The behavior of polymer chains moving inside porous materials is important for many applications, ranging from gel permeation chromatography, filtration, heterogeneous catalysis, oil recovery etc. When a polymer melt gets into contact with the opening of a narrow pore the capillary force is strong and drags the chains into the pore. Herein we employ a new nanofluidic approach and explore the imbibition kinetics and, simultaneously, the polymer segmental dynamics. The polymer is poly(n-butyl methacrylate) (PnBMA), the confining medium is nanoporous alumina and the technique is in situ dielectric spectroscopy at temperatures in the range 30-50 K above the glass temperature. A model provides the imbibition length from the measured dielectric strength of the segmental process. The relaxation times of the segmental process during imbibition are isochronal except at early stages where a speed-up is observed. Furthermore, as polymer segments flow inside the pores the distribution of relaxation times remain constant (Havriliak-Negami shape parameters similar to the bulk). Imbibition at longer length scales associates with the effective viscosity of the chains and provides a stringent test of the Lucas-Washburn equation applicable to Newtonian liquids. The equation fails to describe the imbibition process because the prefactor to the t1/2 (t; time) dependence does not adequately describe the process. Imbibition of polymer blends composed of long and short chains reveal the enrichment of the pores by the shorter chains by their faster imbibition with possible application in fractionation.

In situ monitoring the imbibition of poly(n-butyl methacrylates) in nanoporous alumina by nanodielectric spectroscopy

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.