J. Phys. II France
Volume 2, Numéro 8, August 1992
Page(s) 1617 - 1629
DOI: 10.1051/jp2:1992224
J. Phys. II France 2 (1992) 1617-1629

Molecular structure of poly methyl methacrylate thermoreversible gels

Nazir Fazel1, 2, Zarmina Fazel1, Annie Brûlet3 and Jean-Michel Guenet1

1  Laboratoire d'Ultrasons et de Dynamique des Fluides Complexes, Université 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
3  Laboratoire Léon Brillouin (CEA-CNRS), CEN Saclay, F-91191 Gif-sur-Yvette Cedex, France

(Received 17 March 1992, accepted in final form 30 April 1992)

The molecular structure of PMMA gels and aggregates in bromobenzene and ortho-xylene has been investigated by small-angle neutron scattering. It is found that in bromobenzene the gels are constituted of connected, prolate cylinder-like structures. A large proportion of these structures (about 90 %) possess a radius of about 1.5 nm. The remaining possess larger radii (from 3.0 to 5.3 nm). On heating, the melting process seems to proceed via two-steps : melting of the junction domains while the cylinder-like structures remain virtually unaffected. Scattering curves that differ significantly are obtained in ortho-xylene. They are also interpreted with cylinder-like objects of larger radii (up to 10 nm). As with bromobenzene, melting seems to take place in two steps. These results prove to be relevant for interpreting rheological data that will be presented in a forthcoming paper.

61.12 - 81.20S - 82.70

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