Hybrid PVDF/PVDF-graft-PEGMA Membranes for Improved Interface Strength and Lifetime of PEDOT:PSS/PVDF/Ionic Liquid Actuators

Conducting polymer hydrogels for biomedical application: Current status and outstanding challenges

Conducting polymer hydrogels (CPHs) are composite polymeric materials with unique properties that combine the electrical capabilities of conducting polymers (CPs) with the excellent mechanical properties and biocompatibility of traditional hydrogels. This review aims to highlight how the unique properties CPHs have from combining their two constituent materials are utilized within the biomedical field. First, the synthesis approaches and applications of non-CPH conductive hydrogels are discussed briefly, contrasting CPH-based systems. The synthesis routes of hydrogels, CPs, and CPHs are then discussed. This review also provides a comprehensive overview of the recent advancements and applications of CPHs in the biomedical field, encompassing their applications as biosensors, drug delivery scaffolds (DDSs), and tissue engineering platforms. Regarding their applications within tissue engineering, a comprehensive discussion of the usage of CPHs for skeletal muscle prosthetics and regeneration, cardiac regeneration, epithelial regeneration and wound healing, bone and cartilage regeneration, and neural prosthetics and regeneration is provided. Finally, critical challenges and future perspectives are also addressed, emphasizing the need for continued research; however, this fascinating class of materials holds promise within the vastly evolving field of biomedicine.

Ultrasensitive mechanical/thermal response of a P(VDF-TrFE) sensor with a tailored network interconnection interface

Ferroelectric polymers have great potential applications in mechanical/thermal sensing, but their sensitivity and detection limit are still not outstanding. We propose interface engineering to improve the charge collection in a ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) copolymer (P(VDF-TrFE)) thin film via cross-linking with poly(3,4-ethylenedioxythiophene) doped with polystyrenesulfonate (PEDOT:PSS) layer. The as-fabricated P(VDF-TrFE)/PEDOT:PSS composite film exhibits an ultrasensitive and linear mechanical/thermal response, showing sensitivities of 2.2 V kPa^-1 in the pressure range of 0.025-100 kPa and 6.4 V K^-1 in the temperature change range of 0.05-10 K. A corresponding piezoelectric coefficient of -86 pC N^-1 and a pyroelectric coefficient of 95 μC m^-2 K^-1 are achieved because more charge is collected by the network interconnection interface between PEDOT:PSS and P(VDF-TrFE), related to the increase in the dielectric properties. Our work shines a light on a device-level technique route for boosting the sensitivity of ferroelectric polymer sensors through electrode interface engineering.

Electroactive Soft Actuators Based on Columnar Ionic Liquid Crystal/Polymer Composite Membrane Electrolytes Forming 3D Continuous Ionic Channels

Here, we report low-voltage-driven fast-response nanostructured columnar ionic liquid crystal/polymer composite actuators that form three-dimensional continuous ion channels. A three-component self-assembly of a zwitterionic rod-like molecule (49.5 wt %), an ionic liquid (27.5 wt %), and poly(vinyl alcohol) (23.0 wt %) provided a free-standing stretchable membrane electrolyte. The dissociated ions can move through a continuous 3D ionophilic matrix surrounding the hydrophobic columns formed by the hexagonally organized rod-mesogens. Three-layer actuators composed of the electrolyte film sandwiched between two conductive polymer film electrodes of doped polythiophene exhibited a bending motion with 0.32% strain and moved 2 mm within 220 ms under 1 V at 0.1 Hz in 70% relative humidity due to the formation of electric double layers at the soft solid electrolyte/electrode interfaces. The bending strain of the columnar nanostructured actuator is comparable to those of polymer iongel actuators and block polymer actuators containing 25-80 wt % of ionic liquids. It is noteworthy that a small number of ions organized into the 3D nanochannels can generate the large bending deformation, which can contribute to reduce the risk of leakage of ions and the production cost. In addition, we have demonstrated a low-voltage-driven deformable mirror actuator that is expected to be applied to optical devices.

