Adsorption behavior of polystyrene-polyisoprene diblock copolymers with zwitterionic groups using quartz crystal microbalance: Effect of different microstructures

The adsorption behavior of poly(styrene-b-isoprene) (PS-b-PI) copolymers functionalized with polar sulfobetaine zwitterionic groups at different positions along the backbone was investigated. Using dilute solutions in toluene, adsorption onto gold surface was investigated using a quartz crystal microbalance (QCM). ZwIS and ZwSI, ZwISZw, and SZwI are PS-b-PI copolymers functionalized at the alpha-position (zwitterionic group is attached to isoprene or styrene), at the alpha,omega-positions, and at the junction-point in the chain, respectively. The copolymers showed interesting adsorption behavior according to the zwitterion position. The adsorption isotherms for the copolymers exhibited typical Langmuir isotherm behavior. They showed different adsorbing amounts, which was explained by possible conformational states of copolymers on the surface. It was found that the position of zwitterionic groups has a major role on adsorption kinetics despite similar molecular weight and composition for the copolymers.