Diblock polyampholytes at the silicon/water interface: adsorption at various modified silicon substrates

The adsorption behaviour of the ampholytic diblock copolymer poly(methacrylic acid)-block-poly((dimethylamino)ethyl methacrylate), PMAA-b-PDMAEMA, was investigated on differently prepared silicon surfaces. All adsorption experiments were performed from aqueous solutions as a function of pH. The polyampholyte amount adsorbed was determined ellipsometrically, while the topographies of the adsorbed polymer were investigated using scanning force microscopy (SFM). Three polyampholyte systems with similar molecular weight around 60000 g mol–1 and different block ratios were adsorbed on three different types of silicon substrates. Depending on the pretreatment the silicon substrates contained different isoelectric points (IEP) and hydrophobicity. The adsorbed amount, as a function of pH, was characterized by maxima and minima near the IEP of the polyampholytes. In the case of polyampholytes containing an IEP close to the IEP of the silicon substrates, the nature of the substrate strongly influenced the adsorption behaviour. Even a complete erasure of one adsorption maximum could be observed in some cases. In contrast to this, polyampholytes with an IEP in a pH area far away from the IEP of the substrates adsorbed in a quite similar manner on the different substrates.