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

Plots of relative viscosity eta(rel) versus gelatin concentration in a queous solution were subjected to quantitative analysis near the sol-g el transition. Peak intensity of the high-resolution NMR line at 0.93 ppm associated with the protons df methyl groups of amino acid residue s in gelatin was also examined near the helix-coil transition. Gelatin s from various sources and isolated by various procedures were studied . Within the framework of concepts treating draining in three-dimensio nal systems, scaling relationships relating hydrodynamic volume of fra ctal clusters of dimensionality D, the number of clusters, and eta(rel ) were obtained. It was demonstrated that on the branch of a percolati on cluster (D = 2.5), eta(rel),el is controlled by the intrinsic visco sity [eta](0), concentration c, and the number of particles (s) over b ar comprising the cluster; the reduced time tau for the sol-gel transi tion is given as (1 + tau)(3/2) = 1n eta(rel) ([eta](0)c). Expressions describing the variation of probability for the formation of an infin ite cluster, and those for concentration and mean size of finite clust ers were obtained. The width of the sol-gel transition and critical pa rameters of gelation in solution(concentration, cluster size as deduce d from viscosity measurements) and the width Delta T/T of the helix-c oil transition according to NMR spectroscopy were found to be controll ed by hydrodynamic volume V-0 of macromolecules. Moreover, correlation between the parameters of cooperativity of segmental mobility accordi ng to Zimm-Bragg and V-0 was observed.