Intermolecular forces short-range

Generally speaking, intermolecular forces act over a short range. Were this not the case, the specific energy of a portion of matter would depend on its size quantities such as molar enthalpies of formation would be extensive variables On the other hand, the cumulative effects of these forces between macroscopic bodies extend over a rather long range and the discussion of such situations constitutes the chief subject of this chapter. 

Many of these features are interrelated. Finely divided soHds such as talc [14807-96-6] are excellent barriers to mechanical interlocking and interdiffusion. They also reduce the area of contact over which short-range intermolecular forces can interact. Because compatibiUty of different polymers is the exception rather than the rule, preformed sheets of a different polymer usually prevent interdiffusion and are an effective way of controlling adhesion, provided no new strong interfacial interactions are thereby introduced. Surface tension and thermodynamic work of adhesion are interrelated, as shown in equations 1, 2, and 3, and are a direct consequence of the intermolecular forces that also control adsorption and chemical reactivity. 

In a classical simulation a force-field has to be provided. Experience with molecular liquids shows that surprisingly good results can be obtained with intermolecular potentials based on site-site short-range interactions and a number of charged sites... 

The intermolecular forces operative in nonpolar compounds are also electrostatic-in nature. These weak van der Waals forces involve attraction between nonbonded atoms and are effective over short ranges only. 

The dynamic behavior of reactions in liquids may differ appreciably from that of gas phase reactions in several important respects. The short-range nature of intermolecular forces leads to several major differences in the macroscopic properties of the system, often with concomitant effects on the dynamics of chemical reactions occurring in the liquid phase. 

Although the trajectory and convective diffusion techniques are conceptually simple, certain mechanisms, in particular, the exact role of the intermolecular force between the particle and the electrode remains an element of debate. Most of these problems arise because continuum models about short-range interactions break down at very short distances, where other factors, much less defined come into play. A complete understanding of the coelectrodeposition process requires a synergy between theoretical models and thorough experimental work. 

It is convenient, although artificial to divide intermolecular forces into two types - long-range (van der Waals) forces and short-range (valence or chemical) forces. 

The required specialized distribution functions are quite analogous to those which are currently of interest in the theory of fluids with short-range intermolecular forces (see Squire and Salsburg81 and references therein). We require the probability that a set n of defects shall be in a configuration n with the restriction that none of the remaining (N — n) defects are on a particular set of sites b out of the total B sites of the crystal. This probability may be written as... 

A consequence of the intermolecular forces is that any molecule in the liquid state has a large coordination number so that the structure has a low energy configuration. In other words there is short-range order in the liquid state. A significant amount of work must be done to remove a molecule from this structure - the latent heat of vaporisation. 

These results shown in Figures 1 and 2 demonstrate the similarity of the effects of short-range forces on the properties of nonelectrolytes and concentrated electrolytes. One finds both positive and negative deviations from ideality and these effects may be ascribed to the difference between the intermolecular potential energy of attraction of unlike species to the mean of the corresponding potentials for pairs of like molecules. Previous discussion of these systems has focused on the hydration of the positive ion as the dominant effect, but we see in Figure 1 that... 

The molecular approach, adopted throughout this book, starts from the statistical mechanical formulation of the problem. The interaction free energies are identified as correlation functions in the probability sense. As such, there is no reason to assume that these correlations are either short-range or additive. The main difference between direct and indirect correlations is that the former depend only on the interactions between the ligands. The latter depend on the maimer in which ligands affect the partition function of the adsorbent molecule (and, in general, of the solvent as well). The argument is essentially the same as that for the difference between the intermolecular potential and the potential of the mean force in liquids. 

The traditional method of dealing with irreversible processes is, of course, the use of the Boltzmann integro-differential equation and its various extensions. But this method leads to two serious difficulties. The first is that Boltzmann s equation is neither provable nor even meaningful except in the context of molecular encounters, i.e., under the assumption that the intermolecular forces are of such short range in comparison with molecular distances that a molecule spends only a negligible fraction of its time within the influence of others. This drastically restricts the field of applicability, confining the treatment to gases close to the ideal state. But even then the equation can only be established on the basis of an essential assumption of molecular probabilistic independence ( micromolecular chaos ).3... 

In the case of the flux of mass, the result is the normal component of pua. But for the flux of momentum and energy, in general the flux density is not the normal component of a vector or tensor function of (t, x), since it will depend on the extended shapes of if and Y. But in the case of short-range forces and slowly varying p, ua, E, it can be shown to have this form with sufficient approximation. Thus one is led to the familiar pressure tensor and heat flow vector Qa, both as functions of (t, x). It is to be emphasized that the general expression of these quantities involves not only expected values of products of momenta (or velocities), but the effect of intermolecular forces. 

In actuality, molecules in a gas interact via long-ranged attractions and short-range repulsive forces. An interaction potential energy function is used to describe these forces as a function of intermolecular distance and orientation. This section introduces two commonly used interaction potential energy functions. 

We suggest to employ the parameter / as some measure of localization of intermolecular interactions—that is, of a spread of short-range forces in a liquid The lower the value of f the stronger these forces at larger distances. We estimate roughly this spread as a linear length of the curved part (1 —/)p of the well ... 

The short-range intermolecular forces which are responsible for surface/interfacial tensions include van der Waals forces (in particular, London dispersion forces, which are universal) and may include... 

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