Holographic relaxation spectroscopic study on the structure of gelatin gel doped with fluorescein as a tracer

The structures of gelatin gels have been studied by holographic relaxation spectroscopy (HRS) with fluorescein as a doped tracer. An HRS spectrum with double peaks has been observed. It has been experimentally proven that this anomalous HRS spectrum is related to the structures of the gelatin gels. It is shown that two kinds of gel networks are formed when a gelatin solution is cooled at a rate of 2°C/min to a temperature below the gel temperature. Microviscosity inside one kind of network is about four times lower than inside the other one. One with lower microviscosity is called a coarse network, and it is formed through aggregation of a collagen-like, triple-stranded helix. The other is named a fine network and it is constructed simply by entanglements between polymer chains. The structure of gelatin gel can be considered as a blend of these two networks. By controlling the cooling speed, the structure of gelatin gels can be dominated by either coarse or fine gel networks.Dedicated to Prof. Dr. W. Pechhold on the occasion of his 60th birthday.