4.4-5.9 nm2/molecule [56,57]. A comparison of these values with those from molecular models indicates that all four surfactants are oriented normally to the interface with the carbon chain outstretched and closely packed. The co-areas at the oil-water interface are greater (heptane-water, 4.9-6.6 nm2/molecule benzene-water, 5.9-7.5 nm2/molecule). This relatively small increase of about 10% for the heptane-water and about 30% for the benzene-water interface means that the orientation at the oil-water interface is the same as at the air-water interface, but the a-sulfo fatty acid ester films are more expanded [56]. 

The mechanism of transfer of solute from one phase to the second is one of molecular and eddy diffusion and the concepts of phase equilibrium, interfacial area, and surface renewal are all similar in principle to those met in distillation and absorption, even though, in liquid-liquid extraction, dispersion is effected by mechanical means including pumping and agitation, except in standard packed columns. 

Electrodes represent an unrivaled platform onto which interfacial supramolecular structures can be assembled. They can be fully characterized before assembly and offer a convenient means to both probe and control the properties of the film. The interest in this area has increased dramatically in recent years because adsorbed monolayers enable both the nature of the chemical functional groups and their topology to be controlled. This molecular-level control allows the effects of both chemical and geometric properties on electron transfer rates to be explored. Moreover, these assemblies underpin technologies ranging from electrocatalysis to redox-switchable non-linear optical materials. 

Thermal molecular motion of PS at surfaces and interfaces in films was presented in this review. We clearly show that chain mobility at the surface region is more mobile than in the interior bulk phase and that chain mobility at the interfacial region is less than in the interior phase. This means that there is a mobility gradient in polymer films along the direction normal to the surface. This gradient can be experimentally detected if the ratio of the surface and interfacial areas to the total volume increases, namely in ultrathin films. 

The above considerations about the real adsorption system can be extended to the adsorption at the solid/liquid interface [16-22]. With regard to nonporous solids or solids with large pores the concept of specific surface area (the surface area divided by the mass of the solid) has a real physical meaning. Therefore, in such solid/fluid systems, the interfacial layer denotes the surface phase formed on the surface of a solid adsorbent. The macroscopic concept of the specific surface area loses physical meaning for microporous solids i.e., for the solids with pores of molecular dimensions [23]. The microporous adsorbents saturated by adsorbate molecules are rather considered as a uniphase system [24-25]. Cohsequently, the aforementioned concept of interfacial layer should be used most adequately with respect to uptake of fluids by microporous solids. 

In summary, the utility of micro-SERS spectroscopy for the evaluation of potential-dependent interfacial com-petititve and displacement reactions at chargwl surface has been demonstrated. The data obtained allow the determination of the chemical identity, structure, orientation, competitive and displacement adsorption of cationic surfactants and nitrophenol in the first adsorption layer. The examples of these measurements in the field of surfactants and organic pollutants reviewed in this article were selected to illustrate the sensitivity, molecular specificity of adsorption processes, accuracy, ease of substrate preparation, and manifold applications of Raman analysis. The spatial resolution of the laser microprobe, coupled with the 10 enhancement of the Raman cross-section, means that picogram quantities of material localized to pm-sized surfaces areas can be detected and identified by SERS vibrational spectroscopy. 

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