Amidoxime functionalized PVDF-based chelating membranes enable synchronous elimination of heavy metals and organic contaminants from wastewater

Aiming at the synchronous elimination of heavy metals and organic contaminants from wastewater, the amidoxime functionalized PVDF-based chelating membrane was fabricated in this study. The structure and morphology of the chelating membrane were characterized using infrared spectroscopy (FT-IR), nuclear magnetic resonance spectrometer (NMR) and scanning electron microscopy (SEM). The SEM results show that the chemical modification with amidoxime groups did not damage the structure of the PVDF-based membrane. The chelating membrane has a high removal efficiency for Cu²⁺ (77.33%) and Pb²⁺ (79.23%) owing to the chemisorption through coordination bonds. However, the chelating membrane exhibits a low removal efficiency for Cd²⁺ (29.88%) due to the physical adsorption. The chelating membrane has a high rejection efficiency of BSA (95.17%) and lysozyme (70.09%), which is attributed to the sieving effect and increased hydrophobicity. Furthermore, the membrane performance for simultaneously removing metals and proteins from simulated wastewater was examined. The interaction of metal ions with proteins (BSA and lysozyme) can enhance the ion removal efficiency of the chelated membrane, but decrease the protein rejection efficiency due to the destructive effect. The amidoxime functionalized PVDF-based chelating membrane has a high potential for application in wastewater treatment.

Composites, Fabrication and Application of Polyvinylidene Fluoride for Flexible Electromechanical Devices: A Review

The technological development of piezoelectric materials is crucial for developing wearable and flexible electromechanical devices. There are many inorganic materials with piezoelectric effects, such as piezoelectric ceramics, aluminum nitride and zinc oxide. They all have very high piezoelectric coefficients and large piezoelectric response ranges. The characteristics of high hardness and low tenacity make inorganic piezoelectric materials unsuitable for flexible devices that require frequent bending. Polyvinylidene fluoride (PVDF) and its derivatives are the most popular materials used in flexible electromechanical devices in recent years and have high flexibility, high sensitivity, high ductility and a certain piezoelectric coefficient. Owing to increasing the piezoelectric coefficient of PVDF, researchers are committed to optimizing PVDF materials and enhancing their polarity by a series of means to further improve their mechanical-electrical conversion efficiency. This paper reviews the latest PVDF-related optimization-based materials, related processing and polarization methods and the applications of these materials in, e.g., wearable functional devices, chemical sensors, biosensors and flexible actuator devices for flexible micro-electromechanical devices. We also discuss the challenges of wearable devices based on flexible piezoelectric polymer, considering where further practical applications could be.

Self-Standing High-Performance Transparent Actuator Based on Poly(dimethylsiloxane)/TEMPO-Oxidized Cellulose Nanofibers/Ionic Liquid Gel

The sustainable application of cellulose nanofibers and ionic liquids (ILs) in the fabrication of transparent gel electrolyte actuators combined with thin electrodes remains to be explored. Accordingly, this study developed a new actuator on the basis of a 2,2,6,6-tetramethylpiperidine-1-oxyl radical-oxidized cellulose nanofibers/IL/poly(dimethylsiloxane) (TOCN/IL/PDMS) transparent gel electrolyte. A casting method was employed to prepare the gel electrolyte film, and spray-coating was used to apply thin electrodes. On the basis of its electromechanical and electrochemical properties, the TOCN/IL/PDMS gel electrolyte actuator had high strain performance. The actuator's operational mechanism is based on both electrostatic double-layer capacitor (EDLC) and Faradaic capacitor mechanisms, with the EDLC mechanism having a stronger influence. The actuator's displacement-response frequency dependency was determined, and we simulated the obtained findings by using a double-layer charging kinetic model. The combined gel electrolyte and electrode resistance resulted in a favorable fit to the experimental data, as did the gel electrolyte resistance alone. The performance of the TOCN/IL/PDMS-electrolyte-based polymer actuators can be improved further by designing electrolytes (primarily) and electrodes to have high ionic and electrical conductivities. The films-which are flexible, robust, and transparent-may have potential as actuator materials within electronic and energy-conversion devices that are required to be wearable and transparent.

Conjugated Polymer Actuators and Devices: Progress and Opportunities

Conjugated polymers (CPs), as exemplified by polypyrrole, are intrinsically conducting polymers with potential for development as soft actuators or "artificial muscles" for numerous applications. Significant progress has been made in the understanding of these materials and the actuation mechanisms, aided by the development of physical and electrochemical models. Current research is focused on developing applications utilizing the advantages that CP actuators have (e.g., low driving potential and easy to miniaturize) over other actuating materials and on developing ways of overcoming their inherent limitations. CP actuators are available as films, filaments/yarns, and textiles, operating in liquids as well as in air, ready for use by engineers. Here, the milestones made in understanding these unique materials and their development as actuators are highlighted. The primary focus is on the recent progress, developments, applications, and future opportunities for improvement and exploitation of these materials, which possess a wealth of multifunctional properties.

