Solute- and Temperature-responsive Smart Membranes Formed by Covalent Layer-by-layer Assembly
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abstract
Surfaces with Hofmeister-like anion-responsive wettability were prepared by covalent layer-by-layer assembly of PNIPAM-c-PNASI with 10 and 100 nm diameter aminated silica nanoparticles on Si surfaces. Their morphologies and surface roughness were investigated in a step-wise fashion by tapping mode AFM. The roughness of the polymer nanocomposite surface was found to increase when the nanoparticles were functionalized to the substrate. Significant aggregation of the nanoparticles occurred in the process of assembling multiple layers of the copolymer and nanoparticles on the substrate. The change in surface roughness increased the contact angle of 1.2 M Na2SO4 solution on the surface by 40 compared to pure water. Aggregation of the polymer/nanoparticles composites plays a major role in the enlargement of the surface roughness, which leads to changes in the surface wettability. These films also show variations in the Young's modulus induced by external stimuli, where temperature variation and counter ion addition to the surrounding solution were both studied to investigate their effect, as determined by colloidal probe force microscopy. Here, the elastic modulus was found to be in the range of 3 MPa to 189 MPa; dependent on the exposure of the polymer composite to various temperatures, counter ions and rinsing procedures.
