Water, generally microscopic interactions

In the CHS model only nearest neighbors interact, and the interactions between amphiphiles in the simplest version of the model are neglected. In the case of the oil-water symmetry only two parameters characterize the interactions b is the strength of the water-water (oil-oil) interaction, and c describes the interaction between water (oil) and an amphiphile. The interaction between amphiphiles and ordinary molecules is proportional to a scalar product between the orientation of the amphiphile and the distance between the particles. In Ref. 15 the CHS model is generalized, and M orientations of amphiphiles uniformly distributed over the sphere are considered, with M oo. Every lattice site is occupied either by an oil, water, or surfactant particle in an orientation ujf, there are thus 2 + M microscopic states at every lattice site. The microscopic density of the state i is p.(r) = 1(0) if the site r is (is not) occupied by the state i. We denote the sum and the difference of microscopic oil and water densities by and 2 respectively and the density of surfactant at a point r and an orientation by p (r) = p r,U(). The microscopic densities assume the values = 1,0, = 1,0 and 2 = ill 0- In close-packing case the total density of surfactant ps(r) is related to by p = Ylf Pi = 1 - i i. The Hamiltonian of this model has the following form [15]... 

The relaxivity induced by gadolinium chelates due to inner-sphere water molecules, riIS, is well understood on the microscopic scale as can be seen from the above discussion. The contribution to the overall relaxation enhancement due to all other water molecules is normally summed up in the term r, generally called the outer-sphere contribution. The interaction between the water proton nuclear spin I and the gadolinium electron spin S is supposed to be a dipolar intermolecular interaction whose fluctuations are governed by random translational motion. The corresponding relaxation rate, l/Tly for unlike spins is given by Eq. (23) [88-90]... 

These variations between woods reflect differences in microscopic structure and chemical organization of the material, for phase geometry can be as important as molecular structure in determining the properties of both natural and synthetic multiphase systems (31). Therefore, it is clear that the mechanical behavior of the wood-water system cannot be explained entirely at the molecular level or as interaction of macromolecules with solvent. Nevertheless, the general trends observed do follow general principles of solvent-polymer interaction and can be so explained. 

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