Hofmeister Effects of Monovalent Sodium Salts in the Gelation Kinetics of Gelatin.

The gelation kinetics of gelatin depends on the presence of electrolytes, and the influence of cations with variable valency has been recently emphasized. However, acquired knowledge shows that the nature of anions has more influence on various properties of aqueous solutions than the nature of the cations. It is shown herein, using sodium salts of monovalent anions, that the gelation kinetics of gelatin is accelerated by the presence of highly kosmotropic anions like fluoride and strongly slowed, eventually inhibited, by the presence of chaotropic anions like thiocyanate and perchlorate. Overall the parameter characterizing the gelation kinetics, k, is a linear function of the polarizability of the used salt in aqueous solution, which has been quantified independently by refractometry and using the Lorentz-Lorenz formula. It is also found that the same parameter characterizing the gelation kinetics is a linear function of the viscosity B coefficient taken from the literature. The linear correlation coefficients are excellent in the case of halide anions (F-, Cl-, Br-, I-) but poorer when nonspherical anions like NO3-, SCN-, and ClO4- are considered.