Concentration fluctuation in a polymer mixture

The critical behavior in a mixture of polystyrene and polymethylphenylsiloxane has been examined by the angular distribution of the scattered light intensity over 5.7<k<19.6 μ${\mathrm{m}}^{\mathrm{-}1}$ and 0.045<T-${\mathit{T}}_{\mathit{c}}$<2.4 °C, where k is the scattering wave number and ${\mathit{T}}_{\mathit{c}}$ is the critical mixing temperature. The osmotic compressibility obeys a relation ${\mathrm{\chi }}_{\mathit{T}}$∼(T-${\mathit{T}}_{\mathit{c}}$ ${)}^{\mathrm{-}\gamma }$ with γ=1.22±0.02 and the long-range correlation length ξ∼(T-${\mathit{T}}_{\mathit{c}}$ ${)}^{\mathrm{-}\nu }$ with ν=0.62±0.02, in good agreement with the three-dimensional Ising-model universality.