PHASE-SEPARATION OF AQUEOUS-SOLUTION OF METHYLCELLULOSE

As we determined visually by the temperature cloud point method, the c oexistence phase curve of methylcellulose in aqueous solution belongs to the LCST (low critical solution temperature) type. Rheological dyna mic measurements reveal the existence of three gel domains. The gel (I ) localized in the homogeneous phase at low concentration and low temp erature, is a very weak gel, where the cross-links are attributed to p airwise 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 attribu ted to the formation of crystallites which play the role of cross-link ing points. The third gel was concomitant to the micro-phase separatio n. In these turbid gels, syneresis develops slowly with time: the high er the temperature and the lower the concentration: the faster the syn eresis. Near the three sol-gel transitions, a power law frequency depe ndence of the loss and storage moduli was observed and the viscoelasti c 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.