Phase coexistence properties, solid-fluid

There are many cases in which other techniques have been applied to biphasic systems in order to establish the nature of mixing. For example, fluorescence microscopy of DPPC monolayers containing 2% of a fluorescent probe have shown the coexistence of solid and fluid phases of DPPC at intermediate pressures (Weis, 1991). Similar results have been achieved with a variety of other phospholipids using the same technique (Vaz et al., 1989). The recent application of laser light scattering to this area (Street et al., unpublished data) has yet to produce any conclusive evidence, but the future for this particular technique is also promising. It also provides information about the viscoelastic properties of the monolayer and how these are affected by the inclusion of penetration enhancers. 

Expressions obtained for the free energy, pressure and chemical potentials can be used to study the thermodynamic properties of the electrolyte solutions, in particular, to describe the phase diagram of ionic fluids. Such a possibility is illustrated in Fig. 7, which shows the effect of ion pairing on liquid-liquid coexistence curve in the ion-dipole model as a function of the ion concentration a = ()%/(pi + ps) and reduced temperature T = (Ms)-1/2, bs = Rpl/Rl The solid line corresponds to the ion-dipole model with the parameter of ion association, B = 10. The dashed line corresponds to the ion-dipole... 

Wetting phenomena in porous solids involve three coexisting phases fluid (hquid A or gas), liquid B and solid. In order to describe the interfacisil properties of such systems one needs three interfacial tensions, 7j , 7,j, and 7 ,> pertaining to the liquid-fluid-, solid-liquid-and solid-fluid interfaces, respectively. 

In order to use the above expressions for calculating the thermodynamic properties, appropriate expressions for the radial distribution function and for the equation of state for the hard-sphere reference system are required which are given in Appendix A. Fortunately, accurate information for the hard-sphere fluid as well as for the hard-sphere solid is available and this enables the determination of the properties of the coexisting dilute and concentrated phases of colloidal dispersions. 

The coexistence curves and properties of confined fluid were extensively studied by computer simulations. Shift of the parameters of the liquid-vapor critical point of fluids in pores was seen in many simulation studies. The most accurate results were obtained by simulations of LJ fluid in the Gibbs ensemble [10, 28-30, 32, 127, 141, 186, 187, 205, 249,250,262,274,325,326], but this method is restricted to the pores of simple geometry only. In the narrow slit pore with weakly attractive walls and widths of 6,7.5, and 10 a, the liquid-vapor critical point of LJ fluid decreases to 0.8897] , 0.9197] , and 0.9577] , respectively [325, 326]. For comparable fluid-wall interaction, the liquid-vapor critical temperature is about 0.9647] and 0.9817] in the pores with a width Hp= 12 a and 77p = 40(7, respectively [29]. The dependence of the pore critical temperature on the pore width is shown in Fig. 53. This dependence may be satisfactorily described by equation (15) (solid line) when we take into account that centers of molecules do not enter an interval of about 0.5 <7 near each wall. The critical temperatures of U fluid in the pores with strongly attractive walls are noticeably lower than in pores with weakly attractive walls (compare circles and squares in Fig. 53) [325,326]. This should be attributed to the effective decrease in the pore width due to the appearance of adsorbed film on the pore walls, which is almost identical in both phases. In this case, dependence of Tc p on Hp may be satisfactorily described by equation (15) (dashed line) if we take into account that... 

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