AQUEOUS-SOLUTIONS OF GELATIN NEAR THE GELATION THRESHOLD - SCALING BEHAVIOR, CLUSTER STRUCTURE, AND CONCENTRATION PLOTS FOR RELATIVE VISCOSITY

Plots of relative viscosity eta(rel) versus gelatin concentration in aqueous solution were subjected to quantitative analysis near the sol-gel transition. Peak intensity of the high-resolution NMR line at 0.93 ppm associated with the protons df methyl groups of amino acid residues in gelatin was also examined near the helix-coil transition. Gelatins from various sources and isolated by various procedures were studied. Within the framework of concepts treating draining in three-dimensional systems, scaling relationships relating hydrodynamic volume of fractal clusters of dimensionality D, the number of clusters, and eta(rel) were obtained. It was demonstrated that on the branch of a percolation cluster (D = 2.5), eta(rel),el is controlled by the intrinsic viscosity [eta](0), concentration c, and the number of particles (s) over bar comprising the cluster; the reduced time tau for the sol-gel transition is given as (1 + tau)(3/2) = 1n eta(rel) ([eta](0)c). Expressions describing the variation of probability for the formation of an infinite cluster, and those for concentration and mean size of finite clusters were obtained. The width of the sol-gel transition and critical parameters of gelation in solution(concentration, cluster size as deduced from viscosity measurements) and the width Delta T/T* of the helix-coil transition according to NMR spectroscopy were found to be controlled by hydrodynamic volume V-0 of macromolecules. Moreover, correlation between the parameters of cooperativity of segmental mobility according to Zimm-Bragg and V-0 was observed.