Adsorption Kinetics of cis-1,4-Polyisoprene in Nanopores by In Situ Nanodielectric Spectroscopy

Using in situ nanodielectric spectroscopy, we studied the adsorption kinetics of cis-1,4-polyisoprene (PI) into porous alumina by following the evolution of the dielectrically active longest normal mode. We studied the influence of molar mass, nanopore diameter, and surface functionalization. Adsorption times depend strongly on the ratio 2Rg/D, where Rg is the radius is gyration and D is the pore diameter. For a given pore diameter, the characteristic adsorption times are some 8 orders of magnitude slower than the terminal relaxation times and more than 12 orders of magnitude slower than the segmental times. The extremely slow kinetics reflect the fact that exchanging chains with the pore surface have to pass through several unfavorable configurations (e.g., trains, loops). The molar mass dependence of the characteristic adsorption times (τads ∼ N2.6) is in good agreement with a scaling theory proposed by de Gennes and later refined by Semenov and Joanny. Subsequently, we investigated the imbibition of miscible PI blends by taking advantage of the difference in imbibition speeds of the respective homopolymers. We show that the shorter chains penetrate first the nanopores, whereas the longer chains enter only at the late stages of the filling process. Moreover, the long-time adsorption is dominated by an exchange mechanism involving primarily the shorter chains. The results from in situ nanodielectric spectroscopy demonstrate the capacity of the technique to provide the imbibition length, the adsorption kinetics, and, at the same time, the chain dynamics.