6533b834fe1ef96bd129de9c

RESEARCH PRODUCT

Spinodal demixing, percolation and gelation of biostructural polymers

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description

We present a variety of new experiments which concern the self-assembly of a polymeric network from homogeneous solutions of Agarose, a representative biostructural polysaccharide used for previous studies at our laboratories. They allow deriving a semi-quantitative phase diagram in the T, C plane. The diagram includes both the spinodal and gelation lines. Below a value of about 2% w/v, concentration is not sufficient for direct gelation; however, quenching of the sol from high temperatures to below the spinodal line initiates the spinodal demixing. The latter generates two sets of regions having respectively, higher- and lower-than-average polymer concentrations. In the higher-concentration regions the functional polymer-polymer interaction (that is, self-assembly) is favoured. In fact, as in the course of demixing the point representative of higher-concentration regions reaches the region below the gelation line, gelation is allowed and indeed observed to occur. This evidences the possibly more general role of spinodal demixing (extended to multi-component systems) as a pathway for specific, local and biofunctional enhancements of concentrations. At very low concentrations (e.g. 10−4 w/v) the kinetics of demixing is still observed to occur, but the set of higher-concentration regions is no longer percolative. In these conditions, gelation occurs only within each individual region, while the specimen remains free-running. This illustrates a novel aspect of the notion of non-gelling concentrations.