STUDIES OF THE SWELLING AND DRYING KINETICS OF THIN GELATIN GEL FILMSBY IN-SITU INTERFEROMETRY

Both the swelling and drying kinetics of thin gelatin gel films were s tudied by in situ interferometry. Both a novel interferometry sensor a nd a conventional interferometer were used. One of the advantages of u sing the in situ interferometers is that the experimental time require d to reach final swelling equilibrium has been reduced from hours, or even days, to minutes. The basic principle of in situ interferometry i s illustrated. Our swelling experimental data can be better fitted by the first-order kinetics than by the suggested second-order one in lit eratures. This apparent contradiction has been discussed in terms of t he difference in the size of gelatin gel. The experimental data obtain ed in the drying process show that the film-drying rate increases with time, while according to the general gel-shrinking theory developed b y Li and Tanaka the gel-shrinking rate should decrease with time. We h ave shown that the deviation might be attributed to the intrinsic diff erence between the drying and shrinking processes, i.e., one is in dry air and another is in solvent, and to the nature of gelatin gel. In a ddition, the ratio of the shear modulus over the longitudinal modulus and the cooperative diffusion coefficient were also estimated from the swelling experimental results.