Many artificial muscles can only operate in water, as they must soak and release water to change dimensions. Alternatively, liquid crystal elastomer (LCE) materials, are artificial muscles that only require internal rearrangement. They exhibit reversible uniaxial changes with strains of 20-500% and stresses of 10-100 kPa: falling exactly into the dynamic range of a biological muscle. In addition, LCEs exhibit little to no fatigue over thousands of actuation cycles.
However, the process of synthesizing these materials is complicated, involving irradiation while mechanically stretching the sample. Such a process in difficult to control and limits muscles to being large thin films.
Now, researchers from the Active and Intelligent Materials (AIM) lab at the University of Cambridge, in collaboration with the Cavendish Laboratory have simultaneously solved several problems that limit the applications of LCEs [Jean E. Marshall, Sarah Gallagher, Eugene M. Terentjev, and Stoyan K. Smoukov, J. Am. Chem. Soc., 2014, 136 (1), pp 474–479, doi: 10.1021/ja410930g]. First, they lowered the operating temperature from 80-120 °C down to 58 °C by introducing co-monomer molecules which disrupt the molecular order. They also discovered a way to “grip” micron-sized particles by embedding them in a matrix, and stretching the matrix instead.
But for the researchers, the most interesting aspect of the work has been “fitting a square peg in a round hole”, but on the molecular scale. By confining the material to spaces less than 20 microns wide, the alignment of the molecules can be frozen, even at temperatures above the melting point. This greatly simplifies the synthesis procedure and suggests novel ways that molecules can be manipulated using confinement effects.
This story is reprinted from material from the University of Cambridge, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.