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In this article, it is proposed that a membrane with tunable ionic conductivity can be used as a separator between the electrodes of a supercapacitor to both allow normal charge/discharge operation and minimize self-discharge when not in use. It is shown that the redox active conducting polymer PPy(DBS), when polymerized on a porous substrate, will span across the pores of the membrane. PPy(DBS) is also shown to function as an ionic redox transistor, in which the transmembrane ionic conductivity of the polymer membrane is a function of its redox state. The PPy(DBS) ionic redox transistor is applied between the electrodes in a supercapacitor as a smart membrane separator. It is demonstrated that the maximum tunable ionic conductivity of the smart membrane separator is comparable in operation to an industry standard separator at maximum ionic conductivity, with a self-discharge leakage current of ∼0.12mA/cm2 at 1V. The minimum tunable ionic conductivity of the smart membrane separator is shown to decrease the supercapacitor self-discharge when not in use by a factor of 10, with a leakage current of 0.012mA/cm2 at 1V. This range of tunable ionic conductivity could lead to the emergence of redox transistor batteries with high energy density and low self-discharge for short and long-term storage applications.

Ionomers are a class of polymers which contain a small fraction of charged groups in the polymer backbone. These ionic groups aggregate (termed ionic aggregates) to form temporary cross-links that break apart over the ionic dissociation temperature and re-aggregate on cooling, influencing the mechanical properties of these polymers. In addition to enhanced mechanical properties, some ionomers also exhibit self-healing behavior. The self-healing behavior is a consequence of weakly bonded ionic aggregates breaking apart and re-aggregating after puncture or a ballistic impact. The structure and properties of ionomers have been studied over the last several decades; however, there is a lack of understanding of the influence of an electrostatic field on ionic aggregate morphology. Characterizing the effect of temperature and electric field on the formation and structure of these ionic aggregates will lead to preparation of ionomers with enhanced structural properties. This work focuses on Surlyn 8940 which a poly-ethylene methacryclic acid co-polymer in which a fraction of the carboxylic acid is terminated by sodium. In this work, Surlyn is thermoelectrically processed over its ionic dissociation temperature in the presence of a strong electrostatic field. Thermal studies are performed on the ionomer to study the effect of the thermoelectric processing. It is shown that the application of a thermoelectric field leads to increase in the ionic aggregate order in these materials and reduction in crystal size distribution. Thermal Analysis is performed using a Differential Scanning Calorimeter and the resulting thermogram analysis shows that thermoelectric processing increases the peak temperature and onset temperature of melting by 4 C and 20 C respectively. The peak width at half maximum of the melting endotherm is reduced by 10 C due to thermoelectric processing. This serves as a measure of the increased crystallinity. A parametric study on the effect of field duration and field strength is also performed.

Real time measurement of time-correlated ion transport and volumetric changes in electroactive materials is necessary to understand and model mechanoelectrochemistry. Reversible reduction and oxidation of soft electroactive materials such as conducting polymers result in the deformation of the material due to ion transport into and out of the polymer backbone. In cells, ion transport and volumetric expansion are collectively responsible for homeostasis that is essential for life functions and hence, mechanoelectrochemistry of cells is essential to understand cell and developmental biology. The characterization methods required to investigate mechanoelectrochemistry require nanoscale spatial resolution for the imaging of a redox active site in a polymer or a small group of transmembrane proteins in a single cell. Towards this goal, we present an imaging technique using scanning electrochemical microscopy (SECM) hardware with shear-force (SF) feedback for high bandwidth mechanoelectrochemistry characterization. In this proceedings article, we demonstrate this technique referred to as surface-tracked scanning electrochemical microscopy technique (ST-SECM) that is realized by measuring the structural feedback of the glass electrode to position the electrode in 10s of nanometers above the surface of a polypyrrole membrane doped with dodecylbenzenesulfonate (PPy(DBS)). Two ultra-microelectrodes of controlled dimensions (of 20 μm and 30 μm glass diameter) were fabricated using a hydrofluoric acid etching technique and were used to generate a spatially correlated ion storage map of PPy(DBS). We compare the developed technique to a three-dimensional discrete scan over the surface and show that a ST-SECM technique produces a higher resolution and takes approximately 200 fewer minutes as compared to the conventional technique.

