Phase separation of aqueous solution of methylcellulose

As we determined visually by the temperature cloud point method, the coexistence phase curve of methylcellulose in aqueous solution belongs to the LCST (low critical solution temperature) type. Rheological dynamic measurements reveal the existence of three gel domains. The gel (I) localized in the homogeneous phase at low concentration and low temperature, is a very weak gel, where the cross-links are attributed to pairwise hydrophobic interactions between the most hydrophobic zones of the backbone: the trimethyl blocks. The second gel (II) was revealed in the high concentration regime and below the LCST, it may be attributed to the formation of crystallites which play the role of cross-linking points. The third gel was concomitant to the micro-phase separation. In these turbid gels, syneresis develops slowly with time: the higher the temperature and the lower the concentration: the faster the syneresis. Near the three sol-gel transitions, a power law frequency dependence of the loss and storage moduli was observed and the viscoelastic exponent Delta(G' similar to G '' similar to omega(Delta)) was found to be 0.76 and 0.8 and to reach 1 at high concentration.