Zane Zondaka

Carbide-derived carbon in polypyrrole changing the elastic modulus with a huge impact on actuation

While carbide-derived carbon (CDC)-based materials have shown stable behavior in ionic electro-chemo-mechanical actuators, the displacement and actuation speed have remained low compared to conducting polymer-based actuators. The goal of this research was to obtain more responsive conducting polymer–CDC composite films and to investigate their linear actuation properties, comparing the stress and strain to those of polypyrrole (PPy) doped with dodecylbenzenesulfonate (DBS−). The PPy–CDC hybrid films were synthesized electrochemically using polyoxometalate (POM) (phosphotungstic acid) to attach charge to the CDC particles for embedding them into the PPy matrix as secondary dopants in addition to DBS−. Cyclic voltammetry and square wave potential steps in electro-chemo-mechanical deformation (ECMD) measurements were performed in aqueous electrolyte solution, showing that the PPy–CDC hybrids had higher strain (12%) and stress (0.6 MPa) than the PPy/DBS films. The new composite was investigated by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy to evaluate the composition of these promising materials.

Electro-chemo-mechanical deformation properties of polypyrrole/dodecylbenzenesulfate linear actuators in aqueous and organic electrolyte

The immobilization of dodecylbenzenesulfonate (DBS−) in polypyrrole (PPy) during electropolymerization is typically expected to lead to cation-driven activity and actuation properties, at least in actuation electrolyte. Here, the complete reversal of the behavior is demonstrated, as the solvent is changed from aqueous to organic while maintaining the same electrolyte – bis(trifluoromethane)sulfonimide lithium salt. Isotonic and isometric electro-chemo-mechanical deformation (ECMD) measurements under cyclic voltammetric and square wave potential measurements yielded strain and stress values in ranges of 9–10% and 0.7–1 MPa, respectively, independent of the solvent. The morphology of PPy/DBS films also changed with the solvent exchange, while elemental analysis confirmed that fluorine atoms from the TFSI− anions can be found only in the PPy/DBS films operated in organic solvent.

Solvent change in polymerization influence linear actuation of polypyrrole carbide-derived carbon films

For actuator applications, conducting polymers are typically deposited at lower temperatures e.g. -20°C, in order to obtain more regular, smooth and ordered films with fewer defects. Clearly, standard aqueous electrolyte solutions cannot be used at these temperatures, and some organic solvents cannot be used, as not all salts are soluble in these. A wellknown approach is to use ethylene glycol: water mixtures (often 50:50 wt%, PPy/CDC(EG:W). The goal of this work is to analyze the role of water in the solution: to compare the linear actuation properties of conducting polymer hybrid films PPy/CDC(EG) polymerized from just ethylene glycol solution and that with 50% water, both at -20°C. Cyclic voltammetry and chronoamperometric electro-chemo-mechanical-deformation (ECMD) measurements were performed to study the linear actuation properties in lithium bis(trifluoromethylsulfonyl)imide in aqueous solution (LiTFSI-aq). Both conductivity and linear actuation strain were found dependent on the solvent in the polymerization solution with ethylene glycol: water the clearly superior solvent choice.

Polypyrrole polymerized in polyethylene oxide: linear actuation in organic and aqueous electrolytes

Embedding polyethylene oxide (PEO) in polypyrrole doped with dodecylbenzenesulfonate (PPy/PEO-DBS) leads to increase linear actuation due to improved ionic conductivity. In this research our goal is to investigate the effect of solvent exchange from aqueous (aq) to propylene carbonate (PC) using same concentration of electrolyte bis(trifluoromethane) sulfonamide lithium (LiTFSI). As previously observed for the case of PPy/DBS films, the actuation direction of PPy/PEO-DBS changed from purely cation-driven in (aqueous) LiTFSI-aq to purely anion driven in (propylene carbonate) LiTFSI-PC. Cyclic voltammetry driven electro-chemo-mechanical-deformation (ECMD) measurements showed that the strain in LiTFSI-PC was more than double than that of aqueous electrolyte consuming only half of the charge density. The diffusion coefficients were determined from the chronoamperometric measurements with higher values found in LiTFSI-PC. Energy dispersive X-Ray spectroscopy and scanning electronic microscopy measurements were performed to characterize the PPy/PEO-DBS films.

Poly-3,4-ethylenedixoythiophene on carbide-derived carbon trilayer: combined linear actuation characterization

Carbide-derived carbon (CDC) based actuators have been typically formulated as trilayer systems and applied in bending displacement. In this work, we want to demonstrate that CDC deposited on glass fiber fabric (CDC-TL) with an additional poly-3.4-ethylenedioxythiophene (PEDOT) layer electropolymerized on top forming a polylayer (expressed as CDC-PEDOT-TL) can be used as a linear actuator. Isotonic and isometric electro-chemo-mechanical deformation (ECMD) measurements in lithium bis(trifluoromethane) sulfonamide propylene carbonate (LiTFSI-PC) were performed, revealing that the CDC expansion at discharging can be found in CDC-PEDOT-TL (main expansion at oxidation of 0.5% strain) in same extent of 0.24 %. The stress found in similar values of 30 kPa for both system. Besides the nearly 5times better conductivity of CDC-PEDOT-TL, the charge density reduce nearly half in comparison to CDC-TL.

Embedded Carbide-derived Carbon (CDC) particles in polypyrrole (PPy) for linear actuator

Conducting polymer linear actuators, for example sodium dodecylbenzenesulfonate (NaDBS) doped polypyrrole (PPy/DBS), have shown moderate strain and stress. The goal of this work was to increase the obtainable strain and stress by adding additional active material to PPy/DBS. In recent year’s carbide-derived carbon (CDC)-based materials have been applied in actuators; however, the obtained displacement and actuation speed has been low comparing to conducting polymer based actuators. In the present work, a CDC-PPy hybrid was synthesized electrochemically and polyoxometalate (POM) – phosphotungstic acid – was used to attach charge to CDC particles. The CDC-POM served in the presence of NaDBS as an additional electrolyte. Cyclic voltammetry and chronopotentiometric electrochemomechanical deformation (ECMD) measurements were performed in Lithium bis(trifluoromethanesulfonyl)- imide (LiTFSI) aqueous electrolyte. The ECMD measurements revealed that the hybrid CDC-PPy material exhibited higher force and strain in comparison to PPy/DBS films. The new material was investigated by scanning electron microscopy (SEM) to evaluate CDC particle embedding in the polymer network.