Preparation Of Oriented Block Copolymer Membranes By Air-flow Method

Block copolymers self-assembled into regular nanostructures with a periodic of10nm to100nm have been the subject of intense interest from both the academic andindustrial communities. The regular morphologies have shown potential applicationsin microelectronics, selective separation and fuel cell membranes. A simple and facilemethod for preparing block copolymer membrane with controllable microphasestructure remains a major challenge. In this thesis, we synthesized PS-b-PEO andPS-b-PMMA by atom transfer radical polymerization (ATRP). A simple and facilemethod for preparing copolymer membranes was described. The details are asfollows:(1) PS-b-PEO block copolymers with three different kinds of molecular weightwere synthesized by ATRP and their molecular characteristics were confirmed by1HNMR, FT-IR spectroscopy and gel permeation chromatography (GPC). Effects ofmolecular structure, water content in the mixed solvent, polymer concentration,air-flow temperature, air-flow velocity and substrate affinity on the membrane surfacemorphology and internal structure were studied. Substrates with different contactangles were prepared by chemical modification. AFM and SEM were employed tocharacterize the surface morphology and inner structure of the films.Asymmetric-structured membranes with vertically oriented structure on the top andbottom surface and irregular structure in the bulk could be prepared under appropriateair-flow condition on silicon substrates with contact angles less than90°. Thisasymmetric structure showed effectiveness in the separation of VO2+/H+.(2) PS-b-P4VP block copolymer membranes were prepared by air-flow method.The center-to center distance between the cylindrical domains were controlled bychanging the concentration of polymer solutions. As the concentration increased from 0.5wt%to4wt%, the center-to-center distance increased from25nm to29nm whilethe pore diameter increased from12nm to15nm. When the films were annealed inthe THF vapor, hexgonally packed cylindrical domains were achieved. SEM andGISAXS were employed to characterized the internal structure of the films. Weobtained a structure with a vertical orientation of cylindrical nanostructure locatednear the skin layer of the BCP films, while the part beneath the skin layer exhibited anirregular orientation of cylindrical nanostructure. This kind of structure was verystable even after19h of solvent-annealing treatment and has potential applications inthe selective separation of proteins or nanoparticles.