Variable Emittance Electrochemical Devices for Spacecraft Application based on Ionic Liquids Coupled with Conducting Polymers

P-Type Chemical Doping-Induced High Bipolar Electrical Conductivities in a Thermoelectric Donor–Acceptor Copolymer

Biopotentials, which encompass action potentials and plant-specific biopotentials, play a crucial role in cell-to-cell communication and propagate within ionically conductive bio-tissues. Monitoring electrophysiology signals using electronic devices offers a real-time diagnostic approach for various diseases. The emergence of conducting polymer (CP)-based flexible bioelectronics has revolutionized high-quality signal acquisition by seamlessly interfacing with bio-tissues. In this thesis, we explore CP-based bioelectronics in the form of microneedle (MN) patch and hygroscopic adhesive, and investigate their performance in electrophysiology monitoring. Firstly, we introduce the concept of a CP-based dual-conductive stiff-morphing MN patch (DuoMorph) designed for in planta electrophysiology monitoring. By integrating CP PEDOT:PSS with thermoplastic poly lactic-co-glycolic acid (PLGA), we create a thermos-pressed DuoMorph capable of penetrating poorly conductive epidermal barriers in a minimally invasive manner. The stiffness-morphability of the DuoMorph ensures a low mechanical mismatch with soft plant tissues, effectively suppressing potential foreign body responses. Additionally, the addition of dimethyl sulfoxide (DMSO) further enhances the conductivity of CP. In vitro electrochemical impedance spectroscopy conducted on agarose-based epidermal phantoms and Epipremnum aureum leaves reveals significantly lower bio-electronic interface impedance compared to invasive metallic electrodes. This improvement is attributed to the low charge transfer resistance (Rct) and high double-layer capacitance (Cdl) of PEDOT:PSS. Demonstrations on living Epipremnum aureum plants successfully capture variation potentials induced by mechanical wounding and flame burning. Furthermore, the “lock” effect induced by sap adsorption ensures a better signal-tonoise ratio (SNR) and improved anti-interference capability compared to metallic electrodes. Finally, the DUOMORPH coated with a cation-selective membrane enables real-time in situ ion fluctuation capture, highlighting its potential as a versatile sensing platform for multiple bio-signals. Secondly, inspired by spider silk, we developed an electronically conductive hygroscopic adhesive (HydroAd) that enables a chronic bio-electronic interface. Unlike conventional wet electrodes, which fail due to electrolyte volatilization, and dry electrodes, which provide poor signal quality due to high interface impedance, HydroAd offers significant advantages. HydroAd contains an electrolyte that moistens the stratum corneum, reducing interface impedance to levels lower than those of commercial wet electrodes (CWE). It also maintains a water balance between evaporation and adsorption over long-term period. The incorporation of a crosslinkable charged ionic liquid into CP enhances its electrical properties. Specifically, this modification improves conductivity and increases charge storage and injection capacity by facilitating CP conductive network. The crosslinkable ionic liquid also acts as plasticizer that improves CP’s stretchability. Additionally, the ionic liquid’s hygroscopic nature allows it to function as a superabsorbent, leading to strong electrostatic interactions with water molecules. Gelatin methacryloyl (GelMA) enhances HydroAd's adhesiveness, and by adjusting the composition of the initiator and crosslinker, its adhesiveness can be optimized. Notably, HydroAd maintains a resistance variation of approximately 2.5% and an impedance variation below 10% during cyclic stretching tests. It achieves stable electrical properties and adhesiveness over a record-breaking six-month period. Applications in biopotential monitoring, such as electrocardiogram (ECG), electroencephalogram (EEG), and electrooculogram (EOG), demonstrate that HydroAd offers better signal acquisition quality, with no SNR change observed after a six-month drying process. This highlights its potential as a chronic bio-electronic platform. Finally, we explored the mechanism behind the remarkable water permeability of the HydroAd. Compared to conventional hygroscopic compounds used in electronically conductive adhesives (such as LiCl and uncrosslinked choline-based ionic liquids), HydroAd exhibits even higher water permeability. It surpasses not only conventional encapsulation materials like PDMS (Polydimethylsiloxane), PI (Polyimide), and highly permeable thermoplastic polyurethane (TPU) but also the CWE. Raman spectroscopy and differential scanning calorimetry confirmed that after crosslinking, the charged network within HydroAd modulates the water state, increasing the ratio of intermediate water (loosely bound) to bound water (strongly bound), denoted as the I/B ratio. This adjustment decreases the overall water enthalpy, resulting in improved electrode breathability. On sweaty skin, HydroAd’s high permeability enables rapid water evaporation and adhesion recovery within just 30 minutes. Further investigation revealed that the high I/B ratio plays a crucial role in regulating both electrochemical and mechanical properties. Specifically, it leads to decreased electrical impedance and enhanced adhesion. By triggering the formation of electrochemical interface, the higher content of intermediate water enhances the Cdl while suppressing electrolyte resistance (Rs) and Rct. To demonstrate its practical application, we designed a 10-channel HydroAd electrode array for surface electromyography (sEMG)-based gesture recognition. Remarkably, HydroAd-based gesture recognition achieves an impressive prediction accuracy of over 95%, surpassing both metallic dry electrodes and CWE. Even after a six-month drying process, its performance remains unchanged. This positions HydroAd as an ideal platform for advanced human-machine interaction.

