Advances in Science and Technology Vol. 61

Abstract: Since the Stone Age, people have tried to reproduce the human appearance, functions, and intelligence using art and technology. Any aspect that represents our physical and intellectual being has been a subject of copying, mimicking and inspiration. Recent surges in technology advances led to the emergence of increasingly more realistic humanlike robots and simulations. Making such robots is part of the field of biologically inspired technologies - also known as biomimetics - and it involves developing engineered systems that exhibit the appearance and behavior of biological systems. Robots with selectable characteristics and personality that are customized to our needs and with self-learning capability may become our household appliance or even companion and they may be used to perform hard to do and complex tasks. In enabling this technology such elements as artificial intelligence, muscles, vision, skin and others are increasingly improved. In this paper, making humanlike robots will be described with focus on the use of artificial muscles as the enabling technology and the related challenges.

Abstract: Interpenetrating polymer networks (IPNs) have been developed for many years leading to materials with controlled properties. When an electronic conducting polymer (ECP) is incorporated into an IPN, this one becomes a conducting IPN (CIPN). The synthetic pathway ensures a non homogeneous dispersion of the ECP through the IPN thickness of the material. The system is thus similar to a layered one with the advantage that the intimate combination of the three polymers needs no adhesive interface. The last step in making the CIPN into an actuator is to ensure the ionic conductivity by incorporation of an ionic salt. The highest ionic conductivity through the IPN matrix is necessary in order to ensure the best actuation. The chosen salt is an ionic liquid, i.e. 1-ethyl-3- methylimidazolium bis(trifluoromethylsulfonyl)imide (EMImTFSI). Based on IPN architectures electrochemical actuators have been designed and actuation in open air has been characterized.

Abstract: One of the key factors to obtain large displacements and high efficiency with dielectric electroactive polymer (DEAPs) actuators is to have compliant electrodes. Attempts to scale DEAPs down to the mm or micrometer range have encountered major difficulties, mostly due to the challenge of micropatterning sufficiently compliant electrodes. Simply evaporating or sputtering thin metallic films on elastomer membranes produces DEAPs whose stiffness is dominated by the metallic film. Low energy metal ion implantation for fabricating compliant electrodes in DEAPs presents several advantages: a) it is clean to work with, b) it does not add thick passive layers, and c) it can be easily patterned. We use this technology to fabricate DEAPs micro-actuators whose relative displacement is the same as for macro-scale DEAPs. With transmission electron microscope (TEM) we observed the formation of metallic clusters within the elastomer (PDMS) matrix, forming a nano-composite. We focus our studies on relating the properties of this nano-composite to the implantation parameters. We identified the optimal implantation parameters for which an implanted electrode presents an exceptional combination of high electrical conductivity and low compliance.

Abstract: Conducting polymer actuators are of interest in applications where low voltage and high work density are beneficial. These actuators are not particularly fast however, with time constants normally being greater than 1 second. Strain in these actuators is proportional to charge, with the rate of charging being found to limit the speed of actuation. This rate of charging is in turn limited by a number of factors, the dominant factor depending on the actuator and cell geometry, the potential range, the composition and the timescale of interest. Mechanisms that slow response can be as simple as the RC charging time arising from the actuator capacitance and the series resistances of the electrolyte and the contacts, or may involve polymer electronic or ionic conductivities, which can in turn be functions of potential. Diffusion can also be a factor. An approach is presented to help estimate the relative magnitudes of these rate limiting factors, thereby enabling actuator designs to evaluated and optimized for a given application. The general approach discussed is also useful for analyzing rate limits in carbon nanotube actuators and other related technologies.

Abstract: The insertion of inorganic nanoparticles and nanowires in a liquid crystalline elastomeric environment is here investigated. The combination of ferroelectric and conductive properties of the nanomaterials with the thermo-mechanical and shape memory response of liquid single crystal elastomers based on polysiloxane is indeed very promising for new technological applications, such as electroactive actuators. In this work the preparation and physical-chemical properties of new composites are presented and discussed in comparison with those of standard liquid single crystal elastomers (LSCEs). In particular, we are reporting the preliminary results of new composites including either lead titanate nanoparticles or molibdene oxide nanowires, having different electric and conductive properties.

Abstract: Gel is a fascinating material for its unique properties, such as phase-transition, chemomechanical behavior, stimuli-responsiveness, low surface sliding friction, and for its possible wide application in many industry fields. Recently, hydrogels have drawn special attraction in biological field due to its possible applications as soft man-made tissues. However, conventional hydrogels, especially polyelectrolyte gels, are mechanically too weak to be practically used in any stress or strain bearing applications. Inspired by the structure of articular cartilage, we discovered a general method to obtain very strong polyelectrolyte hydrogels containing 60-90% water by inducing a double-network (DN) structure for various combinations of hydrophilic polymers. The soft and wet gel materials with both a high strength and an extremely low surface friction would find wide applications not only in industry but also in biomedical field, for example, as substitutes of articular cartilage or other bio-tissues.

Abstract: The need for high electric fields to drive dielectric elastomers is still retaining their diffusion as actuators in some areas of potential application, as in the case of biomedical disciplines. The development of new materials offering superior electromechanical properties is thus an essential requirement in order to effectively reduce the driving fields. In this light, the present work is aimed to enhance the electromechanical properties of two silicone and polyurethane based dielectric elastomers, both by making particulate composites with high-permittivity ceramic fillers, and by blending with a highly polarisable polymeric phase. Due to a consequent worsening of the mechanical properties, pure composite architectures yielded only limited results on the overall electromechanical response. With the blend approach, instead, both an increase of the dielectric permittivity and an unexpected reduction of the tensile elastic modulus were observed, leading to an overall increase of the electromechanical response. In any case, a key role appears to be played by the nature and intensity of polarisation phenomena arising at interfaces between different phases.

Abstract: In this work, we report the development of “one piece” electrochemical actuator fibers, presenting linear deformations, and working in open-air. The hollow fiber shaped actuators are synthesized as three components Interpenetrating Polymer Network (IPN). The electronic conducting polymer (ECP), poly(3,4-ethylenedioxythiophene) (PEDOT), is embedded in a hollow fiber shape matrix working as two ECP concentric electrodes. The host matrix which presents an IPN type architecture is composed of two poly(ethylene oxide) networks, crosslinked in the presence of each other. Strains up to 3 % and forces between 50 and 300 mN are realized in a two electrodes configuration, in open-air.