Probing biopolymer films with scanning force methods

Scanning force microscopy of thin gelatin films on mica reveals two distinct film components with characteristic frictional, morphological and adsorptive signatures. A high-friction film 14 nm thick completely wets the mica surface, while a low-friction minority component is present primarily as porous islands on top of the high-friction layer. Additional domains of extremely high friction within the majority component are detected in frictional images obtained with a blunt, gelatin-covered tip; no corresponding topographic differences are imaged. A high-force scanning procedure remarkably transforms the majority component into the low-friction phase if a sufficient amount of water is present in or on the film. The nanostructure of both components is imaged using a nanometer-scale asperity of gelatin attached to the SFM tip. The anticipated network structure of gelatin is observed on the high-friction majority phase. The low-friction phase is interpreted as moieties of intramolecularly-folded gelatin, with thickness (1.5±0.2 nm) equal to the diameter of the collagen-fold triple helix, containing substantial structural water.