Critical Neutron Scattering in a Polymer Blend above and below the Critical Point of Demixing: Critical Exponents and Amplitude Ratios

The critical behavior of a polymer blend was measured by small-angle neutron scattering above and below the critical temperature ${T}_{c}$, i.e., outside and inside the unstable region. The critical exponents and the amplitudes of the susceptibility and the correlation length were determined. For $T>{T}_{c}$ the critical exponents $\ensuremath{\gamma}$ and $\ensuremath{\nu}$ are consistent with the renormalization-group predictions. Below ${T}_{c}$, however, deviations from the expected values were observed. Also experimental critical amplitude ratios (20-30)% smaller than predicted were found.