| Abstract: | A structural transition is reported to occur in aqueous sols of agarose, an electrically uncharged biostructural polysaccharide. The transition has no measurable effect on size dispersity on the shape of the solute polysaccharide as observed by precision photon correlation spectroscopy. It originates a low-angle pattern of scattered light similar to that which monitors phase separations in polymer blends. Thus, it must be due to some extent to spatially modulated polymer clustering, typical of spinodal decomposition. In the interval of temperatures studied, it precedes very distinctly in time the thermoreversible sol–gel transition, which is known to be promoted at higher concentrations. It also anticipates to an appreciable extent the spatial density modulation observed in the gel. Although reported here for the first time, a spinodal decomposition of the sol that precedes and possibly triggers the processes leading to gelation does not come unexpectedly in terms of site-bond correlated-percolation theory. In general, this occurrence raises the question as to whether the spontaneous onset of regions of higher and lower polymer concentration (spinodal separation) may be regarded as a novel path for biomolecular interactions and the self-assembly of order in biomolecular systems. |
