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Soft Matter and Biological Physics

Eur. Phys. J. E 4, 255-262

Shear modulus of polydomain, mono-domain and non-meso morphic side-chain elastomers: Influence of the nematic order

P. Stein1, N. Aßfalg2, H. Finkelmann2 and P. Martinoty1

1  Laboratoire de Dynamique des Fluides Complexes, Université Louis Pasteur, 4 rue Blaise Pascal, 67070 Strasbourg Cedex, France
2  Institut für Makromoleculare Chemie, Stefan Meier Str. 31, 79104 Freiburg, Germany


(Received 28 January 2000 and Received in final form16 October 2000)

We investigate the behavior of the complex shear modulus of a series of elastomers including mono-domain and poly-domain liquid crystal samples, and a non-mesomorphic sample. We find that the dynamics of the glass transition are strongly modified by the nematic order. This result explains why the truly elastic response of liquid crystal elastomers can only be observed in the isotropic phase at very high temperatures and at very low frequencies. Between the elastic regime and the glassy state, the elastomers have a visco-elastic regime, which is characterized by a Rouse-like behavior for mono-domain and poly-domain samples, and by a Zimm-like behavior for the non-mesomorphic sample. We also show that the mono-domain sample exhibits marked anisotropy of the shear-modulus $G^\prime$. This anisotropy, which is observed for the first time, is a function of frequency and is inverted between low and high frequencies, due to relaxation effects of the orientational order.

83.80.Dr - Elastomeric polymers.
61.30.-v - Liquid crystals.
83.10.Nn - Polymer dynamics.

© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2001