Correlation between the viscoelastic properties of a soft crystal and its microstructure
E. Eiser1 - F. Molino2 - G. Porte2
1 European Synchrotron Radiation Facility, BP 220,
F-38043 Grenoble Cédex, France
2 Groupe de Dynamique des
Phases Condensées, Université de Montpellier II, F-34095
Montpellier Cedex 05, France
porte@gdpc.univ-montp2.fr
Received on 4 June 1999 and Received in final form 6 September 1999
Abstract
We investigate the rheological properties of a cubic fcc
phase of micelles obtained by aggregation of a triblock copolymer
(PEO)127(PPO)48(PEO)127 in water as selective
solvent. The resulting soft solid is submitted to a range of
stresses varying from 20 to 800 Pa in Couette geometry.
Creep and flow behaviour can be distinguished
and interpreted in terms of structural changes previously observed
by SAXS under flow. Contrasting with other systems, no
discontinuity in the flow behaviour is associated with the
structural changes. The strong shear thinning is interpreted from
the scattering data, as resulting from the nucleation of a new
structure of hexagonal compact planes parallel to the Couette
walls. This creates a lubricating domain in the gap, whose size
grows with the applied shear rate. We argue moreover that the
very existence of flow (as a steady state opposed to creep) is
associated with this so-called layer-sliding structure in a
fraction, however small, of the sample.
PACS
83.10.Hh Flow of solids -
83.10.Lk Multiphase flows -
83.20.Hn Structural and phase changes
Copyright EDP Sciences, Società Italiana di Fisica, Springer-Verlag
