Adsorption of Spherical Polyelectrolyte Brushes : from Interactions to Surface Patterning

Abstract

Adsorption of colloidal particles constitutes an attractive route to tailor the properties of surfaces. However, for efficient material design full control over the particle-substrate interactions is required. We investigate the interaction of spherical polyelectrolyte brushes (SPB) with charged substrates based on adsorption studies and atomic force spectroscopy. The brush layer grafted from the colloidal particles allows a precise adjustment of their adsorption behavior by varying the concentration of added salt. We find a pronounced selectivity between oppositely and like-charged surfaces for ionic strengths up to 10mM. Near the transition from the osmotic to the salted brush regime at approximately 100mM attractive secondary interactions become dominant. In this regime SPB adsorb even to like-charged surfaces. To determine the adhesion energy of SPB on charged surfaces directly, we synthesize micrometer-sized SPB. These particles are used in colloidal probe AFM studies. Measurements on oppositely charged surfaces show high forces of adhesion for low ionic strengths that can be attributed to an entropy gain by counterion release. Transferring our observations to charge patterned substrates, we are able to direct the deposition of SPB into two-dimensional arrays. Considering that numerous chemical modifications have been reported for SPB, our studies could open exiting avenues for the production of functional materials with a hierarchical internal organization.