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−polymer 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 blend 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 readily analyzed as a result of the finite drop size. Intermediate time data are compared to the predictions of diffusion-limited segregation models proposed by Budkowski, Losch, and Klein (BLK) and by Semenov that have been modified to treat interfacial tension data. The apparent block copolymer diffusion coefficients obtained from the two analyses fall in the range of 10-5−10-6 cm2/s, in agreement with the estimated self-diffusion coefficient of the PDMS homopolymer matrix.