Contents I. Introduction
Among the thermostatic actuators, the commonly used solution are wax paraffin actuators [1], whose principle of operation is based on the change of state of paraffin from solid to liquid. They are capable of generating large forces, but have the ability to extend only a few percent, they are also quite slow [1, 2, 3]. There were also propositions of actuators based on liquid-gas transformation [4, 5, 6]. A new trend is the creation of composites from a material that changes the phase of state and a flexible matrix [7]. One of the newer such materials is the silicone-ethanol composite [8]. So far, however, it has been mainly studied as a material for use in soft robotics, however its properties suggest that can be used in thermal switches. The principles of actuation of this material are based on phase change transformation. Liquid ethanol after heating and reaching temperature of liquid-vapor transformation start changing state into gas. For atmospheric pressure, this temperature is about 78 degrees Celsius [8, 9]. Vapors of ethanol have much bigger specific volume than liquid, and due to this fact they create pressure on silicon walls causing expansion of material. Also internal pressure inside material rises. The temperature of transformation is dependent for pressure and because of that for continuation of expansion further growth of temperature is necessary. So far, the possibilities of the silicone-ethanol composite have been investigated in terms of the forces and displacements that can be generated. These studies were largely carried out on objects that were modified McKibben actuators. The data presented for unidirectional actuators were usually limited to the presentation of the forces possible to obtain. For samples measuring 50 mm in length and 20 mm in diameter, containing 20% ethanol by volume, a maximum force of 950 N was obtained in the linear operating range at . However, was determined for the proper temperature range in which the material can work, without undergoing rapid degradation. In this range, 130 N was achieved for the tested sample. It was found that the material has the ability to deform by volume of 900%, and it was estimated that it can achieve a one-way elongation of 140%. However, these are values for temperatures higher than [11].
