Intermolecular forces, theory

Intermolecular forces theory van der Waals forces bond the molecules together at the newly sheared surfaces of the particle boundaries. Microcrystalline cellulose is believed to undergo significant hydrogen bonding during tablet compression. ... 

The intermolecular forces theory and the liquid-surface film theory are believed to be the major bonding mechanisms in tablet compression. Many pharmaceutical formulations require a certain level of residual moisture to produce high quality tablets. The role of moisture in the tableting process is supported by the liquid-surface film theory. 

Stone A J 1996 The Theory of Intermolecular Forces (New York Oxford)... 

Claverie P 1971 Theory of intermolecular forces. I. On the inadequacy of the usual Rayleigh-Schrddinger perturbation method for the treatment of intermolecular forces Int. J. Quantum Chem. 5 273... 

Margenau H and KesPierN R 1971 Theory of Intermolecular Forces 2nd edn (New York Pergamon)... 

Stillinger F 1973 Structure in aqueous solutions from the standpoint of scaled particle theory J. Solution Chem. 2 141 Widom B 1967 Intermolecular forces and the nature of the liquid state Sc/e/ ce 375 157 Longuet-Higgins H C and Widom B 1964 A rigid sphere model for the melting of argon Mol. Phys. 8 549... 

It follows from this discussion that all of the transport properties can be derived in principle from the simple kinetic dreoty of gases, and their interrelationship tlu ough k and c leads one to expect that they are all characterized by a relatively small temperature coefficient. The simple theory suggests tlrat this should be a dependence on 7 /, but because of intermolecular forces, the experimental results usually indicate a larger temperature dependence even up to for the case of molecular inter-diffusion. The Anhenius equation which would involve an enthalpy of activation does not apply because no activated state is involved in the transport processes. If, however, the temperature dependence of these processes is fitted to such an expression as an algebraic approximation, tlren an activation enthalpy of a few kilojoules is observed. It will thus be found that when tire kinetics of a gas-solid or liquid reaction depends upon the transport properties of the gas phase, the apparent activation entlralpy will be a few kilojoules only (less than 50 kJ). 

The conneetions between students ideas and scientific conceptions are less tight than above. Especially in the case of intermolecular forces, the eontexts that lead to the development of the theory are extremely eomplex and too complieated for school. Nevertheless, a historical embedding eould help students to reeognize the foeus and the limitations of the theories. 

A. J. Stone (1991) The Theory of Intermolecular Forces (Oxford University Press, Oxford). An extensive survey of the applications of quantum mechanics to determine the forces between molecules. 

He is the author of two other books. Nonequilibrium Thermodynamics (1962) and Vector Analysis in Chemistry (1974), and has published research articles on the theory of optical rotation, statistical mechanical theory of transport processes, nonequilibrium thermodynamics, molecular quantum mechanics, theory of liquids, intermolecular forces, and surface phenomena. 

Stone AJ (1996) The theory of intermolecular forces, Oxford University Press, Oxford... 

Plasticization has been explained by a variety of theories in an attempt to explain how the plasticizer reduces the rigidity of the final part. All theories rely on the premise that the plasticizer reduces the strength of the intermolecular forces between the polymer chains. The theories fall into two broad categories interference mechanisms and expansion mechanisms. The interference mechanisms state that plasticizer molecules interact only weakly with the polymer chains after separating the chains from one another, thereby reducing the overall cohesion of the material. The expansion mechanisms state that the reduced rigidity arises from an increase in the free volume of the system as the system expands to incorporate bulky,... 

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... 

Intermolecular Forces and Their Evaluation by Perturbation Theory... 

The liquid state is a condensed state, so each molecule is always interacting with a group of neighbours although diffusing quite rapidly. As a result, although momentum through a shear plane still occurs, it is a small contribution when compared to the frictional resistance of the molecules in adjacent layers. It is the nature of this frictional resistance that we must now address and it will become clear that it arises from the intermolecular forces. The theories of the viscosity of liquids are still in an unfinished state but the physical ideas have been laid down. The first... 

Like other measures of pressure, c has units of MPa. In theory, a liquid will break all solvent-solvent interactions on vaporization, and so c is a measure of the sum of all the attractive intermolecular forces acting in that liquid. Hydrogen-bonding and dipolar solvents therefore have high c values. Water has a large value for c, and fluorocarbons very low values (Table 1.5). 

The program of calculating the BO-level potentials from Schroedinger level cannot often be carried through with the accuracy required for the intermolecular forces in solution theory. (9.) Fortunately a great deal can be learned through the study of BO-level models in which the N-body potential is pairwise additive (as in Eq. (3)) and in which the pair potentials have very simple forms. (2, 3, 6) Thus for the hard sphere fluid we have, with a=sphere diameter,... 

The theory of molecular interactions has been reviewed extensively in the past and many monographs and contributed volumes are available in this field. Three of them45-47) are especially recommended because they give the same kind of insight into the problems that is needed here. We do not intend to present an extensive discussion on the methods applied to intermolecular forces in this paper. The interested reader will be referred to some selected articles. Nevertheless it seems necessary at least to introduce the type of notation we prefer here and to stress some points that we feel to be important for a critical evaluation of the calculated results. 

Quantum mechanical calculations of intermolecular forces generally start from wave functions of the isolated particles. With regard to the actual treatment of the interaction, however, there is some competition between perturbation theory and MO methods. 

Before we tarn to MO theory of molecular interactions a short discussion on the reliability of semiempirical calculations of the CNDO type by means of perturbation theory would be useful. For a better understanding of the possibilities and limitations of semiempirical MO approaches to intermolecular forces we calculated first-order perturbation energies for very simple complexes with and... 

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