Sputtered transparent electrodes for optoelectronic devices: Induced damage and mitigation strategies

This paper presents an experimental study of augmentation of pool boiling heat transfer characteristics of different nanoscale-coated thin film (TF) surfaces using water as boiling liquid at atmospheric pressure. The heating surfaces used for experiments are untreated, treated using emery grits no. 2000 and treated with TiO2 nanoscale coated having thicknesses of 100, 200 and 300 nm thin film surfaces. The thin films were grown on copper substrate by physical vapor deposition method. The surfaces were characterized with respect to contact angle (sessile droplet method), film thickness (thickness monitor) and surface roughness (surface profilometer). The experiments were conducted in a closed boiling vessel at atmospheric pressure. Heat flux was varied from 52.63 to 144.73 W/cm2. The analysis of experimental data revealed that there is a reduction of about 40.3 % in the incipience superheat for the applied heat for thickest nanoscale coating surface over a untreated surface. It was observed that thin film surface is superior than the treated and untreated surfaces in view of boiling heat transfer coefficient. The maximum of 80.3, 60.2, 29.6, and 11.5 % enhancement in heat transfer coefficient were observed for TiO2 nanoscale-coated TF having thicknesses of 300, 200 and 100 nm and treated surfaces, respectively, compared to untreated surfaces. The highest enhancement of heat transfer coefficient in nanoscale-coated thin film surfaces was due to better liquid spreading, enhanced wettability and active nucleate site density. The maximum uncertainty in heat transfer coefficient was found in the range of ±2.69 %.

To measure the distribution of local contractile movements in the layer of the myotubes, the movement of the matrix pattern of micro-markers placed on the back surface of the thin film to which the myotubes were attached has been tracked in vitro. A matrix pattern of micro-markers (diameter 4 μm, height 2 μm, spacing 30 μm) was created on the back surface of a polydimethylsiloxane thin film (thickness 6 μm) using photolithography technology. Mouse myoblasts were seeded on the front surface of the thin film and incubated for 10 days to differentiate into myotubes. Periodic electrical pulses (amplitude 2 V, pulse period 0.5 s, pulse width 1 ms) were applied between the electrodes of the titanium wire immersed in the medium. The movements of both the myotubes and the markers were observed simultaneously with an optical microscope. Experimental results show that the distribution of movement for each marker is related to the local periodic movement of the myotubes layer. A thin film with matrix pattern micro-markers created on the back side may allow in vitro analysis of the distribution of local repetitive contractile movements in the myotubes layer.

Technological demands for the fabrication of nanostructured active coatings provide renewed motivation for understanding the properties that control the morphology of the thin film surface. With decreasing structure size, the issues of finite size and shape effects become non-negligible including issues of stability against decay and structural rearrangement. The surface of the wide band gap semiconductor ZnO is known to be very active, with a wide variety of absorption and chemisorptions phenomena taking place. These processes can alter the charge carrier distribution in the sub-surface region and locally change the doping levels. There is a limited amount of literature dedicated to systematic and detailed studies on the surface evolution with growth parameters and their effect on the ZnO surface conductivity under reduction/oxidation. Therefore, this work focuses on the analysis of the thin ZnO film surface properties by studying specific surface parameters such as amplitude related parameters (average roughness, the root mean square), mixed parameters (surface area ratio), functional parameters for characterizing bearing and fluid retention (skewness), and spatial parameters (the fractal dimensions) as they correlate with the film conductivity changes under subsequent exposure to UV light (as reductor factor) and ozone (as surface oxidant agent). All ZnO thin films of different thicknesses were grown by the dc planar magnetron sputtering technique under the same sputtering conditions.

Polyvinyl alcohol‐based polymeric films with NaI and ionic liquid (1‐Butyl‐1‐methylpyrrolidinium hexafluorophosphate) have been developed by using the solution cast method. The produced polymer electrolyte sheets were evaluated using various methods. Electrochemical impedance spectroscopy was utilized to measure the conductivity of the polymeric films, and the ionic liquid doped films showed an increase with a maximum at 6 wt% ionic liquid with a value for conductivity of 4.545 × 10−4 S cm−1. The morphological features of the most conductive polymer were further investigated using polarized optical microscopy and x‐ray diffraction. Ionic doping causes an increase in the amorphous nature. Using Fourier transform infrared spectroscopy, an excellent complexity between PVA, salt NaI, and ionic liquid was assessed. Thermogravimetric analysis was used to inspect the polymer films' thermal stability. The highest conducting sample was used for manufacturing an electric double‐layer capacitor. The behavior of manufactured electric double‐layer capacitor has been evaluated through EIS, CV, and GCD.

