Microphase separation of crosslinked polymer blends in solution

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Abstract
We consider here a polymer blend made of two crosslinked polymers A and B of different chemical nature, in the presence of a common solvent assumed to be good for both species. To study the solvent effects on the microphase separation of the mixture, we first apply the so-called blob model which is a direct consequence of the renormalization theory. In this model and at large scales compared with the screening length ξ of the semidilute regime, polymer chains A and B are viewed as sequences having blobs of size ξ as subunits. Within this model, we calculate the structure factor enabling us to derive all microphase critical properties. The main result is that, the swelling effects simply lead to a renormalization of these properties, and that the renormalization factors are powers of the monomer concentration. Quantitatively, such a renormalization is in agreement with the fact that, in presence of a good solvent, the mixture is more compatible. The blobs picture is a mean-field approximation, to go beyond this approach which neglects the strong fluctuations of the density near the critical point, we reconsider the problem using the renormalization-group techniques. We show that these strong fluctuations lead to a microphase critical behavior characterized by nonclassical exponents, which are found to be identical to those of the Ising-type system.