Topology sorting: Separating linear/star polymer blend components by imbibition in nanopores

Abstract

We report the imbibition and adsorption kinetics of a series of symmetric linear/star cis-1,4-polyisoprene blends within the long channels of self-ordered nanoporous anodic aluminum oxide (abbreviated: AAO). Using in situ nanodielectric spectroscopy, we followed the evolution of the longest chain modes in the blends with a judicious selection of molar masses for the constituent components. We demonstrated differences in the imbibition kinetics of linear and star components based on the relative viscosities (e.g., polymers with lower zero-shear viscosity penetrated first the nanopores). Following the complete imbibition of the pores, the adsorption time, τads, of each component was evaluated from the reduction in the dielectric strength of the respective chain modes. In the majority of blends, both components exhibited slower adsorption kinetics with respect to the homopolymers. The only exception was the case of entangled stars mixed with shorter linear chains, the latter acting as a diluent for the star component. This gives rise to what is known as topology sorting, e.g., the separation of linear/star blend components in the absence of solvent. Moreover, a simple relation (τads ∼ 10 × tpeak; tpeak is the time needed for the complete filling of pores) was found for linear polymers and stars. This suggested that the characteristic timescale of imbibition (tpeak) governs the adsorption process of polymers. It further implied the possibility of predicting the adsorption times of high molar mass polymers of various architectures by the shorter imbibition times.