Adsorption/Desorption Behavior of Charged Polymer Nanoparticles on a Mineral Surface in an Aqueous Environment

Abstract

The adsorption and desorption behavior of anionic and cationic spherical polyelectrolyte brushes (SPB) on mica surfaces in an aqueous medium is discussed. The SPB consist of a polystyrene core with diameters of 136 nm (anionic SPB) and 90 nm (cationic SPB), respectively, on to which linear polyelectrolyte chains are affixed by a grafting-from technique. Negatively charged particles consist of polystyrene–sulfonate chains and positively charged SPB consist of cationic polyelectrolyte chains (poly((2-acryloxy)ethyl)-trimethylammonium-chloride). The SPB are extensively characterized in aqueous dispersion whereas their interaction with mica surfaces is investigated by atomic force microscopy (AFM) in intermittent contact mode both ex situ and in situ. In the first case it is shown that negatively charged SPB only weakly interact with the negatively charged surface and exhibit a long-range two-dimensional surface order observed by atomic force microscopy. In comparison the phase information obtained by AFM is strikingly different on the particles of both SPB types. The positive polyelectrolyte chains of the cationic SPB spread on the surface and are responsible for a corona around the particles as revealed by AFM. In this case no long-range order was observed. The shell of the SPB and its charge hence can be used to tune the interaction of the particles with solid substrates within a wide range.