For a well-entangled polyisoprene (PI; molecular weight = 260k) equilibrated under pressurized carbon dioxide (CO
2) at 25 °C, linear viscoelastic and dielectric data, respectively, were measured with a stress-controlled rheometer and a dielectric bridge being equipped with respective high-pressure cells. The viscoelastic and dielectric data shifted to higher frequencies with increasing CO
2 pressure, indicating that the pressurized CO
2 dissolved into PI thereby accelerating the global motion of PI. For those data at various CO
2 pressure, time-CO
2 pressure superposition held well and a single master curve was obtained, and the horizontal/vertical shift factors were consistent for the viscoelastic and dielectric data. These results indicated that the dissolved CO
2 behaved just as an ordinal solvent to accelerate the global motion of PI as in ordinary solutions. In fact, the dynamic tube dilation (DTD) relationship between the viscoelastic and dielectric data, known to be valid for ordinary solutions/bulk of linear PI, was found to work also the PI/CO
2 system, which confirmed the simple solvent role of the pressurized CO
2 for the global motion of PI. Thus, the knowledge for ordinary polymer solutions would work for processing of polymer/CO
2 systems.
View full abstract