Temperature-Responsive Nanoporous Membranes from Self-Assembly of Poly(N-isopropylacrylamide) Hairy Nanoparticles

Nanoporous membranes play a critical role in numerousseparationson laboratory and industrial scales, ranging from water treatmentto biotechnology. However, few strategies exist that allow for thepreparation of mechanically robust nanoporous membranes whose separationproperties can be easily tuned. Here, we introduce a new family oftunable nanoporous membranes based on nanoparticles decorated withtemperature-responsive polymer brushes. We prepared mechanically robustmembranes from hairy nanoparticles (HNPs) carrying PNIPAM polymerbrushes. We assembled the HNPs into thin films through pressure-drivendeposition of nanoparticle suspensions and measured the permeabilityand filtration cutoff of these membranes at different temperatures.The membrane pore diameter at room temperature varied between 10 and30 nm depending on the polymer length. The water permeability of thesemembranes could be controlled by temperature, with the effective porediameter increasing by a factor of 3-6 (up to 100 nm) whenthe temperature was increased to 60 degrees C. The size selectivityof these membranes in the filtration of nanoparticles could also beattenuated by temperature. Molecular dynamics computer simulationsof a coarse-grained HNP model show that temperature-sensitive poressizes are consistent with our experimental results and reveal thepolymer configurations responsible for the observed filtration membranepermeability. We expect that these membranes will be useful for separationsand in the preparation of responsive microfluidic devices.