Transient electric birefringence study of agarose aggregates in water‐dimethyl sulphoxide mixtures

The dynamical behavior of agarose aggregates in a mixture of water and dimethyl sulphoxide (DMSO) has been investigated using a Transient Electric Birefringence (TEB) set up. Different agarose concentrations for different water/DMSO proportions were considered. The relaxation of the birefringence curves can be fitted with a stretched exponential of the form Δn(t) = Δn0 exp(‐(Dt) 0.5 ). The exponent 0.5 suggests a high polydispersity of the aggregates. The rotational diffusion coefficient, D, depends strongly on the water/DMSO proportion. For small values of the applied electric field it presents a maximum for a water volume fraction equal to 0.5. A strong dependence of D on the applied electric field is also observed. However, the same kind of behavior as for weak fields is recovered when a subtle representation of the data is used. Differential Scanning Calorimetry (DSC) results also show a maximum in the temperature of fusion of the aggregates for a water volume fraction of 0.5. This set of results suggest strongly that « complexes » of water/DMSO/agarose are formed in the mixture and that the process of aggregate formation is more « efficient » for a water/DMSO mixture of same proportions.