VOLUME EFFECTS OF AMYLOSE-WATER INTERACTIONS

Volume changes resulting from the sorption of water by amylose have been determined by a newly developed dilatometric procedure involving the dissolution in potassium hydroxide of samples previously equilibrated to a range of desired water contents. The data are represented by an empirical equation containing two exponentials. A theoretical expression including parameters obtainable from sorption isotherms was developed by which the volume changes could be resolved into contributions arising from contact adsorption and from adsorption in more distant layers. The contribution from the latter was very small amounting to a volume decrease of less than 0.04 mL/g of sorbed water. The contact adsorption, in contrast, produced very large volume decreases ranging from 0.47 mL in nearly dry samples to 0.32 mL/g of water for samples containing 0.14-0.29 g of water/g of dry amylose. The change in these values suggests more than one type of sorption site. Their large magnitude points to a mutual filling of molecular cavities by the participating species. © 1990, American Chemical Society. All rights reserved.