Competitive adhesion reduces the effective bridging length of polymers
Résumé
Surface end-grafted poly(acrylic acid) (PAA) chains were investigated by AFM-based single molecule force spectroscopy. Upon adsorption on the surface of the AFM tip, the molecules bridge the two surfaces. By retracting the tip from the sample, the molecules were desorbed from the tip surface and the bridging lengths were measured. The comparison of the observed bridging length distribution with the molecular length distribution as obtained by GPC revealed that tip and sample surface compete for the polymer. In the case of higher adsorption strength to the tip surface the polymer chains bridge with their entire lengths while in the opposite case the polymers try to maximize the surface coverage. In the latter, the bridging lengths are reduced depending on the grafting density of the polymer monolayer. © 2008 American Chemical Society.