Landau theory definition

From the point of view of statistical mechanics there are many problems, such as strongly anharmonic lattices, to which the theory can be applied.14 It appears as a natural generalization of Landau s theory of quasi-particles in the case when dissipation can no longer be neglected. The most interesting feature is that equilibrium and nonequilibrium properties appear linked. The very definition of the strongly coupled anharmonic phonons depends on their lifetime. 

For more than half of century the classical theories by Debye and Hiickel as well as by Derjaguin, Landau, Verwey and Owerbeek (DLVO) have been at the basis of theoretical physical chemistry and chemical engineering. The substantial progress in material science during last few decades as well as the advent of new instrumentation and computational techniques made it apparent that in many cases the classical theories break down. New types of interactions (e.g. hydrodynamic, entropic) have been discovered and a number of questions have arisen from theoretical and experimental studies. Many of these questions still do not have definite answers. 

In polymer theory, infrared divergences are discussed as well the behaviour of the partition functions is analyzed at d < 4 and z oo. In other words, the dimension d proves to be marginal in polymer theory as well as in quantum electrodynamics and Landau-Ginzburg-Wilson s field theory. In particular, this explicitly manifests itself in the definition of z (see Kquation 9). 

The derivative -dAa h)/dh = is the force per unit cross-sectional area, also known as Derjaguin s disjoining pressure [4,5], Within the context of this definition, both Ao(/t) and W(fi) are positive in the case of a repulsion and negative in the case of an attraction. Molecular attraction forces prevail at long distances, while repulsive forces prevail at very short distances (the so-called Born repulsion). The principal theory that describes the interactions in a thin film is the well-known Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, which focuses on the analysis of the competitive contribution of molecular (dispersion) attractive forces and electrostatic repulsion to the interaction between surfaces separated by a liquid film. 

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