Lateral structures of thin films of ampholytic diblock copolymers adsorbedfrom dilute aqueous solution at the solid/liquid interface

The lateral structures of dried thin films of the ampholytic diblock copoly mer poly((methacrylic acid)-block-((dimethylamino)ethyl methacrylate)) adso rbed from dilute-aqueous solution onto silicon substrates were investigated by scanning force microscopy (SFM) and diffuse X-ray scattering. The adsor bed amount of polymer, as a function of pH, reveals a maximum near the isoe lectric point (IEP) of the polyampholyte. Different lateral structures are determined for samples adsorbed at pH values above the maximum of the adsor bed amount, as compared to the ones adsorbed at pH values below this maximu m. At a pH around the IEP, the polyampholyte precipitates and the layers ar e formed by adsorption of flocks with sizes in the micrometer range. Latera l structures measured by SFM are similarly detected by diffuse X-ray scatte ring. The later technique delivers a statistical description of the lateral surface structures averaged over a larger area. The structures investigate d are related to the polyampholyte structure in solution and can be explain ed by the interplay of the electrostatic interactions of the two oppositely charged blocks of the polyampholyte and the charged surface, as well as by the dependencies of charge densities on pH.