pH-responsive behavior of selectively quaternized diblock copolymers adsorbed at the silica/aqueous solution interface

The desorption and subsequent pti-responsive behavior of selectively quaternized poly(2-(dimethylarnino)ethyl methacrylate)-block-poly(2(diethylamino)ethyl methacrylate) (PDMA-PDEA) films at the silica/aqueous solution interface has been characterized. The copolymer films were prepared at pH 9, where micelle-like Surface aggregates are spontaneously formed on silica. The subsequent rinse with a copolymerfree electrolyte solution adjusted to pH 9 causes partial desorption of the weakly or non-qUaternized copolymers, but negligible desorption for the highly qUaternized copolymers. Further rinsing with a pH 4 electrolyte solution results in additional desorption and extension (swelling) of the remaining adsorbed copolymer film normal to the interface. This pH-responsive behavior is reversible for two pH cycles (9-4-9-4) as monitored by both quartz crystal microbalance with dissipation monitoring (QCM-D) and also zeta potential measurements. The magnitude of the pH-responsive behavior depends on the mean degree of quaternization of the PDMA block. Moreover, a combination of contact angle data, zeta potential measurements and in situ atomic force microscopy (AFM) studies indicates that the pH-responsive behavior is influenced not only by the number of cationic binding sites oil the adsorbed copolymer chains but also by the adsorbed layer structure. (c) 2007 Elsevier Inc. All rialus reserved.