Lateral structures of thin films of ampholytic diblock copolymers adsorbed from dilute aqueous solution at the solid/liquid Interface

in Langmuir (1999), 15(20), 6984-6990

The lateral structures of dried thin films of the ampholytic diblock copolymer poly((methacrylic acid)-block-((dimethylamino)ethyl methacrylate)) adsorbed from dilute aqueous solution onto silicon ... [more ▼]

The lateral structures of dried thin films of the ampholytic diblock copolymer poly((methacrylic acid)-block-((dimethylamino)ethyl methacrylate)) adsorbed from dilute aqueous solution onto silicon substrates were investigated by scanning force microscopy (SFM) and diffuse X-ray scattering. The adsorbed amount of polymer, as a function of pH, reveals a maximum near the isoelectric point (IEP) of the polyampholyte. Different lateral structures are determined for samples adsorbed at pH values above the maximum of the adsorbed amount, as compared to the ones adsorbed at pH values below this maximum. At a pH around the IEP, the polyampholyte precipitates and the layers are formed by adsorption of flocks with sizes in the micrometer range. Lateral structures measured by SFM are similarly detected by diffuse X-ray scattering. The later technique delivers a statistical description of the lateral surface structures averaged over a larger area. The structures investigated are related to the polyampholyte structure in solution and can be explained 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. [less ▲]

Adsorption of ampholytic diblock copolymers from dilute aqueous solution at the solid/liquid interface

in Langmuir (1999), 15(4), 1260-1267

The adsorption of the ampholytic diblock copolymer poly(methacrylic acid)-block-poly((dimethylamino)ethyl methacrylate) (PMAA-b-PDMAEMA) and the corresponding homopolyelectrolytes of the two blocks, PMAA ... [more ▼]

The adsorption of the ampholytic diblock copolymer poly(methacrylic acid)-block-poly((dimethylamino)ethyl methacrylate) (PMAA-b-PDMAEMA) and the corresponding homopolyelectrolytes of the two blocks, PMAA and PDMAEMA, was investigated from dilute aqueous solution on silicon substrates. The adsorbed amount of polymer as a function of pH, polyampholyte concentration, and salt concentration in solution has been determined by ellipsometry at room temperature. As a function of pH the adsorbed amount reaches its maximum at the isoelectric point of the polyampholyte. Some adsorption takes place even in pH ranges where the surface charge has the same sign as the net charge of the polyampholyte. By variation of the polyampholyte concentration, typical adsorption isotherms were determined at several pH values. With increasing salt concentration the adsorbed amount increases, and above a critical concentration it diverges to very large values. The measured dependencies can be explained by the adsorption of one or the other of the two blocks depending on acidity and ionic strength and are in good agreement with theoretical predictions. Adsorption kinetics has also been studied in detail, and the diffusion coefficient of the polyampholyte toward the surface has been obtained in the early state of adsorption as a function of pH, polyampholyte concentration, and salt concentration. [less ▲]