Enhanced fluid flow through nanopores by polymer brushes.

Abstract

In the past few decades, much research has been devoted to nanoscale transport, despite its complexity. Here we present results, which are counterintuitive, showing that adsorption of the polystyrene-b-polyisoprene (PS-b-PI) diblock copolymer to the aluminum oxide nanopore membrane wall considerably reduces the friction of the organic solvents passing through the nanopore channels. The estimated apparent slip length for tetrahydrofuran (THF) liquid flow through 20 nm nanopore membranes increases from 0.13-0.16 μm for the bare nanopore to 3-13 μm after PS-b-PI polymer physisorbed to the pore surface to saturation. For the bare nanopore membranes, the slip length remains constant at different flow rates while after polymer adsorption it increases with the liquid flow shear rate. The shear rate dependence of the slip length is understandable from the point of view of polymer chains stretching dynamics under shear flow. The findings of this study may aid in understanding the physics of nannofluidics and have implications for biolubrication effects in biological systems.