Scattered intensity by a cross-linked polymer blend

Cross‐linked mixtures of polystyrene and poly(vinyl methyl ether) exhibit a non‐vanishing zero‐angle intensity in small‐angle neutron scattering experiments. A possible explanation is that fluctuations in composition in the mixture may be frozen by the presence of cross‐links. Assuming this, we introduce a screening length κ by the condition that the scattered intensity should not be changed by cross‐linking. We find κ2 ∼ C/(χ − χi), where C is an elastic constant, χ and χi, respectively, the inverse temperature and that where cross‐linking is performed. When the temperature is varied, we find three regimes. In the first one, the scattered intensity is monotonously decreasing. In the second one, it has a finite maximum. In the last one, the maximum eventually diverges.