Internal structures of agar-gelatin co-hydrogels by light scattering, small-angle neutron scattering and rheology

Internal structures of agar-gelatin co-hydrogels were investigated as a function of their volumetric mixing ratio, $\ensuremath r=[\mathrm{AG}]:[\mathrm{Ge}]=0.5$ , 1.0 and 2.0 using dynamic light scattering (DLS), small-angle neutron scattering (SANS) and rheology. The degree of non-ergodicity ( $\ensuremath X=0.2\pm0.02$ , which was extracted as a heterodyne contribution from the measured dynamic structure factor data remained less than that of homogeneous solutions where ergodicity is expected (X = 1 . The static structure factor, I(q) , results obtained from SANS were interpreted in the Guinier regime (low-q , which implied the existence of $ \approx$ 250 nm long rod-like structures (double-helix bundles), and the power law (intermediate-q regions yielded $\ensuremath I(q)\sim q^{-\alpha}$ , with $ \alpha$ = 2.3 , 1.8 and 1.6 for r = 0.5 , 1.0 and 2.0. This is indicative of the presence of Gaussian chains at low r , while at r = 2 there was a propensity of rod-shaped structures. The gel strength and transition temperatures measured from frequency sweep and temperature ramp studies were suggestive of the presence of a stronger association between the two biopolymer networks at higher r . The results indicate that the internal structures of agar-gelatin co-hydrogels were highly dependent on the volumetric mixing ratio