Conducting polymers undergo volumetric expansion through redox-mediated ion exchange with an electrolyte under an applied electrical field. The resulting ion transport processes control the conformational relaxation of the polymer backbone and regulate the generated stress and strain. In this paper, a constitutive model has been developed from first principles to examine coupled chemomechanical response for a polypyrrole-based conducting polymer actuator. The mechanics of charge ingress and egress is used to compute chemomechanical coupling coefficient of a polypyrrole doped with dodecylbenzene sulfonate (PPy(DBS)) cantilever actuator and the resulting values are compared with experimental data over a range of sodium chloride (NaCl) electrolyte concentrations from 1 mM to 1 M. The model predicts concentration dependent strain and chemomechanical coupling coefficient for the actuator and it is observed that the strain generated by the actuator saturates above a certain value of cation concentration in the electrolyte. The maximum strain developed by the conducting polymer is found to be dependent on the volume of the PPy(DBS) layer and it is estimated that the chemomechanical coupling coefficient varies between 0.016 and 0.023 dm 3 /mole as a function of electrolyte concentration (0.001 to 1 M). A mechanistic approach to interpret the results from the model and experiments is proposed and correlations between structure (number of redox sites in the polymer, packing density), input (electrolyte concentration, electrical potential), output (strain) and constitutive relation (chemomechanical coupling coefficient) are derived.

Self-healing materials science has seen significant advances in the last decade. Recent efforts have demonstrated healing in polymeric materials through chemical reaction, thermal treatment, and ultraviolet irradiation. The existing technology for healing polymeric materials through the aforementioned mechanisms produces an irreversible change in the material and makes it unsuitable for subsequent healing cycles. To overcome these disadvantages, we demonstrate a new composite self-healing material made from an ionomer (Surlyn) and carbon fiber that can sustain damage from medium-velocity impact and heal from the energy of the impact. Furthermore, the carbon fiber embedded in the polymer matrix results in resistive heating of the polymer matrix locally, melts the ionomer matrix around the damage, and heals the material at the damaged location. This paper presents methods to melt-process Surlyn with carbon fiber and demonstrates healing in the material through medium-velocity impact tests, resistive heating, and imaging through electron and optical microscopy. A new metric for quantifying self-healing in the sample, called width-heal ratio, is developed, and we report that the Surlyn-carbon fiber-based material under an optimal rate of heating and at the correct temperature has a width-heal ratio of >0.9, thereby demonstrating complete recovery from the damage.

Ionomers are polymers containing a small fraction of charged groups in their polymer backbone. These ionic groups link together to form ionic aggregates which act as temporary cross-links. On heating over the ionic dissociation temperature, these ionic aggregates become mobile in the melt and reaggregate upon cooling. The structure and dynamic behavior of these ionic aggregates gives rise to interesting mechanical and functional properties of the ionomers. Thermal processing of ionomers leads to secondary equilibration of these ionic aggregates. We study this phenomenon of secondary equilibration on application of a thermo-electric field where an electrostatic field is maintained over the ionomer melt. The end goal is to achieve control over the size and distribution of the ionic aggregates by means of an external electric field. The characterization techniques utilized to study the onset of secondary equilibration are UV-Vis Spectroscopy, Differential Scanning Calorimetry, Fourier Transfer Infrared Spectroscopy and Attenuated Total Reflectance analysis. The results indicate that the phenomenon of secondary equilibration is present under the application of a thermoelectric field as indicated by change in spectral and thermal data. A fundamental understanding of the secondary equilibration phenomenon and eventual prevention of the onset of secondary equilibration will lead to long term control of the ionic aggregates by means of an external electric field which will improve the function and utility of these ionomeric materials.