11 - Tactile sensors based on ionic liquids

Si thin films are attracted as materials for ultra-large-scale solar cell systems at relatively low cost. Electrodeposition is expected as one fabrication method of Si thin films due to its advantages such as relatively simplicity process, precision control of nanostructure and continuous deposition in large area. Si thin films have been electrodeposited in non-aqueous solvents owing to their large electrochemical windows which allows for the study of Si electrodeposition [1-3]. Among various non-aqueous solvents, organic solvents and ionic liquids, which can be used under low temperature, have been used as electrolytes for the electrodeposition of Si thin films in our laboratory. We have previously succeeded to electrodeposit Si thin films in organic solvents and ionic liquids [4-6]. However, there is a problem for applications to solar cells that some impurities (mainly carbon and oxygen) are incorporated in thin films. We have reported the carbon content can be reduced by annealing treatment [7]. On the other hand, the decrease of oxygen content is still required. Thus, we evaluate the composition of Si thin films electrodeposited in an organic solvent and an ionic liquid without oxygen atoms in order to analysis the effect of bath conditions on the composition of thin films (especially, where the oxygen incorporated in Si thin films comes from). Si thin films were electrodeposited with 3 electrode cell (W.E. : Au, R.E. : Ag/Ag+, C.E. : Pt) in acetonitrile, 0.3 M tetrabutylammonium chloride and 0.5 M SiCl4 was used as an organic solvent, and 1-butyl-3-methylimidazolium hexafluorophosphate and 0.5 M SiCl4 as an ionic liquid. The composition of Si thin films were evaluated by X-ray photoelectron spectroscopy. As a result, the oxygen content in Si thin films were decreased by using the solvents without oxygen atoms in both organic solvent and ionic liquid cases. This results suggest that the reason the oxygen inclusion is derived from the incorporation of solvents themselves in films during electrodeposition, and propose us the way to obtain films with low impurities. In addition, the rotating disk electrode was used in the organic solvent case in order to promote the convection. The usage of this rotating disk electrode showed the decrease of impurities in Si thin films. Therefore, it is indicated that the stable supply of SiCl4 to the electrode surface is important factor to obtain films with low impurities. This study reveals that bath condition significantly affects to the composition of Si thin films, and could help us to fabricate films for applications to solar cells. This study was financially supported in part by the Japan Science and Technology Agency (JST) CREST program, and Y. T. acknowledges the Leading Graduate Program in Science and Engineering, Waseda University, from MEXT, Japan. [1] S. Zein El Abedin, N. Borrissenko, F. Endres, Electrochem. Comm., 6 (2004) 510. [2] T. Munisamy, A. J. Bard, Electrochim. Acta, 55 (2010) 3797. [3] M. Bechelany, J. Elias, P. Brodard, J. Michler, L. Philippe, Thin Solid Films 520 (2012) 1895. [4] Y. Nishimura and Y. Fukunaka, Electrochim. Acta, 53 (2007) 111. [5] T. Homma, J. Komadina, Y. Nakano, T. Ouchi, T. Akiyoshi, Y. Ishibashi, Y. Nishimura, T. Nishida, and Y. Fukunaka, Electrochem. Soc. Trans., 41 (2012) 9. [6] J. Komadina, T. Akiyoshi, Y. Ishibashi, Y. Fukunaka, T. Homma, Electrochim. Acta, 100 (2013) 236. [7] Y. Tsuyuki, A. Pham, J. Komadina, Y. Fukunaka, T. Homma, Electrochim. Acta, 183 (2015) 49.

Deposition characteristics of CoCrFeMnNi high-entropy alloys thin film via simulation

