Gradient theory for structural forces in thin fluid films near the critical point.
We consider a general form of the local gradient theory for structural forces in thin fluid films near the critical point. A complete analytical solution of this problem at separation distances substantially larger than the molecular size is presented. That is, pi= -[330Psi(-4)H(8.8923-Psi) + 384exp(-Psi)H(Psi-8.8923)]H(-Gamma)+[1134.36Psi(-4)H(8.8923-Psi + 192exp(-Psi)H(Psi-8.8923)]H(Gamma) where Gamma <0 for similar (both attractive or both repulsive) and Gamma >0 for dissimilar (one attractive, another repulsive) bounding surfaces. Here pi and Psi are the structural force and the separation distance scaled in a certain way, and H(.) is a unit step function. For binary polymer films, the results are further elaborated to include a scaling dependence of the structural force on polymerization degrees of components.
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