Preparation of Oriented PS-b-PEO Block Copolymer Membranes by Air-flow Method

A new and facile air-flow method was employed to prepare block copolymer membranes with different morphology. PS-b-PEO block copolymers were synthesized by atom transfer radical polymerization (ATRP). The molecular characteristics of the block copolymers were confirmed by H-1-NMR, FTIR spectroscopy and gel permeation chromatography (GPC). AFM and SEM were employed to characterize the surface morphology and inner structure of the films. Effects of molecular structure, air-flow velocity, air-flow temperature and substrate affinity on the membrane surface morphology and internal structure were studied. Vertically oriented microphase structure on the top surface of the membrane can be achieved when the PS mass fraction was between 83% and 85%, air-flow temperature was 50 degrees C and air-flow velocity was 4 m/s. When the liquid film was treated with an air speed outside the range of 3 similar to 5 m/s, no regular structure was observed. Similarly,when the air-flow temperature was too high or too low, no regular structure was observed. Substrates with different contact angles were prepared by chemical modification. Results showed that when the films were prepared on silicon substrates with contact angle less than 90 degrees under appropriate air-flow condition, vertical orientation of cylinder nanochannels formed only in the regions at the top and bottom layers of the block copolymer films while irregular structure appeared in the middle part.