Mechanoelectrochemistry is the study of elastic and plastic deformation of materials during reversible reduction and oxidation processes. In this article, we introduce shear-force tracking as a method to dynamically measure mechanical (strain), chemical (ion transport), and electrical (applied redox potentials) responses of the conducting polymer polypyrrole (PPy) during redox reactions. This tracking technique uses a control algorithm to maintain a set distance between a ultramicroelectrode (UME) tip and a surface via shear-force regulation. Due to the sensitivity of shear-force signals in the near field of substrate surfaces, a significantly improved signal to noise ratio (20 : 1) is possible and allows for nanoscale measurement of redox events. Chemomechanical coupling (the ratio of ion transport to resultant extensional actuation) is calculated for PPy-based membranes of various thicknesses based on a mechanistic interpretation of charge storage in redox active conducting polymers. The measured dynamic response demonstrates that chemomechanical coupling is not a constant, as assumed in literature, but is dependent on the polymers state of charge and the direction (ingress/egress) of ion transport.

Conducting polymers undergo volumetric deformations due to ingress/egress of counter-ions and solvent molecules during electrochemical reduction/oxidation. A precise measurement of volumetric deformations (as extensional strain) has been elusive due to lack of experimental methods and hence, different mathematical models make simplifying assumptions in attributing the strain to various transported species. Recently, an investigation into static and dynamic mechanoelectrochemistry of polypyrrole doped with dodecylbenzenesulfonate (PPy(DBS)) has provided morphology-dependent strain data for PPy(DBS) and can be used to precisely attribute volumetric strain of PPy(DBS) to various components that move into and out of the polymer. To address the longstanding need for a mass transport based mechanics model, we present a morphology-dependent mathematical framework that attributes the strain during electrochemical reduction/oxidation of PPy(DBS) to cations and solvent (water) molecules. This model builds upon a chemomechanical constitutive model for conducting polymers and combines it with measured strain to derive fundamental structure-property-function relationships in PPy(DBS). The polymer's morphology is represented by macroscopic porosity in the oxidized state and it is observed that the porosity of the polymer in the oxidized state decreases linearly with electrochemical deposition charge density (C cm−2). The osmotic pressure due to ion and water transport is found to be inversely proportional to porosity of the polymer, and number of water molecules transported appear to be governed by the interplay between osmotic pressure and compliance of the film. These results are anticipated to serve as guidelines in the design of robust biomedical devices and energy storage materials using PPy(DBS) and other conducting polymers in aqueous/organic solvents.

Recent studies of polypyrrole (PPy) electrodes have been increasing the interfacial surface area in order to increase electrochemical performance. We present a novel method of electropolymerizing PPy doped with dodecylbenzenesulfonate (DBS) referred to as biotemplating. A biotemplated conducting polymer utilizes phospholipid vesicles in order to form a three dimensional structure with a sponge-like shape. The vesicles, measuring 1–2 μm in diameter, are added in situ with the polymerization solution. They become enveloped while maintaining their structure during electropolymerization of PPy(DBS). The result of this structure is a significant increase in surface area compared to current techniques. There are several advantages in using biotemplated conducting polymers as battery electrodes. Compared to a planar PPy(DBS) membrane, biotemplated PPy(DBS) membranes have a roughly 50% increased storage capacity. There is an expected reduction in volumetric expansion during ion ingress/egress into the polymer backbone. This reduction would result in decreased fatigue loading and improving cyclability. Further, biotemplated PPy(DBS) membranes can be fabricated into thin structures with increased flexibility, allowing them to be rolled into various packaging sizes. In this article, the charge density of a biotemplated PPy(DBS) membrane as a function of charging and discharging currents is compared to a planar PPy(DBS) membrane. The structural enhancement offers systemic advantages by providing higher volumetric energy density and decreased fatigue loading for applications involving conducting polymer electrodes.Copyright © 2013 by ASME

