Nanoscale viscosity of confined polyethylene oxide
Zhang, Z.; Ding, J.; Ocko, B.M.; Fluerasu, A.; Wiegart, L.; Zhang, Y.; Kobrak, M.; Tian, Y.; Zhang, H.; Lhermitte, J.; Choi, C.-H.; Fisher, F.T.; Yager, K.G.; Black, C.T. "Nanoscale viscosity of confined polyethylene oxide" Physical Review E 2019
We use XPCS to probe the nanoscale viscosity of nanoparticles dispersed in polymer and confined within nano-channels.
Complex fluids near interfaces or confined within nanoscale volumes can exhibit substantial shifts in physical properties compared to bulk, including glass transition temperature, phase separation, and crystallization. Because studies of these effects typically use thin film samples with one dimension of confinement, it is generally unclear how more extreme spatial confinement may influence these properties. In this work, we used x-ray photon correlation spectroscopy and gold nanoprobes to characterize polyethylene oxide confined by nanostructured gratings (<100nm width) and measured the viscosity in this nanoconfinement regime to be ~500 times the bulk viscosity. This enhanced viscosity occurs even when the scale of confinement is several times the polymer's radius of gyration, consistent with previous reports of polymer viscosity near flat interfaces.