Imbibition and Adsorption of a Bottlebrush Polymer in Nanopores

Abstract

We report on the imbibition kinetics of bottlebrush polymer cis-1,4-polyfarnesene (PF) during flow in nanopores. To follow the polymer flow in situ, we employ in situ nanodielectric spectroscopy. The technique provides simultaneous access to the kinetics of imbibition and to the molecular dynamics during flow on the segmental and chain length scales. The imbibition process follows the t^1/2 dependence as predicted by the Lucas–Washburn equation. However, bottlebrush polymers with a molecular size smaller than the pore diameter (2R_g < d, d is the pore diameter) penetrate nanopores with a higher effective viscosity than in bulk. The adsorption time scales are much longer than any molecular process, being several orders of magnitude slower than the segmental and longest normal modes. Compared to linear polymers, bottlebrush polymers exhibit even slower adsorption with characteristic time scales having a weak molar mass (τ_ads ∼ N_bb^1.2±0.1, N_bb is the number of backbone repeat units), pore size (log(τ_ads) ∼ ξ/d, ξ = 20 nm), and temperature (E_act ∼ 16 ± 2 kJ/mol) dependence. These findings are discussed in terms of an increased number of contacts of the bottlebrush polymer with the surface. Lastly, we investigate the separation of a polymer blend with linear/bottlebrush topologies into its constituents by the difference in the imbibition kinetics.