Influence of thermal history on the structural and mechanical properties of agarose gels

Using a multitechnique approach, two temperature domains have been identifi ed in agarose gelation. Below 35 degreesC, fast gelation results in strong, homogeneous and weakly turbid networks. The correlation length, evaluated from the wavelength dependence of the turbidity, is close to values of pore size reported in the literature. Above 35 degreesC, gelation is much slowe r and is associated with the formation of large-scale heterogeneities that can be monitored by a marked change in the wavelength dependence of turbidi ty and visualised by transmission electron microscopy. Curing agarose gels at temperatures above 35 degreesC, and then cooling them to 20 degreesC, pr oduces much weaker gels than those formed directly at 20 degreesC. Dramatic reductions in the elastic modulus and failure strain and stress are Sound in this case as a result of demixing during cure. An interpretation, based on the kinetic competition between osmotic forces (in favor of phase separa tion) and elastic forces (that prevent it) is proposed. (C) 2001 John Wiley & Sons, Inc.