GELATION OF GELATIN OBSERVATION IN THE BULK AND AT THE AIR-WATER-INTERFACE

Gelation of gelatin under various conditions has been followed by atom ic force microscopy (AFM) with the objective of understanding more ful ly the structure formed during the gelation process. AFM images were o btained of the structures formed from both the bulk sol and in surface films during the onset of gelation. While gelation occurred in the bu lk sol, the extent of helix formation was monitored by measurements of optical rotation, and the molecular aggregation was imaged by AFM. In terfacial gelatin films formed at the air-water interface were also st udied Measurements of surface tension and surface rheology were made p eriodically and Langmuir-Blodget films were drawn from the interface t o allow AFM imaging of the structure of the interfacial layer as a fun ction of time. Structural studies reveal that at low levels of helical content the gelatin molecules assemble into aggregates containing sho rt segments of dimensions comparable to those expected for gelatin tri ple helices. With time larger fibrous structures appear whose dimensio ns suggest that they are bundles of triple helices. As gelation procee ds, the number density of fibers increases at the expense of the small er aggregates, eventually assembling into a fibrous network. The gel s tructure appears to be sensitive to the thermal history, and this is p articularly important in determining the structure and properties of t he interfacial films. (C) 1998 John Wiley & Sons, Inc.