Liquid crystalline elastomers as artificial muscles

Tuesday, May 24, 2005 - 4:30pm - 5:00pm
EE/CS 3-180
Patricia Cladis (Advanced Liquid Crystal Technologies, Inc.)
To reduce the very large electric field needed to elicit an electromechanical response from pure liquid crystalline elastomers (LCE), our idea was to apply electric fields to LCEs that had been swollen with low molecular weight liquid crystals.

In the past three decades, swelling properties of isotropic polymer gels in isotropic solvents have attracted much attention and their physical mechanisms are now well understood [1]. On the other hand, a liquid crystal elastomer (LCE), an anisotropic gel, has been recently synthesized, for which swelling properties in an anisotropic solvent such as low molecular weight liquid crystals (LMWLCs) are different from the well-known isotropic case [2]. In particular, we found that the swelling properties and temperature behavior (thermomechanical property) of volume changes were also anisotropic.

Understanding the physical mechanisms responsible for thermomechanical effects in LCEs is important to make functional materials that can work as, e.g., temperature-driven actuators or artificial muscles [3]. Another useful property for them would be as devices that changed their shape in applied electric fields rather than temperature, i.e. their electromechanical effect. In current dry LCEs, however, fields of about 1V/micron are required to induce electromechanical effects.

In contrast to this, the electric field response of LMWLCs in the parallel plate geometry is a well-known cooperative phenomena, i.e. is a voltage effect, not a field effect as it is for nematic elastomers. As a result, LCEs swollen with nematic LMWLCs could be a good candidate to observe measurable shape changes at low voltages. Indeed, only a small voltage (about 1V) is required to change the orientation of nematic LMWLCs. Should there be a strong enough coupling between the mesogenic side-chains of the LCE and LMWLC molecules, the question is, can the low voltage response of LMWLCs be harnessed to induce reorientation effects in the tethered LCE side chains to obtain measurable shape changes at low voltages? Our brief answer is yes. However, while the voltages are small, comparable to that of LMWLCs, the reorientation effect is also small [4].

In this talk, I will give some snapshots of our experimental results to date [2,4].

1. A. Onuki, Adv. Poly. Sci., 109, 63 (1993).

2. Y. Yusuf, Y. Ono, Y. Sumisaki, P. E. Cladis, H. R. Brand, H. Finkelmann, and S. Kai, Phys. Rev. E, 69, 021710 (2004).

3. P. G. de Gennes, M. Hubert, and R. Kant, Macromol. Symp., 113, 39 (1997); M. Hubert, R. Kant, and P. G. de Gennes, J. Phy. I France, 7, 909 (1997).

4. Y. Yusuf, J-H. Huh, P.E. Cladis, H.R. Brand, H. Finkelmann, S. Kai, Phys. Rev. E. (in press).