Hierarchical structures in agar hydrogels

Abstract

Small angle neutron scattering experiments were performed on agar solutions and gels to explore their differential microscopic structures. In solution state, the wave vector, q, dependence of static structure factor, I(q), could be described by I(q)=Igexp(−q2Rg2/3)+IRq−α. Statistical analysis gave: Rg=18nm and α=0.85±0.07 indicating the existence of rod-like rigid structures of length, L=12Rg≈63nm. In gels, I(q)=IGexp(−q2Ξ2)+IFq−β+(IP/q)exp(−q2Rc2/2) which had discernible Gaussian, power-law and Kratky–Porod regimes in the low, intermediate and high-q regions. Regression analysis yielded a characteristic length, Ξ=3.3−4nm for gels with agar concentration, c=0.1−0.3% (w/v). The exponent β=1.2±0.2 and the cross-sectional radius of cylindrical fibres, Rc=1.5±0.3nm remained invariant of agar concentration. This assigned a value 5nm to the persistence length of the fibres in the solution phase that reduced to 3nm in the gel phase indicating differential hydration of the fibres.