Conducting polymers, because of their promising potential to replace silicon and metals in building devices, have attracted great attention since the discovery of high conductivity in doped polyacetylene in 1977. Lithographic techniques present significant technical challenges when working with conducting polymers. Sensitivity of conducting polymers to environmental conditions (e.g., air, oxygen, moisture, high temperature, and chemical solutions) makes current photolithographic methods unsuitable for patterning the conducting polymers due to the involvement of wet and/or dry etching processes in those methods. Existing non-photolithographic approaches have limitations in throughput, resolution, or electrical insulation. Therefore, an intermediate-layer lithography (ILL) approach has been recently developed by my group to produce conducting polymer micro/nanostructures. In the ILL method, an intermediate layer of an electrically insulating polymer is coated between the substrate and a layer of the conducting polymer to be printed. Subsequently, the conducting polymer is printed through mold insertion using a hot-embossing process. The current hot-embossing based methods face the obstacles of residual layer and depth of field (i.e., the height variation in the mold structures). In contrast, the ILL approach does not leave a residual layer in the material of interest, making conducting polymer patterns isolated from one another and avoiding the shorting problem in the electrical applications of these patterns. Furthermore, in the ILL, the height variation potentially existing among the mold structures has been transferred to the intermediate layer, ensuring that all patterns in the mold have been properly transferred to the conducting polymer layer. In addition to conducting polymers, the ILL can also be applied to pattern metals as well as other types of polymers. This paper gives a review of this ILL method and reports the results that we have achieved to date, including generation and applications of single and multiple layers of microstructures of conducting polymers and aluminum.

Using irradiation effect to study the disparate anchoring stabilities of polar-organic molecules adsorbed on bulk and thin-film metal surfaces

Ionised cluster beams have been produced and employed for thin film deposition and surface processing for half a century. In the last two decades, kiloelectronvolt cluster ions have also proved to be outstanding for surface characterisation by secondary ion mass spectrometry (SIMS), because their sputter and ion yields are enhanced in a non-linear fashion with respect to monoatomic projectiles, with a resulting step change of sensitivity for analysis and imaging. In particular, large gas cluster ion beams, or GCIB, have now become a reference in organic surface and thin film analysis using SIMS and X-ray photoelectron spectroscopy (XPS). The reason is that they induce soft molecular desorption and offer the opportunity to conduct damageless depth-profiling and 3D molecular imaging of the most sensitive organic electronics and biological samples, with a nanoscale depth resolution. In line with these recent developments, the present review focuses on rather weakly-bound, light-element cluster ions, such as noble or other gas clusters, and water or alcohol nanodroplets (excluding clusters made of metals, inorganic salts or ionic liquids) and their interaction with surfaces (essentially, but not exclusively, organic). The scope of this article encompasses three aspects. The first one is the fundamentals of large cluster impacts with surfaces, using the wealth of information provided by molecular dynamics simulations and experimental observations. The second focus is on recent applications of large cluster ion beams in surface characterisation, including mass spectrometric analysis and 2D localisation of large molecules, molecular depth-profiling and 3D molecular imaging. Finally, the perspective explores cutting edge developments, involving (i) new types of clusters with a chemistry designed to enhance performance for mass spectrometry imaging, (ii) the use of cluster fragment ion backscattering to locally retrieve physical surface properties and (iii) the fabrication of new biosurface and thin film architectures, where large cluster ion beams are used as tools to transfer biomolecules in vacuo from a target reservoir to any collector substrate.

Porous polymers have immense potential in catalysis, energy conversion and storage, separation sciences and life sciences due to their high surface area and high diffusion flux. Developing porous polymers with micro and mesoscale porosity with long-range order is challenging and involves multistep templated approaches. Here we demonstrate a simple surface-oxygen induced electropolymerization route to directly obtain self-assembled porous polymers of polyparaphenylene (PPP) and PPP based copolymers in ionic liquids. By combining experimental and theoretical studies, we show that surface oxygen on Cu changes the orientation and assembly of benzene which then results in a change in electropolymerization mechanism leading to a self-assembled porous structure with porosity between 2 and 5 μm. Furthermore, with controlled experimental parameters, bicontinuous conducting polymers with porosity of >10 μm are obtained. The porous conducting polymers show absorption of light in the visible range which was also used as an efficient electrode for investigation of the photoelectrochemical oxygen evolution reaction.

Low vapor pressure and several other outstanding properties make room-temperature ionic liquids attractive candidates as lubricants for machine elements in space applications. Ensuring sufficient liquid lubricant supply under space conditions is challenging, and consequently, such tribological systems may operate in boundary lubrication conditions. Under such circumstances, effective lubrication requires the formation of adsorbed or chemically reacted boundary films to prevent excessive friction and wear. In this work, we evaluated hydrocarbon-mimicking ionic liquids, designated P-SiSO, as performance ingredients in multiply alkylated cyclopentane (MAC). The tribological properties under vacuum or various atmospheres (air, nitrogen, carbon dioxide) were measured and analyzed. Thermal vacuum outgassing and electric conductivity were meas- ured to evaluate ‘MAC & P-SiSO’ compatibility to the space environment, including the secondary effects of radiation. Heritage space lubricants—MAC and perfluoroalkyl polyethers (PFPE)—were employed as references. The results corroborate the beneficial lubricating performance of incorporating P-SiSO in MAC, under vacuum as well as under various atmospheres, and demonstrates the feasibility for use as a multifunctional additive in hydrocarbon base oils, for use in space exploration applications.