Highly regular polyampholytic structures adsorbed directly from solution

This article concerns the adsorption of the diblock polyampholyte poly(meth acrylic acid)-block-poly((dimethylamino)ethyl metharylate) (PMAA-b-PDMAEMA) from aqueous solution on silicon substrates. The investigated polyampholyt e is characterized by a small molecular weight around 15,000 g/mol and a bi g positively charged PDMAEMA block. The adsorbed amount determined by ellip sometry was strongly influenced by the pH of the adsorption solution. Using dynamic light scattering polyampholytic structures with diameters around 5 0 nm were found in aqueous solution. The hydrodynamic diameter was hardly a ffected by changing the pH of the polymer solution. Analogous regular struc tures were also found by scanning force microscopy (SFM) and grazing incide nce, small angle X-ray scattering (GISAXS) at the silicon surface after the adsorption process. While SFM provides a topographical image of a small pa rt of the adsorbed polyampholytic layer, GISAXS was used to get a statistic al description of the lateral surface structures. The adsorbed structures w ere highly regular and their sizes were nearly pH independent over a large pH region. Only directly at the isoelectric point of the polyampholyte larg er adsorbed structures were observed. Compared with earlier investigated PM AA-b-PDMAEMA systems we are now able to prepare highly regular polyampholyt ic structures at silicon surfaces. There are two kinds of interactions for the adsorbed micelles. First, the charged block of the chains is directly a ttracted to the substrate via electrostatic interactions, while the uncharg ed part of the chains is only hydrophobically attracted via the hydrophobic core of the adsorbed micelle. (C) 2001 Academic Press.