Conducting polymers undergo volumetric expansion through redox-mediated ion exchange with its electrolytic environment. The ion transport processes resulting from an applied electrical field controls the conformational relaxation in conducting polymer and regulates the generated stress and strain. In the last two decades, significant contributions from various groups have resulted in methods to fabricate, model and characterize the mechanical response of conducting polymer actuators in bending mode. An alternating electrical field applied to the polymer electrolyte interface produces the mechanical response in the polymer. The electrical energy applied to the polymer is used by the electrochemical reaction in the polymer backbone, for ion transport at the electrolyte-polymer interface and for conformational changes to the polymer. Due to the advances in polymer synthesis, there are multitudes of polymer-dopant combinations used to design an actuator. Over the last decade, polypyrrole (PPy) has evolved to be the most common conducting polymer actuator. Thin sheets of polymer are electrodeposited on to a substrate, doped with dodecylbezenesulfonate (DBS-) and microfabricated into a hermetic, air operated cantilever actuator. The electrical energy applied across the thickness of the polymer is expended by the electrochemical interactions at the polymer-electrolyte interface, ion transport and electrostatic interactions of the backbone. The widely adopted model for designing actuators is the electrochemically stimulated conformational relaxation (ESCR) model. Despite these advances, there have been very few investigations into the development of a constitutive model for conducting polymers that represent the input-output relation for chemoelectromechanical energy conversion. On one hand, dynamic models of conducting polymers use multiphysics-based non-linear models that are computationally intensive and not scalable for complicated geometries. On the other, empirical models that represent the chemomechanical coupling in conducting polymers present an over-simplified approach and lack the scientific rigor in predicting the mechanical response. In order to address these limitations and to develop a constitutive model for conducting polymers, its coupled chemomechanical response and material degradation with time, we have developed a constitutive model for polypyrrole-based conducting polymer actuator. The constitutive model is applied to a micron-scale conducting polymer actuator and coupling coefficients are expressed using a mechanistic representation of coupling in polypyrrole (dodecylbenzenesulfonate) [PPy(DBS)].Copyright © 2013 by ASME

Enzymes have evolved over hundreds of years through changes in ecosystems (climate, atmosphere, hydrology, etc). The evolutionary changes driven by the need to survive has led to enzymes with diverse functionality such as reduction of carbon dioxide and methane to other forms of carbon, fixation of nitrogen, and high temperature biochemical processes. While these enzymes have useful properties, engineering a scalable cell-free system with these enzymes will be useful for stable production of desired products without involving the vagaries of cellular metabolism. This article presents various approaches to incorporate ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) in a conducting polymer (polypyrrole (PPy)) doped with a bulky anion (dodecylbenzenesulfonate (DBS)) in an effort to create functional devices for the conversion of carbon dioxide into precursors for high-value chemicals. We demonstrate that the tailored device creates an environment where the enzyme can retain its function while being protected from denaturing conditions. It is envisioned that the 3-PGA produced by RuBisCO will be converted into value-added products.

Conducting polymers are ionic active materials that can perform electro-chemo-mechanical work through redox reactions. The electro-chemo-mechanical coupling in these materials has been successfully applied to develop various application platforms (actuation systems, sensor elements and energy storage devices (super capacitors, battery electrodes)). Similarly, bioderived membranes are ionic active materials that have been demonstrated as actuators, sensors and energy harvesting devices. Bioderived membranes offer significant advantages over synthetic ionic active materials in energy conversion and the scientific community has put forward various system level concepts for application in engineering applications. The biological origins of these material systems and their subsequent mechanical, electrical and thermal properties have served as a key deterrent in applications. This article proposes a novel architecture that combines a conducting polymer and a bioderived membrane into an integrated material system in which the charge gradients generated from a biochemical reaction is stored and released in the conducting polymer through redox reactions. This paper discusses the fabrication and topographical characterization of the integrated bioderived-conducting polymer membrane nanostructures. The prototype comprises of an organized array of fluid-filled three-dimensional containers with an integrated membrane shell that performs energy conversion and storage owing to its multi-functional microstructure. The bioderived membrane is self-assembled into a hollow spherical container from synthetic membranes or bilayer lipid membranes with proteins and the conducting polymer membrane forms a wrapper around this container resulting in a three-dimensional assembly.Copyright © 2012 by ASME

