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Some Advances in Liquid Crystal Elastomers: From Crosslinks Affected Ordering to Carbon Nanoparticles Enabled Actuation

Published online by Cambridge University Press:  15 March 2011

Slobodan Zumer ,
Martin Chambers ,
George Cordoyiannis ,
Heino Finkelmann ,
Zdravko Kutnjak ,
Andrija Lebar ,
Maja Remskar  and
Bostjan Zalar
Slobodan Zumer
Affiliation:
Jozef Stefan Institute, Ljubljana, Slovenia Phyics Department, University of Ljubljana, Ljubljana, Slovenia
Martin Chambers
Affiliation:
Jozef Stefan Institute, Ljubljana, Slovenia
George Cordoyiannis
Affiliation:
Jozef Stefan Institute, Ljubljana, Slovenia Department of Physics and Astronomy, Katholieke Universiteit Leuven, Leuven, Belgium
Heino Finkelmann
Affiliation:
Institute for Macromolecular Chemistry, Albert-Ludwigs-Universität, Freiburg, Germany
Zdravko Kutnjak
Affiliation:
Jozef Stefan Institute, Ljubljana, Slovenia
Andrija Lebar
Affiliation:
Jozef Stefan Institute, Ljubljana, Slovenia Institute for Macromolecular Chemistry, Albert-Ludwigs-Universität, Freiburg, Germany
Maja Remskar
Affiliation:
Jozef Stefan Institute, Ljubljana, Slovenia
Bostjan Zalar
Affiliation:
Jozef Stefan Institute, Ljubljana, Slovenia
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Abstract

Liquid crystal elastomers (LCE) exhibit a combination of elasticity and mesogenic ordering, yielding large thermally stimulated changes in shape. These LCE systems although well characterised, still yield open questions in the nature of how the crosslinking affects the LCE phase transition. Therefore calorimetry and deuteron-nuclear magnetic resonance were used to study the isotropic-nematic phase transition of uniformly ordered LCE. We observed that the density of crosslinkers strongly affects the nematic-isotropic phase transition. The observed spread critical transitions are explained with a dispersion of local mechanical fields that yields a weakly disordered orientational state composed of regions that exhibit temperature profiles of the nematic order parameter ranging from first order to supercritical. On increasing crosslinking density, the predominantly first order thermodynamic response transforms into a predominantly supercritical one.

Additionally, to illustrate the response of these actuating systems, it was demonstrated that a LCE can be electrically heated. The insulating LCE network was reprocessed using conducting nanoparticles dispersed in a solvent with high LCE swelling capability. This results in a low electrical resistivity surface layer of LCE network with a high concentration of conducting nanoparticles. The reprocessing allows the effective resistivity of a LCE film to be reduced from highly insulating values to values useable for electrical actuation. This layer in addition withstands large changes in geometrical shape both in contraction and expansion. Utilizing a resistive “Joule” heating effect, the reprocessed system exhibits an indirect electromechanical effect characterised by a 150% length change that can be cycled for more than 10, 000 times.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1005: Symposium Q – Advances In Photo-Initiated Polymer Processes and Materials , 2007 , 1005-Q04-06
Copyright
Copyright © Materials Research Society 2007

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