Abstract
Summary: The size, aggregation number and other quantities which characterize the formation of micelles in a bidisperse solution of block copolymers which are chemically identical but have different block asymmetries has been studied in a selective solvent using LS and SANS techniques. Experimental results for the comicellization of two chemically identical block copolymers (high molecular weight, PS‐PI, and a low molecular weight dPS‐PI with a deuterated PS block) and two slightly incompatible copolymers (high molecular weight PS‐HPI, and dPS‐PI) in decane, a selective solvent for PI, are reported. Individually, each of the PS‐HPI and PS‐PI copolymers formed micelles with a PS core, which were stable over the entire temperature range covered by the experiments (25–70 °C). The small copolymer, dPS‐PI, formed micelles with a highly swollen core at low temperatures and was molecularly dispersed above the critical micelle temperature (47 °C). Comicellization was observed for both pairs of copolymers studied over a broad range of mixing ratios. The mixed micelles were comprised of large copolymer (PS‐HPI or PS‐PI) and a portion of the small copolymer (dPS‐PI). The amount of adsorbed dPS‐PI copolymer increased with increasing weight fraction of this copolymer and decreased with increasing temperature. The critical comicellization temperature was estimated as 70 and 60 °C for the comicelles based on PS‐HPI and PS‐PI copolymers, respectively. The SANS data suggest that the small copolymer does not form a shell coating the PS core of the initial micelle, but is instead incorporated into the core where it forms a layer of mixed dPS and PS chains.
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