J. Phys. II France
Volume 2, Numéro 9, September 1992
Page(s) 1745 - 1754
DOI: 10.1051/jp2:1992231
J. Phys. II France 2 (1992) 1745-1754

Swelling and rheological properties of poly methyl methacrylate thermoreversible gels

Zarmina Fazel1, Nazir Fazel1, 2 and Jean-Michel Guenet1

1  Laboratoire d'Ultrasons et de Dynamique des Fluides Complexes, Universtié Louis Pasteur, CNRS URA 851, 4 rue Blaise Pascal, F-67070 Strasbourg Cedex, France
2  Laboratoire de Physique des Liquides et Interfaces, Université de Metz, 57070 Metz Cedex, France

(Received 17 March 1992, accepted in final form 9 June 1992)

The stress relaxation as well as the variation of the isochrone compression modulus as a function of concentration have been studied with PMMA thermoreversible gels. Two solvents have been used : bromobenzene and ortho-xylene. The swelling behaviour has also bee examined. Only gels in bromobenzen swell significantly. The swelling ration vs. polymer concentration has been interpreted by means of a theory derived for two-phase systems. In both solvents considerable stress relaxation is observed. In the early stage this relaxation obeys a power law $(\sigma \approx t^{-m})$ with $m\approx 0.08$ to 0.13 in bromobenzene and 0.23 in ortho-xylene. For this reason isochronal moduli at 120 s have been considered. Modulus-concentration relations are as follows : $E\approx C_{\rm p}^{1.86}$ for non-swollen gels in bromobenzene, $E\approx C_{\rm p}^{1.99}$ for gels swollen to equilibrium in bromobenzene, $E\approx C_{\rm p}^{2.66}$ in ortho-xylene. These results are discussed by means of theories developed for rigid gels in the light of the molecular structure determined by small-angle neutron scattering (preceding paper published in the issue of August).

46.30J - 81.20S - 82.70

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