For centuries scientists have dreamt with devices able to mimic the behavior of the biological organs. One of the key aspects of that behavior is the ability to sense the working conditions while actuating. This is due to the electrochemical reactions taking place in the intracellular matrix which provoke the exchange of ions and water with the surroundings. With the view to reaching that potentiality conducting polymers have been widely studied, they are reactive materials constituted by polymeric molecular motors giving multifunctional sensing-actuators whose working principles are the same that those of the biological cells. They are soft materials, containing macromolecules whose conformational movements allow ionic and water exchange. In this work polypyrrole/dodecyl benzene sulfonate (PPy/DBS) films were electrogenerated using different electrochemical parameters giving as a result polymer with different thickness whose mechanical and actuating properties were studied finding relationship between them and with the oxidation state that could lead to the production of conducting polymers with tailor-made properties.
In the dense gel that is the intracellular matrix forming part of living cells electrochemical reactions take place provoking the interchange of ions and water with the surroundings. Systems containing conducting polymers mimic this feature of biological organs. In particular, conducting polymers are being studied as dual sensing-actuating reactive materials giving new multifunctional sensing-actuators, which allow the construction and theoretical description of artificial proprioceptive devices. Here films of polypyrrole/dodecyl benzene sulfonate (PPy-DBS) coating a platinum electrode were submitted to potential sweeps at different sweep rates in order to explore if the polymer reaction senses the working electrochemical conditions. The effective consumed electrical energy per cycle follows a fast decrease when the scan rate increases described by the addition of two exponential sensing functions. Moreover, the variation of the hysteresis from the parallel charge/potential loop with the scan rate is also described by the addition of two exponential functions. In both cases the exponential functions fitting results at low scan rates are related to reaction-driven conformational movements of the polymer chains, being closer to biochemical conformational and allosteric sensors. The second exponential functions fitting results at high scan rates are related to diffusion kinetic control, being closer to present electrochemical sensors.
One of the challenges of modern science is the development of actuators able to sense working conditions while actuation, mimicking the way in which biological organs work. Actuation of those organs includes nervous (electric) pulses dense reactive gels, chemical reactions exchange of ions and solvent. For that purpose, conducting polymers are being widely studied. In this work the properties of self-supported films of the polypyrrole:polyvinilsulfate (PPy/PVS) blend polymer were assessed. X-ray photoelectron spectroscopy (XPS) studies show how during reduction / oxidation the polymer exchanges cations when immersed in a NaClO4 aqueous solution, revealing free positive charges in the electrolytic solution as the driving agents leading to the swelling/shrinking of the polymer. Eventually it is the phenomenon responsible of the actuation of the polymeric motors. Submitting the system to consecutive potential sweeps shows the reaction is really sensing the scan rate used in each cycle revealing that while actuating the system is actually sensing the electrochemical working conditions.
Dual sensing artificial muscles based on conducting polymer are faradaic motors driven by electrochemical reactions, which announce the development of proprioceptive devices. The applicability of different composites has been investigated with the aim to improve the performance. Addition of carbon nanotubes may reduce irreversible reactions. We present the testing of a dual sensing artificial muscle based on a conducting polymer and carbon nanotubes composite. Large bending motions (up to 127 degrees) in aqueous solution and simultaneously sensing abilities of the operation conditions are recorded. The sensing and actuation equations are derived for incorporation into a control system.