(578c) Dielectric Relaxation of Tethered Polyisoprene in Nanoscale

Most studies about relaxation of tethered polymers have been performed on the systems where polymers are attached to a platelet structure or adsorbed onto a surface of other geometries. This talk presents the relaxation dynamics of polymers which are confined in nanoscale by tethering to spherical nanoparticles. In our system, all polymer chains are grafted to nanoparticles and as-synthesized materials are well dispersed and suspended without any additional solvents. Therefore, understanding of nanoscale dynamics of polymer in the system is straightforward from bulk measurement.

In this study, synthesized cis 1-4 Polyisoprene (PI) is tethered to the surface of silica nanoparticles, and dielectric relaxation behavior is probed by broadband dielectric spectrometer. Global chain relaxation is conveniently explored since the net dipole moment of an entire chain of cis 1-4 PI is parallel to the end to end vector of the repeating unit, which is the characteristics of type A dielectric polymers. Segmental mode relaxation provides the information about the local relaxation from the components perpendicular to the chain backbones. The effects of grafting densities and molecular weights in the spectrum from unentangled to highly entangled regime have been studied. For example, when PI molecular weight is in unentangled range, we observe that global chain relaxation time ~ 1.65 E-01 s of tethered 3K PI is ~10^5 times slower than the relaxation time ~ 2.27 E-06 s of untethered 3K PI at 20 °C, indicative of highly entangled polymer dynamics for tethered 3K PI. Segmental mode relaxation time also becomes ~10^3 times longer when 3K polymers are tethered.  We propose the model to understand the effect of molecular weight and grafting density on global chain and local relaxation when all polymers are attached to nanoscale spherical particles.