The changes of the surface free energy of the adsorptive gelatin films

Measurements of the contact angles for water (W), formamide (F), ethylene g lycol (E) and diiodomethane (D) on polymethyl methacrylate (PMMA) covered b y adsorptive gelatin films were made. Adsorption was performed from solutio ns in the concentration range 0-100 g/l. It was found that the biggest chan ges of the contact angles were up to a monolayer coverage of PMMA surface. For all liquids (besides water) the contact angle was practically constant at gelatin concentration over 2 g/l. Based on these contact angle data, it was suggested that the adsorptive gelatin film structure depended on the co ncentration of the aqueous gelatin solution from which the adsorption was p erformed. On the basis of the contact angles obtained the Lifshitz-van der Waals comp onents and the values of the electron-acceptor and electron-donor parameter s of the acid-base components of the films were calculated for three triple ts of liquids (W-F-D, W-E-D and F-E D). It was found that the water contact angle strongly influenced the Lifshitz-van der Waals component and acid-ba ss parameters of the gelatin film surface free energy. Systems involving wa ter gave different results than those without water. It was concluded that the gelatin film had a monopole electron-donor character and that this char acter was caused by the existence of carbonyl or ionised carboxyl groups on gelatin film surface. (C) 2001 Elsevier Science Ltd. All rights reserved.