Nonassociated fluids

The main conclusion which can be drawn from the results presented above is that dimerization of particles in a Lennard-Jones fluid leads to a stronger depletion of the proflles close to the wall, compared to a nonassociating fluid. On the basis of the calculations performed so far, it is difficult to conclude whether the second-order theory provides a correct description of the drying transition. An unequivocal solution of this problem would require massive calculations, including computer simulations. Also, it would be necessary to obtain an accurate equation of state for the bulk fluid. These problems are the subject of our studies at present. 

As discussed in Chapter 3, the virial equation is suitable for describing vapor-phase nonidealities of nonassociating (or weakly associating) fluids at moderate densities. Equation (1) gives the second virial coefficient which is used directly in Equation (3-lOb) to calculate the fugacity coefficients. 

The singlet-level theory has also been used to describe the structure of associating fluids near crystalline surfaces [30,31,76,77]. The surface consists explicitly of atoms which are arranged on a lattice of a given symmetry. The fluid atom-surface atom potential can also involve an associative term, i.e., the chemical-type bonding of the adsorbate particles with the surface may be included into the model. However, we restrict ourselves to the case of a nonassociative crystalline surface first. 

The a-s-a and sp-s-sp cuts of the density profiles (Figs. 9(c) and 9(d)) clearly demonstrate that for a highly dimerized fluid the nonassociatively adsorbed dimers have a tendency to orient perpendicularly or slightly tilted... 

The calculations have been carried out for a one-component, Lennard-Jones associating fluid with one associating site. The nonassociative van der Waals potential is thus given by Eq. (87) with = 2.5a, whereas the associative forces are described by means of Eq. (60), with d = 0.5contact with an attracting wall. The fluid-wall potential is given by the Lennard-Jones (9-3) function... 

Note that, for = 0, the potential given above does not reduce to the Lennard-Jones (12-6) function, because the soft Lennard-Jones repulsive branch is replaced by a hard-sphere potential, located at r = cr. The results for the nonassociating Lennard-Jones fluid can be found in Ref. 159. 

Application to Strongly Absorbing Nonassociated Liquid V. Hat-Curved Model and Its Application for Polar Fluids... 

In the third period, which ended in 1999 after the book VIG was published, various fluids had been studied strongly polar nonassociated liquids, liquid water, aqueous solutions of electrolytes, and a solution of a nonelectrolyte (dimethyl sulfoxide). Dielectric behavior of water bound by proteins was also studied. The latter studies concern hemoglobin in aqueous solution and humidified collagen, which could also serve as a model of human skin. In these investigations a simplified but effective approach was used, in which the susceptibility % (m) of a complex system was represented as a superposition of the contributions due to several quasi-independent subensembles of molecules moving in different potential wells (VIG, p. 210). (The same approximation is used also in this chapter.) On the basis of a small-amplitude libration approximation used in terms of the cone-confined rotator model (GT, p. 238), the hybrid model was suggested in Refs. 32-34 and in VIG, p. 305. This model was successfully employed in most of our interpretations of the experimental results. Many citations of our works appeared in the literature. 

Models 1 and 2 were applied to simple nonassociated polar liquids. Wideband Debye relaxation + FIR spectral dependencies of the permittivity s (v) and absorption ot(v) were successfully described. Usually only one quasiresonance absorption band (at v between 10 cm-1 and 100-200 cm-1) and one non-resonance Debye loss e" peak (at microwaves) arise in these fluids. Although a spatial model gives, unlike a planar one, a correct value of the integrated absorption J ° ve"(v)dv, the calculated spectral dependencies resemble those found for motion in a plane. 

The hat-curved model also gives a satisfactory description of the wideband dielectric/FIR spectra of a nonassociated polar fluid (CH3F) (Fig. 25). It is worthwhile mentioning that only a poor description of the low-frequency (Debye) spectrum could be accomplished, if the rectangular potential were used for such a calculation [32] see also Section IV.G.3. Unlike Fig. 25b, the estimated peak-loss frequency does not coincide38 in this case with the experimental frequency vD. 

Modern theory of associative fluids is based on the combination of the activity and density expansions for the description of the equilibrium properties. The activity expansions are used to describe the clusterization effects caused by the strongly attractive part of the interparticle interactions. The density expansions are used to treat the contributions of the conventional nonassociative part of interactions. The diagram analysis of these expansions for pair distribution functions leads to the so-called multidensity integral equation approach in the theory of associative fluids. The AMSA theory represents the two-density version of the traditional MSA theory [4, 5] and will be used here for the treatment of ion association in the ionic fluids. 

Campbell TC, Chen J, Liu C, Li J, Parpia B (1990) Nonassociation of aflatoxin with primary liver cancer in a cross-sectional ecological survey in the Peoples Republic of China. Cancer Res 50 6882-6893 Chao SH, Suzuki Y, Zysk JR, Cheung WY (1984) Activation of calmodulin by various metal cations as a function of ionic radius. Mol Pharmacol 26 75-82 Chatter]ee MS, Abdel-Rahman M, Klein P, Bogden J (1988) Amniotic fluid cadmium and thiocyanate in pregnant women who smoke. J Reprod Med 33 417-420... 

Abdoul, W. Rauzy, E. Peneloux, A. (1991). Group-contribution equation of state for correlating and predicting thermodynamic properties of weakly polar and nonassociating mixtures. Binary and multicompwnent systems. Fluid Phase Equilib., V0I.68, pp. 47-102... 

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