Physical Networks of Metal-Ion-Containing Polymer Brushes Show Fully Tunable Swelling, Nanomechanical and Nanotribological Properties

Abstract

The interaction between weak polyacid brushes and metal ions can lead to the formation of a wide variety of complex structures across the polymer grafts. In the case of poly(hydroxyethyl methacrylate) brushes derivatized with succinate side groups (PHEMA-SA), the coordination with Zn2+ or Ca2+ species can be tuned by varying the solution pH, below and above the pKa of the polyacid brush. Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) indicates that Zn2+ ions generate relatively weak, localized monodentate bridges along PHEMA-SA grafts at basic pH. These Zn2+–brush conjugates swell profusely in water, are compliant and very lubricious, as observed by combining variable angle spectroscopic ellipsometry (VASE), quartz crystal microbalance with dissipation (QCM-D), and atomic force microscopy (AFM) methods. In contrast, incubation of PHEMA-SA brushes with Ca2+ or Zn2+ at acidic pH leads to the formation of more extended, bidentate linkages forming a physical network between the...