Self-Seeding Procedure For Obtaining Stacked Block Copolymer Lamellar Crystals In Solution

We examined the formation of self-seeded platelet-like crystals from polystyrene-block-polyethylene oxide (PS-b-PEO) diblock copolymers in toluene as a function of polymer concentration (c), crystallization temperature (T-C), and self-seeding temperature (T-SS). We showed that the number (N) of platelet-like crystals and their mean lateral size (L) can be controlled through a self-seeding procedure. As (homogeneous) nucleation was circumvented by the self-seeding procedure, N did not depend on T-C. N increased linearly with c and decayed exponentially with TSS but was not affected significantly by the time the sample was kept at TSS. The solubility limit of PS-b-PEO in toluene (c*), which was derived from the linear extrapolation of Nc -> 0 and from the total deposited mass of the platelets per area (MCc -> 0), depended on TC. We have also demonstrated that at low N, stacks consisting of a (large) number (eta) of uniquely oriented lamellae can be achieved. At a given T-C, L was controlled by N and eta as well as by increment Delta c = c - c*. Thus, besides being able to predict size and number of platelet-like crystals, the self-seeding procedure also allowed control of the number of stacked lamellae in these crystals.