Insights into polymer mixing behaviour from neutron scattering experiments and a simple thermodynamic theory

Small angle neutron scattering provides directly values of the second derivative of the free energy of mixing in polymer blends via the scattered intensity extrapolated to zero angle. The literature contains much valuable SANS data from polymer mixtures, and we have been revisiting some of it, including our own data. The Dartmouth group has developed an approach to polymer miscibility using a locally correlated lattice model for the equation of state, and we have demonstrated that this not only describes well the experimental SANS data on polymer mixtures but allows new insights into the behaviour of both polymers and their mixtures. The characteristic parameters obtained by fitting the data have been successfully shown to be transferable from one data set to another, to be able to correctly predict behaviour outside the experimental range of the original data and to allow meaningful comparisons to be made between different polymer mixtures.