Segregation dynamics of block copolymers to immiscible polymer blend interfaces

We report the first application of dynamic interfacial tension measurements to characterize segregation rates of diblock copolymers to a polymer-polym er interface. The system investigated is a poly(styrene-b-dimethylsiloxane) [P(S-b-DMS); M-n = 13 000] symmetric diblock copolymer added to a molten b lend of the corresponding immiscible homopolymers. Interfacial tensions are measured by the pendant drop technique with poly(styrene) [PS; M-n = 4000] as the pendant drop phase and a mixture of poly(dimethylsiloxane) [PDMS; M -n = 1600] with silane-terminated P(S-b-DMS) as the surrounding phase. The pendant drop technique is found to suffer from two intrinsic limitations in this application: short time data are inaccessible due to the finite time required for the drop shape to equilibrate, and long time data may not be r eadily analyzed as a result of the finite drop size. Intermediate time data are compared to the predictions of diffusion-limited segregation models pr oposed by Budkowski, Losch, and Klein (BLK) and by Semenov that have been m odified to treat interfacial tension data. The apparent block copolymer dif fusion coefficients obtained from the two analyses fall in the range of 10( -5)-10(-6) cm(2)/s, in agreement with the estimated self-diffusion coeffici ent of the PDMS homopolymer matrix.