Design Criteria of Polymeric Material Interfaces in Fabricating Novel Soft Devices

As technology continues to evolve and diversify, so too does the complexity of soft polymeric devices. It has become increasingly important to develop a set of design criteria for polymer synthesis and fabrication that corresponds to success in electrical engineering and robotics spaces. Polymer material interfaces are widely employed in such devices due to their versatility and excellent characteristics. One goal is to expand the repertoire of polymeric substrates suitable for fabrication of inkjet-printed electronics. This work will focus on strategies for maintaining high conductivity in hydrophilic flexible electronics, while other strategies have been employed previously for hydrophobic substrates. It was found that by pre-treating poly(vinyl alcohol) solutions with trace quantities of an inorganic salt such as magnesium chloride, electronic sensors could be fabricated with high resolution and a low fabrication temperature of 80°C. This demonstrates the importance of the organic-inorganic interfaces in electronic properties. Mg-treated films maintained sheet resistance values of 0.2 Ohms/square, comparable to bulk silver, under both wet and dry conditions, 0-90° curvature, and 0-6% strain.To better understand the design criteria for polymers in soft robotics, a model system of a bilayer composed of an elastic and viscoelastic film was investigated. Bilayer films of SEPS elastomer and butyl rubber demonstrate reversible curvature upon strain-hold-release mechanical cycling. These curvatures and relaxation times can be described with linear and nonlinear spring-dashpot viscoelastic models. Simulations from FEA based on these models showed excellent correlation to the measured values, especially in the generalized Maxwell model. Generalized Maxwell predicts curvature over time with the lowest overall mean absolute scaled error of 0.519, which corresponds to a 4.9% difference from the second lowest error model and 76.8% difference from the highest error model.Based on the elastic/viscoelastic framework, a bilayer capable of responding to moisture was investigated. An interpolymer complex of polyacrylic acid and polyethylene oxide was chosen as the active component. Bilayers of these films melt-pressed onto an elastomeric layer of Tecoflex demonstrated similar curvature as the previously reported elastic/viscoelastic bilayers. PAA-PEO/Tecoflex bilayers can switch reversibly between two stable configurations with both deformation and moisture.