Highly regular polyampholytic structures adsorbed directly from solution

This article concerns the adsorption of the diblock polyampholyte poly(methacrylic acid)-block-poly((dimethylamino)ethyl methary-late) (PMAA-b-PDMAEMA) from aqueous solution on silicon substrates. The investigated polyampholyte is characterized by a small molecular weight around 15,000 g/mol and a big positively charged PDMAEMA block. The adsorbed amount determined by ellipsom-etry was str ongly influenced by the pH of the adsorption solution. Using dynamic light scattering polyampholytic structures with diameters around 50 nm were found in aqueous solution. The hy-drodynamic diameter was hardly affected by changing the pH of the polymer solution. Analogous regular structures were also found by scanning force microscopy (SFM) and grazing incidence, small angle X-ray scattering (GISAXS) at the silicon surface after the adsorption process. While SFM provides a topographical image of a small part of the adsorbed polyampholytic layer; GISAXS was used to get a statistical description of the lateral surface structures. The adsorbed structures were highly regular and their sizes were nearly pH independent over a lar ge pH region. Only directly at the isoelectric point of the polyampholyte larger adsorbed structures were observed. Compared with earlier investigated PMAA-b-PDMAEMA systems we are now able to prepare highly regular polyampholytic structures at silicon surfaces. There are two kinds of interactions for the adsorbed micelles. First, the charged block of the chains is directly attracted to the substrate via electrostatic interactions, while the uncharged part of the chains is only hydrophobically attracted via the hydrophobic core of the adsorbed micelle.