Component Dynamics in Polystyrene/4‐Pentyl‐4′‐Cyanobiphenyl Blend

We studied the dielectric and viscoelastic relaxation behaviors of polystyrene (PS)/4‐pentyl‐4′‐cyanobiphenyl (5CB) miscible blend, and examined the relationship between segmental motion of PS and rotational motion of 5CB in the blend. Viscoelastic measurements could detect the global motion of PS‐chain, and the longest relaxation time $τL$ of PS was determined. On the other hand, 5CB motion was detected by dielectric measurement, because of much larger electric dipole of cyano group in 5CB than that of PS. The dielectric spectra of the blends were bimodal, indicating the existence of two distinct dynamical modes related to the 5CB motion. The relaxation times of these two modes are named $τslow$ and $τfast.$ Temperature dependences of $τslow$ and $τL$ were found to be almost the same, and $τslow$ was close to the segmental relaxation time $τseg$ of PS estimated from the $τL$ values. This means that these two motions, PS‐segmental motion and slow mode of 5CB are cooperative. On the other hand, temperature dependence of $τfast$ was weaker than those of $τL$ and $τslow,$ suggesting that the fast mode of 5CB is not cooperative with PS‐chain motion.