Biological processes and electromechanical function in ionic polymers share ion transport as the fundamental processes for sensing, actuation and energy harvesting. Inspired by the similarity in protein-bound cell membranes and polypyrrole membrane (an ionic polymer), our group is developing a hybrid device that provides the template for integrating biology and electronics. The integrated device, referred to as a bio-derived ionic transistor (BIT), consists of a bilayer lipid membrane (BLM) formed on a polypyrrole membrane and has two inputs that regulates the output of the device. This proceedings article will discuss the constructional features of proposed actuator, fabrication procedure of a prototype actuator and discuss a modeling framework for analyzing the dynamics of the ionic response.

A new fabrication system for Ionic Polymer Metallic Composites (IPMC) entitled Micro Deposition Method(MDM) is introduced. The tolerances in prototyping IPMC’s using av ailable fabrication techniques does not meet the tight limits for fabricating the polymer transducer. Th e MDM overcomes this limitation by using a microfluidic dispersion head that can deposit 3 to 10 picoliters of the electrode layer dissolved in a solvent at a high throughput. The MDM in its existing configuration can be used to fabricate micron scale polymer transducers with f eatures 2 microns and above with high accuracy and repeatability. A commercially available piezoelectric deposition head from an inkjet printer is modified and used to disperse the electrode material of controlled thic kness as a concept demonstration. The physical properties of the dispersed fluid are adjusted to meet the requirements of the deposition head to fabricate the prototype. The dispersion fluid used had a viscosity of 3.47 ±0.06 cP, a surface tension of 23.6 ±.1 mNm

Bimolecules have demonstrated the potential to function as active components in energy harvesting devices, biosensors and bioinspired actuators. The bilayer lipid membrane (BLM) formed from lipid molecules and supported in the pores of porous substrates is the standard platform for fabricating the biomolecule based devices. The techniques for forming BLM in an in-vitro environment like lipid painting, Lagmuir-Blodgett, Langmuir-Schaffer and lipid folding methods were developed by researchers in the biophysical community to investigate the properties of membrane bound proteins. While all of these methods can form a BLM and has been used in laboratory research for few decades, they are not equally well-suited for fabricating an engineering device. Of the different methods, the lipid deposition technique for BLM self-assembly and protein insertion is the closest in its qualities to an engineering prototyping method. This article presents a detailed electrical model of the substrates and the BLM formed in the pores from SOPC, POPS:POPE and DPhPC lipids using lipid deposition technique. The equivalent circuits of the substrates and the BLM are used to interrogate the quality of the BLM by impedance spectroscopy. The deviations of the prepared BLMs from desirable parameters are traced to the preparation procedure that could be used as a feedback information for fabricating a single BLM in the pores of the substrate. The impedance response is also used to understand the change in electrical properties of BLMs formed in an array of pores of a multi-porous substrate.

