The critical behavior of three equimolar deuterated polybutadiene/ polystyrene (d-PBPS) blends was measured by small-angle neutron scattering. The three blends differ by the content of the 1,4 and 1,2 units of the d-PB component. It was found that the Ginzburg number increases with 1,2 unit content which even leads to a crossover like the "Fisher renormalized" critical behavior. The larger content of 1,2 units is supposed to increase the free volume change upon mixing which influences the Ginzburg number. Thus the nonuniversality of the Ginzburg number is clearly demonstrated.
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