Abstract
The dynamic behaviour of agarose aggregates grown in binary mixtures of water and dimethyl sulphoxide (DMSO) has been investigated by Transient Electric Birefringence (TEB). Different agarose concentrations in various water/DMSO compositions have been studied. The birefringence relaxation has been fitted by means of a stretched exponential with an exponent of 0.5 which suggests highly size-polydispersed aggregates. The rotational diffusion coefficient, 〈Drot〉, has been seen to depend strongly upon the composition of the binary solvent and to increase markedly with increasing electric field. The gradient d〈Drot〉/dE has been thus considered a relevant parameter. For low agarose concentrations d〈Drot〉/dE displays a maximum for a solvent composition in the vicinity of fDMSO=0.17 (mole fraction). Also, d〈Drot〉/dE varies as a power of concentration whose exponent first increases with increasing DMSO proportion and then levels off at nearly the same mole fraction (i.e. fDMSO=0.17). The results are discussed in the light of the occurrence of a ternary complex (agarose/water/DMSO), a model of organization within the agarose fibres recently proposed from thermodynamics investigations.
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