SYNCHROTRON SAXS STUDY OF THE MICROPHASE SEPARATION TRANSITION IN DIBLOCK COPOLYMERS

The microphase separation transition (MST) in a nearly symmetric diblock copolymer is studied using time-resolved synchrotron SAXS. The transitions from the lamellar microphase to the isotropic melt and vice versa appear in the form of pronounced singularities in height and width of the main scattering maximum as a function of the temperature. The plot of the reciprocal scattering maximum S-1(q*) vs the reciprocal absolute temperature T-1 can be fitted to the corresponding theoretical function in the Hartree approximation although the present degree of polymerization N is much lower than the usually given limit of N > 10(4). The observed scattering functions fit well to the theoretical Leibler-type structure factors, modified to take polydispersity into account. The evaluation of the experimental data yields several parameters of interest to be compared with their theoretical predictions. The observed temperature dependence of the peak position q* is discussed in relation to a temperature-dependent radius of gyration R(G) and a temperature-dependent dependent x*. A computational error present in a previous paper is corrected in the Appendix.