Structure-properties relation for agarose thermoreversible gels in binary solvents

The structure of agarose gels prepared in aqueous binary solvents has been studied by means of X-ray and neutron small-angle scattering. The scattering curves are interpreted by considering a random assembly of straight fibers displaying cross-section polydispersity. The cross-section polydispersity is well accounted for with a distribution function of the type w(r) similar to r(-lambda) bounded by two radii, r(min) and r(max), and where lambda depends upon both the nature of the binary solvent and the agarose concentration. Departure from the Pored regime at wide scattering angles suggests the existence of free and/or dangling chains that do not participate in the network elasticity (loose chains). The fraction of loose chains gradually vanishes upon increasing the agarose concentration. Experimental elastic modulus-concentration relations obtained on the same type of samples point to the occurrence of entropic elasticity once analyzed in light of the existence of loose chains. Entropic elasticity is rather consistent with disorganized gel junctions.