Wettability of starch gel films

Contact angles for water, glycerol, formamide, ethylene glycol and diiodomethane on polymethyl methacrylate (PMMA) covered by gelatinized corn and potato starch films were measured and statistically no significant differences between them were found. The contact angles were correlated with starch content in a gel and a straight linear relationship was confirmed by making use of Student t-test. Using this correlation the Lifshitz–van der Waals component and electron-acceptor and -donor parameters of the acid–base components of the film surface free energy were calculated. The obtained relationship between the Lifshitz–van der Waals component and starch content in a gel was also linear. Linear relationships were also obtained for the electron-acceptor and -donor parameter as a function of starch content in a gel film. For the Lifshitz–van der Waals component and electron-acceptor parameter a very small decrease was observed. This component decreased from 33.7 to 31.4 mJ/m2 for corn gel and from 32.7 to 31.0 mJ/m2 for potato gel, and the electron-acceptor parameter decreased from 1.4 to 0.6 mJ/m2 for corn gel and from 1.3 to 0.8 mJ/m2 for potato gel. However, the electron-donor parameter increased substantially from 31.2 to 70.6 mJ/m2 for corn gel and from 32.2 to 63.3 mJ/m2 for potato gel. It was suggested that starch gel surface attempted to maintain maximal hydrophobic character with polar domains formed by functional groups of d-glucose units.