Drying dissipative structures of gelatin solution

Macroscopic and microscopic drying patterns formed from aqueous gelatin solutions on a cover glass were studied as a function of gelatin concentration and temperature. Specific drying patterns were observed within the circular dried film resulting from a droplet of the solution (0.1 ml) placed on the cover glass surface when the droplet evaporated. Two broad rings formed at the outside edge of the dried film and the inner area. d _f /d _i values of the inner broad rings decreased sharply with increasing gel concentration, where d _f is the final size of the broad ring in the dried film and d _i is the size of initial liquid in diameter. Thickness profiles of the dried film changed sharply from the broad ring to the round hill at the center as gelatin concentration increased. The sharpness parameter S (or S′) were evaluated from the ratio of the film size (diameter) against the full widths at half maximum (or the full widths at the bottom layer) in the thickness profiles of the broad ring and/or the round hill. The S (or S′) values changed transitionally at the critical concentration and temperature of gelation. The gelation of gelatin collagen was resulted in the disturbed convectional diffusion of solutes during dryness. The round hill-like thickness profile at the high polymer concentration and at low temperature also supports the gelation. These observations support that gelation process of collagen molecules is followed from decrease in S (or S′) values in the macroscopic patterns. Dendritic, hedrite, and/or spherulite microscopic drying patterns were observed especially in the central area and at low temperatures.