Adsorption of amphiphilic diblock copolymer micelles at the mica/solution interface

The adsorption of the amphiphilic diblock copolymer poly(2-(dimethylamino)e thyl methaerylate-blockmethylmethaerylate) (DMA-MMA) at the mica/solution i nterface has been studied, over a range of solution pH values, using in sit u atomic force microscopy. In contrast to the adsorption of the homopolymer poly(2-(dimethylamino)ethyl methacrylate (DMA), which exhibited a featurel ess adsorbed layer, adsorbed layers of the DMA-MMA copolymer exhibited late ral structure at all pH values studied. At low solution pH, images of the a dsorbed layer reveal discrete domelike structures, separated by regions wit h no lateral features. Force-distance data recorded between these domes ind icate adsorption in the form of positively charged material. It is proposed that the adsorbed layer forms via the adsorption of DMA-MMA micelles direc tly to the mica surface, followed by relaxation of the DMA chains to the su rface. This relaxation is driven by electrostatics and results in an adsorb ed layer that is essentially a layer of DMA chains with the MMA cores protr uding as domes at the sites of the original micelle adsorption. The domes a re evident over the entire surface, although arranged in a disordered manne r. The distance between the domes is seen to decrease as the pH of the adso rbing copolymer solution is increased from 4 to 7, due to the increased num ber of negatively charged adsorption sites on the mica surface. Adsorption of charged latex particles shows that objects without molecular freedom ads orb in a close-packed manner. Close packing of adsorbed units is also obser ved when the DMA-MMA micelles are adsorbed from a solution at natural pH pH 8.3), where the relaxation of the coronal DMA chains is electrostatically hindered.