The broken out and confinement phase separation structure evolution with the solution aggregation and relative crystallization degree in P3HT/N2200

Abstract

The phase separation structure evolution process, i.e. confinement and broke out phenomenon in crystallization/crystallization poly (3-hexylthiophene) (P3HT) and poly [[N,N-bis(2-octyldodecyl)-napthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]- alt-5, 5′-(2,2′-bithiophene)] (N2200) blends were controlled by the polymer solution aggregation behavior and relative crystallization degree of each component. In this study, two different molecular weight of P3HT, Mw = 6 kDa and Mw = 55 kDa were selected and blend with N2200 as the model systems. Different molecular weight of P3HT had different crystalline ability in blend films. A similar phase separation of both two polymer blends could form in good solvent chloroform (CF). Marginal solvents and thermal annealing were employed to change the polymer solution aggregation behavior and relative crystallization degree of the two components. On one hand, when p-xylene (pX) was added as the co-solvent to increase the aggregation of P3HT molecules, for P3HT (Mw = 6 kDa)/N2200, the P3HT phase broke the restriction of N2200 phase while there was almost unchanged in P3HT (Mw = 55 kDa)/N2200. On the other hand, during thermal annealing, the P3HT molecule had a stronger molecular moving ability in P3HT (Mw = 6 kDa)/N2200 than that in P3HT (Mw = 55 kDa)/N2200 (the relative crystallization degree of these two polymers in P3HT (Mw = 6 kDa)/N2200 and P3HT (Mw = 55 kDa)/N2200 are 142 and 3, respectively). The pristine phase separation of P3HT (Mw = 6 kDa)/N2200 was destroyed effectively due to the unmatched crystallization degree of the two components and large sized fibrous phase separation was formed during thermal annealing. However, the pristine phase separation was almost unchanged in P3HT (Mw = 55 kDa)/N2200, and the P3HT molecule could partly ordered arrangement, which probably come from the almost matched crystallization degree of these two polymers. The results indicate that it is the Gibbs free energy that controls the phase separation in different relative crystallization degree. And different chain entanglements behavior was likely to be the main source of the morphological stability.