The project aims to develop functional elastomers with crosslinking polymer networks that can serve as touch and strain sensors with very good elastic properties with several hundred percent elongation at break values and simultaneously keeping stiffness or the initial modulus even in kPa range (Fig. 1). In literature various publications related with the development of functional parts (sensors, actuators, main body) of soft robotic system can be found but most of them are either silicone or acrylic based elastomer composites where the mechanical performance and long-term reliabilities of the sensors are remained under doubt. For example, even though, plenty of literature can be found on elastomeric strain sensors by the use of conducting carbon particles (graphene, carbon nanotubes etc.), the viscoelastic (time/frequency and temperature) properties of the elastomers are not considered in details. Typical viscoelastic properties like creeping, stress relaxation, fatigue to failure, hysteresis etc. may lead to non-reproducible performance and properties of the sensors. Much deeper insights are therefore necessary to understand the dynamic piezoresistivity of the conductive rubber composite systems under dynamic loading and unloading conditions. This would then be the first step in developing a dynamic rubber based sensor for soft robotic arms that can detect and yield information about the motion, deformation, performance and lifetime.
Thus, the proposed project will be devoted to develop sensor systems which include soft and highly stretchable strain sensors, and triboelectric based soft touch sensors by the utilizing commercial rubbers like NR, SBR, nitrile rubber(NBR), polychloroprene rubber(CR)etc. besides silicone rubber. A schematic presentation of a part of pneumatically driven soft robot is shown in Fig. 1 where triboelectric touch as well as long range strain sensors are described. The elastomers will be comprised of commercially available high-performance rubbers like SBR, BR (butadiene rubber) or even NR. The functionality of those elastomers will be impregnated by the use of functional fillers, and proper selection of raw materials, following suitable processing and fabrication protocols. Studies will be carried out on the development and preparation of soft functional elastomers by the exploitation of our strong competences in the design and tailored preparation of elastomeric substratesand the final performance will be optimized in close cooperation with our other cooperation partners.
Fig. 1: A sketch of a part of soft robots explains the fabrication with different types of functional elastomer that can offer touch and strain sensitivity simultaneously. The embedded stress-strain curves are describing the softness nature of natural rubber compounds which is crosslinked by standard sulphur curing procedure. The Young’s modulus of such plasticized natural rubber can be as low as ~500 kPa which is very similar to the soft silicone rubber.