Surface properties of gelatin films

Contact angle measurements for water, glycerol, formamide, ethylene glycol, diiodomethane, alpha-bromonaphthalene, tricresyl phosphate, dimethylsulfoxide (DMSO), and bromoform on polymethyl methacrylate, (PMMA) covered with adsorptive and gelatinized gelatin films were made, Adsorption was performed from solutions in the 0-25 g/L concentration range. A gelatinized gelatin film was created from solutions of 40-100 g/L concentrations. It was found that the biggest changes of the contact angles wore up to monolayer coverage of the PMMA, surface, For all liquids (besides water) the contact angle was almost constant above the gelatin concentration 50 g/L. Very high contact angles (similar to134degrees) were obtained for water on a gelatinized gelatin film obtained from a solution of 100 g/L concentration, Front the obtained contact angles, the Lifshitz-van der Waals components and the values of the electron-acceptor and electron donor parameters of the acid-base components of the films were calculated for the glycerol-ethylene glycol diiodomethane three-liquid system. It was found that the water contact angle strongly influenced the Lifshitz van der Waals component and acid-base parameters of the gelatin film surface free energy. The systems involving water gave different results than those without water. It was found that the values of the gelatin film surface free energy components and parameters cannot be explained only on the basis of the functional group's orientation in gelatin molecules. To find an explanation, back-calculations of the contact angle for water, formamide, a-bromonaphthalene, tricresyl phosphate, dimethylsulfoxide, and bromoform were made. The authors found a good agreement between the calculated and measured values of the contact angle for all liquids studied, besides water and, partially, DMSO. To explain the obtained results of the measured contact angles, four models of hydratation of gelatin films were presented.