Rheology of liquid crystalline elastomers in their isotropic and smectic Astate

Citation
J. Weilepp et al., Rheology of liquid crystalline elastomers in their isotropic and smectic Astate, MACROMOLEC, 32(14), 1999, pp. 4566-4574
Citations number
38
Categorie Soggetti
Organic Chemistry/Polymer Science
Journal title
MACROMOLECULES
ISSN journal
00249297 → ACNP
Volume
32
Issue
14
Year of publication
1999
Pages
4566 - 4574
Database
ISI
SICI code
0024-9297(19990713)32:14<4566:ROLCEI>2.0.ZU;2-9
Abstract
The dynamics of two different side-chain liquid crystalline elastomers (SCL CE) exhibiting a smectic A phase is investigated by low-frequency shear and compression experiments. We find that both the isotropic and the smectic A phase have their own characteristic viscoelastic behavior,:which seems to be independent of the compound under investigation and thus universal. The relaxation in-the isotropic phase shows a distribution of relaxation times, which gives rise to a scaling law of the elastic moduli with an exponent o f 0.5. The viscoelastic response in the smectic A phase,however, exhibits a much broader spectrum of relaxation times containing very long-lived modes . It appears that there exists a low-frequency scaling law with an exponent of 0.3 characterizing the smectic A phase. We propose that this result ste ms from a transient smectic network with a very long lifetime that was set up by the smectic domains. At the phase transition, this transient smectic network disappears, which leads to a sharp decrease of the dynamic shear as well as the compression modulus.