Permittivity Gradient Theory

A mechanism involving spatial variation of the permittivity, e, has been suggested by Baldus and Zilker (2001). This model assumes that a spatial modulation of the refractive index, hence permittivity, is induced in the film. This is certainly reasonable, given the well-known photoorientation and birefringence gratings in azo systems. A force is then exerted between the optical electric field and the gradient in permittivity. Specifically, the force is proportional to the intensity of the electric field in the mass transport direction and to the gradient of the permittivity  

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If the correlation function of dielectric constcint (permittivity) h(r) is taken as the order parameter, Equation 7 is similar to Equation 2.3 129. It reveals Landau s mean field theory with a gradient term equivalent to Ornstein-Zernike s approximation (section 2.3). 

Some aspects that could be relevant have not yet been incorporated in the theory for the phase behaviour. A first issue is the effect of gradients in permittivity. Croze and Cates [88] demonstrated that even the depletion zones caused by neutral polymers are affected by charged surfaces. The electrical field present between like-charged surfaces polarize the neutral polymer chains because of their... 

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