Viscometric Study of the Gelatin Solutions Ranging from Dilute to Extremely Dilute Concentrations

The viscosity of gelatin solutions with concentrations between 10(-4) and 10(-5) g/cm(3), covering the extremely dilute zones, was studied via a photoelectric viscometer, and the effects of the electrolyte, pH, surfactant, urea, and temperature were discussed. The results showed that the reduced viscosity (eta(sp)/C) of gelatin exhibited a drastic increase with dilution in the extremely dilute aqueous solutions, this being a typical polyelectrolyte effect. The reduced viscosity of gelatin underwent several oscillations with varying pH; the minimum value of the viscosity was at pH = 5.0, corresponding to its isoelectric point, where gelatin exhibited antipolyelectrolyte behavior. The reduced viscosity of gelatin decreased with increasing temperature, which was due to the helix-coil transition in the gelatin solution. The temperature of the helix-coil transition was 30.0 degrees C in gelatin aqueous solution; however the temperature of helix-coil transition decreased to 20.0 degrees C in urea. Upon cooling, the gelatin molecules in aqueous solution underwent a coil-helix transition. Hydrophobic interactions caused chain folding in the presence of the surfactant sodium dodecylsulphate.