STUDY OF SOL-STATE PROPERTIES OF AQUEOUS GELATIN SOLUTIONS

Aqueous gelatin solutions have been studied in a systematic and exhaustive manner in a neutral buffer medium, in the temperature range of 30-60 degrees C, by static (SLS) and dynamic laser light scattering. It has been clearly established that upon cooling the sol from 60 degrees C, the gelatin chains form thermoreversible aggregates until the gelation is encountered below 30 degrees C. The radius of gyration of the chains (R(g)) at any temperature was found to scale with corresponding molecular weight as R(g) similar to M(w)(0.57+/-0.03). The ratio of R(g) to hydrodynamic radius R(H) has been found to be R(g)/R(H)=1.82+/-0.03 as expected for random coils. The translational diffusion coefficient of the chains D-Z(c) exhibited linear concentration dependence; D-Z(c)=D-0(1+K(D)c) and D-0 similar to M-0.57+/-0.03. The second virial coefficient (A(2)) of osmotic pressure obtained through SLS could be excellently related to K-D through K-D similar or equal to 2A(2)M(w) for all temperatures. The Flory-Huggins interaction parameter chi was determined to be chi similar or equal to 0.48 and it showed negligible temperature dependence. The temperature dependence of sol viscosity eta(T) could be fitted to Doolittle equation In eta(T)=A+B/T. At any given temperature, the concentration dependence of specific viscosity eta(sp)(C) followed eta(sp)(c)/c=1/([eta]+k root c). The intrinsic viscosity [eta] was found to scale with M(w) as [eta]similar to M(w)(0.69+/-0.08) also yielding a typical overlap concentration of c*similar or equal to 2.5 % (w/w). The Flory-Fox constant Phi was found out to vary between 2.66x10(21) at 35 degrees C and 1.27X1021 at 60 degrees C, against the standard value of 2.21X10(21). The density values of the sol have been measured by a simple but novel method. Both the sol density and refractive index show monotonous increase as the gel point is approached from the hot sol state of gelatin.