Artificial muscles represent a class of biologically inspired materials that can reversibly contract and expand by application of an external stimuli, such as temperature [1], pressure [2], voltage [3], or current [4]. By potential conversion of muscle's mechanical deformation to useful work or electricity, it can be used as a means for energy storage as well. Recently, artificial muscles have become a popular topic in both academic and industrial fields, where search for innovative actuation devices based on various mechanisms have been initiated and advanced materials with superior performances in many aspects compared to those of natural muscles have been developed. Among other polymers, which can serve as a basis for constructing artificial muscles, silicon rubber possesses many advantages. This elastomer is relatively cheap and possesses useful properties, such as ease manufacturing and shaping, non-reactivity with most chemicals, stability, good resistance to extreme temperatures, ability to operate normally from −100 to 300 °C, biocompatibility, which allows one to use it in many medical applications where contact with skin, water, blood, active ingredients, etc., is needed. At the same time, silicone rubber has low tensile strength, poor wear and tear wear properties and is too soft for some mechanical applications, which stimulates development of new composites that overcome these drawbacks.

The objective of this work is to demonstrate a novel prototype for a composite artificial muscle where specific filler is used to improve its mechanical and thermal conducting properties. Specifically, the muscle is based on the composite of a silicon rubber and a carbon fiber. The latter serves for reinforcement of the mechanical strength of the elastomer and improvement of its thermal conductivity properties for thermomechanical applications.

First, the elastomer is shown to be able to lift the cargo which is more than one order of magnitude higher than the weight of the sample itself (Fig. 1a). In this sense, the muscle can be used to store the mechanical energy. Second, our studies show how the extent and orientation of the carbon fiber load in the polymer sample influences the rate and extent of the sample deformation. Particularly, it is demonstrated that the relative deformation of the sample can reach up to 5% upon heating to 70-80 0C. We also demonstrate that depending on the fiber orientation in the sample one can control the sample rigidity and thus either to suppress or to promote the sample deformation (Fig. 1b). Suppression of the sample deformation is due to increasing mechanical strength, whereas its promotion is due to improved thermal conductivity of the composite sample. A simple control of thermomechanical properties of the muscle and relatively cheap material it is composed of makes it perspective for applications in such fields as collection and storage of thermal energy.