Plants have the ability to develop large mechanical force from chemical energy available with bio-fuels. The energy released by the cleavage of a terminal phosphate ion during the hydrolysis of a bio-fuel assists the transport of ions and fluids in cellular homeostasis. Materials that develop pressure and hence strain similar to the response of plants to an external stimuli are classified as nastic materials. This new class of actuators use protein transporters as functional units to move species and result in deformation [Leo et al 2005 (Proceedings of IMECE - 06)]. The ion transporters are hydrocarbons which are formed across the cellular membranes. The membranes that house the ion transporters are aggregates of phospholipids rigidized by cytoskeleton. Reconstituting these nano-machines on a harder matrix is quintessential to build a functional device. Artificial phospholipid membranes or Biliayer lipid membranes (BLM) have poor structural integrity and do not adhere to most surfaces. Patterned arrays of pores made on Poly-propylene glycol-diacrylate (PPG-DA) substrate, a photo curable polymer was made available to us for initial design iterations for an actuator. Hydrophobicity of PPG-DA posed initial problems to support a BLM. We modified the surface of micropatterned PPG-DA membrane by gold plating it. The surface of the porous PPG-DA membranes was plated with gold (Au). A 10nm seeding layer of Au was sputtered on the surface of the membrane. Further gold was reduced onto the sputtered gold surface [Supriya et al(Langmuir 2004, 20, 8870-8876)] by suspending the samples in a solution of hydroxylamine and Hydrogen tetrachloroaurate(III) trihydrate [HAuCl4.3H2O]. This reduction process increased the thickness of the gold, enhanced its adhesion to the PPG-DA substrate and improved the shapes of the pores. This surface modification of PPG-DA helped us form stable BLM with 1-Palmitoyl-2-Oleoyl-sn-Glycero-3- [Phospho-L-Serine] (Sodium Salt) (POPS), 1-Palmitoyl-2-Oleoyl-sn-Glycero- 3-Phosphoethanolamine (POPE) lipids. The observed ionic resistance of the BLM remained stable and sustained 4 mm water column for the the four hours observation period. This article describes the procedure we adopted to modify the PPG-DA substrate, form a BLM and the procedure to quantify the stability of the BLM formed with -amine and -thiol head groups in the lipids.

Conducting polymers are electroactive materials that undergo conformal relaxation of the polymer backbone in the presence of an electrical field through ion exchange with solid or aqueous electrolytes. This conformal relaxation and the associated morphological changes make conducting polymers highly suitable for actuation and sensing applications. Among smart materials, bioderived active materials also use ion transport for sensing and actuation functions via selective ion transport. The transporter proteins extracted from biological cell membranes and reconstituted into a bilayer lipid membrane in bioderived active materials regulate ion transport for engineering functions. The protein transporter reconstituted in the bilayer lipid membrane is referred to as the bioderived membrane and serves as the active component in bioderived active materials. Inspired by the similarities in the physics of transduction in conducting polymers and bioderived active materials, an integrated ionic device is formed from the bioderived membrane and the conducting polymer membrane. This ionic device is fabricated into a laminated thin-film membrane and a common ion that can be processed by the bioderived and the conducting polymer membranes couple the ionic function of these two membranes. An integrated ionic device, fabricated from polypyrrole (PPy) doped with sodium dodecylbenzenesulfonate (NaDBS) and an alamethicin-reconstituted DPhPC bilayer lipid membrane, is presented in this paper. A voltage-gated sodium current regulates the electrochemical response in the PPy(DBS) layer. The integrated device is fabricated on silicon-based substrates through microfabrication, electropolymerization, and vesicle fusion, and ionic activity is characterized through electrochemical measurements.

Ionic electroactive polymers and bioderived materials have been independently demonstrated as actuators, sensors and energy harvesting devices. In an electroactive polymer, the applied electric field between the cathode and anode drives ion transport between the electrodes, impregnated electrolyte and the bulk of the polymer to generate force and displacement. Similarly, in a bioderived material an input stimulus (electrical, chemoelectrical or chemical) applied across the protein in a bilayer lipid membrane (BLM) displaces ions across the membrane barrier and enables sensing and actuation functions. This paper presents a novel architecture for a device that integrates the ionic function of an electroactive polymer and a bioderived material into a thin-film laminated device combining their unique advantages. A conducting polymer (PPy(DBS)) is used as the electroactive polymer and alamethicin-bound bilayer lipid membrane is used as the bioderived material in the thin-film laminated device. Owing to the configuration of the laminated device, the protein regulates the ionic concentration in the conducting polymer and regulates the electrochemical doping/undoping process in the polymer. By electrically connecting the conducting polymer across its thickness, this arrangement provides a mechanism external to the polymer besides electrical field that can control the electrical, mechanical and/or optical properties of the conducting polymer. This paper also presents the fabrication and characterization of the integrated ionic device and presents a template for the development of a novel category of electroactive ionic devices.