SPONTANEOUS SYMMETRY-BREAKING PATHWAYS - TIME-RESOLVED STUDY OF AGAROSE GELATION

Extensive time-resolved studies of self-assembly of agarose gels, perf ormed with the use of a variety of techniques allowed identification o f the initial break of symmetry and the actual path leading to self-as sembly at concentrations well below the random percolation threshold. The overall process is seen to occur through the following sequence: ( i) break of symmetry in the sol, causing the spontaneous generation of mesoscopic polymer-rich and solvent-rich regions; (ii) percolation, o r nearly percolation [see (iv) below], of polymer-rich regions through the sample, still in the sol state; (iii) start of polymer cross-link ing within polymer-rich regions; (iv) progress of cross-link percolati on, channeled along the pathways of polymer-rich regions. The analogou s role of either permanent or transient demixing of the sol in providi ng preferential paths for cross-links and promoting gelation at modera te and low concentrations has been established also in a variety of ot her biopolymeric systems.