Surface Mobility of Grafted Hydrogels

Solid-supported hydrogels were prepared by ozone-induced graft polymerization of 2-hydroxyethyl methacrylate (HEMA), diethylene glycol methacrylate (DEGMA), and triethylene glycol methacrylate (TEGMA) onto polypropylene substrates. Angle-dependent ESCA showed a gradient in chemical composition in the near-surface region (thickness 55 Å). The various shapes of the C 1s peaks collected at a takeoff angle of 45° corresponded to what could be expected from the chemical composition of polyHEMA, polyDEGMA, and polyTEGMA, respectively. At a takeoff angle of 15°, all grafted polymers showed a more hydrophobic character with respect to the shape of the C 1s peak. During dynamic contact angle measurements, HEMA-grafted fibers showed the largest contact angle hysteresis, with an advancing contact angle of about 90° and receding contact angle close to zero. A less pronounced contact angle hysteresis for both DEGMA and TEGMA-grafted fibers was explained by a hindered reorientation as a consequence of an increased side chain length of the grafted polymers. A suppressed contact angle hysteresis was also obtained for fibers grafted in a HEMA monomer mixture containing 5% cross-linker (EDMA). Such surfaces also showed good reproducibility when sequential wetting cycles were performed during the dynamic contact angle measurements.