In Situ Monitoring Polymer Imbibition in Nanopores by Nanodielectric Spectroscopy

The question of how polymers penetrate narrow pores (2D confinement) is relevant in several applications (e.g. inkjet printing). In this study, the construction of a nanofluidic method capable of following the details of polymer imbibition in situ is explored. The method provides simultaneous access to the kinetics of imbibition, the molecular dynamics and the viscosity experienced by the polymer during flow. Two particular systems have been investigated. One is based on the highly polar poly(n-butyl methacrylate) (PnBMA) and the other on the relatively apolar cis-1,4-polyisoprene (PI). The former (PnBMA) provided information of the segmental dynamics and of the imbibition length during flow facilitating a stringent test of the Lucas-Washburn equation applicable to Newtonian fluids. With respect to PI, results showed that polymer imbibition proceeds in two time-regimes with higher effective viscosity than in bulk. In a recent publication [C.-H. Tu et al. Phys. Rev. Lett. 125, 127802, 2020] we discussed this finding with the help of a microscopic picture that considers the competition from an increasing number of chains entering the pores and a decreasing number of fluctuating chains with time. The latter provided unambiguous evidence for increasing adsorption sites during flow.