Heteroatoms doped metal iron-polyvinylidene fluoride (PVDF) membrane for enhancing oxidation of organic contaminants

Iron nanoparticles (NPs) embedded in S, N-codoped carbon were prepared by one-step pyrolysis of a homogeneous mixture consisting of Fe, S, N, C precursors, and then immobilized in poly (vinylidene fluoride) membranes as a multifunctional catalytic system (NSC-Fe@PVDF) to effectively activate peroxymonosulfate (PMS) and oxidize organic compounds in water. The NSC-Fe@PVDF membranes effectively decolorized organic pollutants at a wide pH range (2.05-10.85), due to the synergistic effects between the S, N-doped carbon and iron NPs. The efficiency depended on the doping types, amount of metal, PMS dosages, reaction temperatures, solution pHs, and organic substrates. In-situ electron spin resonance spectroscopy and sacrificial-reagent incorporated catalysis indicate radical intermediates such as sulfate and hydroxyl radicals are mainly responsible for this persulfate-driven oxidation of organic compounds. Membrane's porous structure and high internal surface area not only minimize the NPs agglomeration, but also allow the facile transport of catalytic reactants to the active surface of metal catalysts. The results demonstrate the morphological and structural features of catalytic membranes enhance the overall catalytic activity.

Plasma-Based Nanostructuring of Polymers: A Review

There are various fabrication methods for synthesizing nanostructures, among which plasma-based technology is strongly competitive in terms of its flexibility and friendly uses, economy, and safety. This review systematically discusses plasma techniques and the detailed interactions of charged particles, radicals, and electrons with substrate materials of, in particular, polymers for their nanostructuring. Applications employing a plasma-based nanostructuring process are explored to show the advantages and benefits that plasma treatment brings to many topical and traditional issues, and are specifically related to wettability, healthcare, or energy researches. A short perspective is also presented on strategic plans for overcoming the limitations in dimension from surface to bulk, lifetime of surface functions, and selectivity for interactions.

Spray-coated carbon nanotube carpets for creeping reduction of conducting polymer based artificial muscles

During cyclic actuation, conducting polymer based artificial muscles are often creeping from the initial movement range. One of the likely reasons of such behaviour is unbalanced charging during conducting polymer oxidation and reduction. To improve the actuation reversibility and subsequently the long time performance of ionic actuators, we suggest using spray-coated carbon nanotube (CNT) carpets on the surface of the conducting polymer electrodes. We show that carbon nanotubes facilitate a conducting polymer redox reaction and improve its reversibility. Consequently, in the long term, charge accumulation in the polymer film is avoided leading to a significantly improved lifetime performance during cycling actuation. To our knowledge, it is the first time a simple solution to an actuator creeping problem has been suggested.

High-Performance PEDOT:PSS/Single-Walled Carbon Nanotube/Ionic Liquid Actuators Combining Electrostatic Double-Layer and Faradaic Capacitors

New hybrid-type poly(3,4-ethylenedioxythiophene) (PEDOT) actuators produced by the film-casting method, in which both electrostatic double-layer (EDLC) and faradaic capacitors (FCs) occur simultaneously, have been developed. The electrochemical and electromechanical properties of

PEDOT

poly(4-styrenesulfonate) (PSS), PEDOT:PSS/ionic liquid (IL), and

PEDOT

PSS/single-walled carbon nanotubes (SWCNTs)/IL actuators are compared with those of a conventional poly(vinylidene fluoride)-co-hexafluoropropylene (PVdF(HFP))/SWCNT/IL actuator. It is found that the

PEDOT

PSS/SWCNT/IL actuator provides a better actuation strain performance than a conventional (PVdF(HFP))/SWCNT/IL actuator, as its electrode is an electrochemical capacitor (EC) composed of an EDLC and FC. The

PEDOT

PSS polymer helps produce a high specific capacitance, actuation strain, and maximum generated stress that surpass the performance of a conventional PVdF(HFP) actuator. The flexible and robust films created by the synergistic combination of PEDOT and SWCNT may therefore have significant potential as actuator materials for wearable energy-conversion devices. A double-layer charging kinetic model was successfully used to simulate the frequency dependence of the displacement responses of the

PEDOT

PSS/IL and

PEDOT

PSS/SWCNT/IL actuators.

Light-Activated Rapid-Response Polyvinylidene-Fluoride-Based Flexible Films

The design strategy and mechanical response mechanism of light-activated, rapid-response, flexible films are presented. Practical applications as a microrobot and a smart spring are demonstrated.