With most blends of chemically different polymers, thermodynamic immiscibility makes the details of their phase separation an important field of inquiry for both science and industry. However, controlling and designing such phase separation dynamics remain difficult given the limited understanding of the physics involved.

To help bridge this knowledge gap, Sato et al. examined the phase separation process of an unentangled polymer blend. Polyisoprene (PI) has a dipole alignment that makes its global motion activate a slow dielectric relaxation, while poly(4-ethylstyrene) (PC2St), which does not feature such dipoles, is dielectrically inert. Additionally, because PC2St is much less mobile than PI at a similar molecular weight, the blend’s slow mechanical relaxation mainly reflects the PC2St motion.

“The blend’s unique features allowed us to evaluate the friction coefficients of both components separately from the dielectric and mechanical data of the blend at high temperatures, when it was in the uniform one-phase state and the well-established Rouse model was applicable to those data,” said author Hiroshi Watanabe.

The researchers then extrapolated the data to the low temperatures where phase separation occurs, applied the extrapolated data to a standard time-dependent equation describing phase separation dynamics, and conducted a simulation for the blend that reproduced characteristic features of experimentally observed phase separation.

“This work shows the importance of the time- and composition-dependent changes of the frictions of the components, especially of the slow component, in the phase separation in actual blends,” said Watanabe. “In the future, we would like to apply our methodology to investigate flow effects on the structure and properties, which would further our understanding of phase separation dynamics.”

Source: “Experimental study of phase separation in dynamically asymmetric unentangled polymer blend,” by Takeshi Sato, Yumi Matsumiya, and Hiroshi Watanabe, Journal of Chemical Physics (2022). The article can be accessed at https://doi.org/10.1063/5.0124087.