The swelling of gelatin films. The effects of drying temperature and of conditioning the layers in atmospheres of high relative humidity

Abstract

Gelatin layers show minimum swelling when the temperature of the layer during drying is about 35°. When dried at a higher temperature, the layer is ‘so‐like’ and bonding does not occur until the layer is swollen or conditioned at a high relative humidity. Sol‐like layers of non‐de‐ionised gelatin when swollen in distilled water swell rapidly to a maximum value and then contract to a final value. De‐ionized sol‐like layers swell straight to this final value. The overshoot with the non‐de‐ionized layers is believed to be due to osmotic forces within the layers, which disappear when the salts are washed out. When conditioned in an atmosphere of high relative humidity, all layers afterwards show a reduced swell. The reduction is very large and very rapid for sol‐like layers. The results are explained by assuming that bonds formed during setting and drying are under no strain at the time of their formation and will tend to resist any compressive or tensile strains caused by drying or by increased swelling, respectively. The number and the strength of the bonds will be controlled by the drying conditions.