Advances in Science and Technology Vol. 79

Abstract: We have fabricated a prototype model artificial muscle that drives model phalanges in water with ion polymer metal compound (IPMC) which generates relatively large displacement with fast response but generates relatively small force. We have developed IPMC of greater thickness of up to 600 µm than conventional Nafion 117 based IPMC of 200 µm which enabled to generate greater force. In fabricating IPMC Nafion R-1100 resin was heat-pressed at 185 °C with 20-30 MPa. The thickness of IPMC could be adjusted by changing the amount of resin, pressure, and time to heat-press. Fabricated IPMC was then cut in shapes and an electrode was attached on the surface of IPMC. The device was used as an artificial muscle type actuator which was fabricated in a shape that bridges two conjoining bones, and controls opening angle of the bones that mimics contraction and expansion motion of the muscle. Bipolar power supply and function generators were used to drive IPMC membranes attached to the model phalanges.

Abstract: This contribution considers an actuator based on Electroactive Polymers (EAPs) which is used for constructional elements with controllable stiffness. The actuator consists of a Danfoss PolyPower EAP-foil and a supporting structure which applies the necessary pre-straining force to the foil. Usually, such structures have a constant spring stiffness which strongly limits the actuation range. The novel actuator shows a highly nonlinear spring stiffness for pre-straining the foil. Therefore, the pre-straining force is nearly constant all over the entire actuation range. This behavior can be used to double the possible actuation range. Such structures are suitable to be used in construction elements with variable stiffness. The contribution shows the basic function of this actuator and its capabilities for the application in new smart, self-sensing and self-controlling composite materials for lightweight constructions. The theoretical background of highly nonlinear spring stiffness is discussed and transferred to the developed structures. The theoretical calculations are based on analytic calculations and finite element analyses and are verified by experimental set-ups consisting of different actuators both with constant and highly nonlinear pre-straining spring constant.

Abstract: The combination of nanoparticles and conducting polymers, known as hybrid conducting nanocomposites, is a new emerging field. The combination of conductive polymers, such as polyaniline (PANI), with conductive carbon nanotubes (CNTs) has already shown some synergistic properties. As a consequence, they have a variety of applications, such as sensors, actuators, touch screens, etc.. Usually PANI and CNTs are combined by using electrochemical synthesis starting with the monomer aniline. In this work PANI-CNTs nanocomposite films were obtained by using different combinations of two methods, Electrochemical Deposition (ELD) and Electrophoretic Deposition (EPD). The samples prepared by using these combined methods were compared with the material prepared by the usual electrochemical synthesis. Therefore, all the films so prepared were characterised and their electrochemical properties were investigated, particularly for evaluating their use as supercapacitor components.

Abstract: Free-standing films made of poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT/PSS) were prepared by casting water dispersion of its colloidal particles. Specific surface area, water vapor sorption, and electro-active polymer actuating behavior of the resulting films were investigated by means of sorption isotherm, and electromechanical analysis. It was found that the non-porous PEDOT/PSS film, having a specific surface area of 0.13 m2/g, sorbed water vapor of 1080 cm3(STP)/g, corresponding to 87 wt%, at relative water vapor pressure of 0.95. A temperature rise from 25 to 40 °C lowered sorption degree, indicative of an exothermic process, where isosteric heat of sorption decreased with increasing water vapor sorption and the value reached 43.9 kJ/mol, being consistent with the heat of water condensation (44 kJ/mol). Upon application of 10 V, the film underwent contraction of 2.4% in air at 50% relative humidity (RH) which significantly increased to 4.5% at 90% RH. The principle lay in desorption of water vapor sorbed in the film due to Joule heating, where electric field was capable of controlling the equilibrium of water vapor sorption.

Abstract: The paper presents a dynamic measurement method of the distribution of foot pressure exerted on the ground by a four-point shoe insole, developed by authors, which can be placed in any sport footwear. The value of pressure was measured on the heel, medial midfoot, metatarsal, and great toe by recording values of a generated voltage by sensors which were made of piezoelectric polymer PVDF film 110 µm thick with printed silver electrodes. As confirmed by scanning microscope studies, the foil applied in the sensors is semi-crystalline. The shoe measurement insert consists of two polyester films without piezoelectric properties between them, electroactive polymer sensors were placed. The films were glued together. To match the measuring circuit to the sensors used, two circuits were tested, a voltage measuring circuit with an input resistance of above 10¹² Ω (open circuit), and a charge measuring circuit (shorted circuit). The charge measuring circuits with the RC high-pass filter, which attenuates the slow-changing pyroelectric signal was selected as it ensures the desired measurement accuracy. As presented in the paper, as PVDF sensors are very sensitive to any mechanical deformation, it is important to properly design the shoe insole to ensure its correct use during pressure distribution measurements. The measuring system developed by the authors, allows testing of foot pathology for any length of time in a dynamic way.