Salt Concentration Dependence of Swelling States for Poly(sulfobetaine) Brush at Aqueous Solution Interface

Swelling states of poly(3-(N-2-methacryloyloxyethyl-N,N-dimethyl) ammonatopropanesulfonate) (MAPS) brush in aqueous solutions were investigated by atomic force microscopy (AFM) and neutron reflectivity measurement. The thickness of swollen poly(MAPS) brush evaluated by AFM was increased from 61 to 87 nm with an increase in NaCl concentration from 0 to 0.05 M, and was dramatically increased up to 153 nm at 0.5 M NaCl aqueous solution. At low salt concentration, poly(MAPS) brush chains formed shrunk structure due to the inter- and intrachain attractive electrostatic interactions, while the brush chains stretched up with increasing salt concentration due to the screening effect by hydrated salt ions.