Flory $\chi $ of the homologous series of deuterated polystyrene-b-poly(n-alkyl methacrylates): small angle neutron scattering and theoretical studies

We have performed small angle neutron scattering and theoretical studies of the homologous series of deuterated polystyrene-b-poly(n-alkyl methacrylates) from methyl to n-hexyl groups that cover from UODT (upper order-disorder transition) to LODT (lower DOT), and barotropic to baroplastic behavior.~ It was shown that the effective Flory $\chi $ from the measurements reveal a monotonic dependence on 1/T for UODT (methyl, n-hexyl) systems and a complicated dependence for LDOT (ethyl to n-pentyl) systems. The recently developed compressible random-phase approximation (RPA) analysis has been applied to the copolymers to interpret in a unified way such diversified temperature and pressure dependence of $\chi $ and the transitions. Specific interactions (SI) and compressibility were incorporated through the RPA interaction fields in this theoretical approach. It was argued that the SI gives a major contribution to the LDOT behavior and the complicated dependence of $\chi $ on 1/T. The compelling changes in $\chi $ and the pressure responses of transitions according to the pendant group size were also interpreted successfully with the theory.