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/cm³, 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 (η_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°C in gelatin aqueous solution; however the temperature of helix–coil transition decreased to 20.0°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.