Polypyrrole Derivatives: Preparation, Properties and Application

Polypyrrole (PPy) has attracted widespread attention due to its excellent environmental stability, high conductivity, simple synthesis, good biocompatibility, and reversible redox properties. PPy derivatives not only inherit the advantages of polypyrrole, but also have some unique properties. The side and N-site substitution of PPy can not only yield polymers with good solubility, but it also endows polymers with special functionalities by controlling the introduced functional groups. The performance of copolymers can also be adjusted by the type of monomer or polymerization ratio. In this review, an overview of the different types, main preparation methods, and the application prospects of PPy derivatives reported to date are summarized and presented. The current challenges and future opportunities in this research area are also prospected.

Nanoarchitectonics of Nanocellulose Filament Electrodes by Femtosecond Pulse Laser Deposition of ZnO and In Situ Conjugation of Conductive Polymers

Electroactive filament electrodes were synthesized by wet-spinning of cellulose nanofibrils (CNF) followed by femtosecond pulse laser deposition of ZnO (CNF@ZnO). A layer of conducting conjugated polymers was further adsorbed by in situ polymerization of either pyrrole or aniline, yielding systems optimized for electron conduction. The resultant hybrid filaments were thoroughly characterized by imaging, spectroscopy, electrochemical impedance, and small- and wide-angle X-ray scattering. For the filaments using polyaniline, the measured conductivity was a result of the synergy between the inorganic and organic layers, while the contribution was additive in the case of the systems containing polypyrrole. This observation is rationalized by the occurrence of charge transfer between ZnO and polyaniline but not that with polypyrrole. The introduced conductive hybrid filaments displayed a performance that competes with that of metallic counterparts, offering great promise for next-generation filament electrodes based on renewable nanocellulose.

Recent Developments and Implementations of Conductive Polymer-Based Flexible Devices in Sensing Applications

Flexible sensing devices have attracted significant attention for various applications, such as medical devices, environmental monitoring, and healthcare. Numerous materials have been used to fabricate flexible sensing devices and improve their sensing performance in terms of their electrical and mechanical properties. Among the studied materials, conductive polymers are promising candidates for next-generation flexible, stretchable, and wearable electronic devices because of their outstanding characteristics, such as flexibility, light weight, and non-toxicity. Understanding the interesting properties of conductive polymers and the solution-based deposition processes and patterning technologies used for conductive polymer device fabrication is necessary to develop appropriate and highly effective flexible sensors. The present review provides scientific evidence for promising strategies for fabricating conductive polymer-based flexible sensors. Specifically, the outstanding nature of the structures, conductivity, and synthesis methods of some of the main conductive polymers are discussed. Furthermore, conventional and innovative technologies for preparing conductive polymer thin films in flexible sensors are identified and evaluated, as are the potential applications of these sensors in environmental and human health monitoring.

Conductive and Tough Hydrogels Based on Biopolymer Molecular Templates for Controlling in Situ Formation of Polypyrrole Nanorods

Conductive hydrogels (CHs) have gained significant attention for their wide applications in biomedical engineering owing to their structural similarity to soft tissues. However, designing CHs that combine biocompatibility with good mechanical and electrical properties is still challenging. Herein, we report a new strategy for the fabrication of tough CHs with excellent conductivity, superior mechanical properties, and good biocompatibility by using chitosan framework as molecular templates for controlling conducting polypyrrole (PPy) nanorods in situ formation inside the hydrogel networks. First, polyacrylamide/chitosan (CS) interpenetrating polymer network hydrogel was synthesized by UV photopolymerization; second, hydrophobic and conductive pyrrole monomers were absorbed and fixed on CS molecular templates and then polymerized with FeCl₃ in situ inner hydrophilic hydrogel network. This strategy ensured that the hydrophobic PPy nanorods were uniformly distributed and integrated with the hydrophilic polymer phase to form highly interconnected conductive path in the hydrogel, endowing the hydrogel with high conductivity (0.3 S/m). The CHs exhibited remarkable mechanical properties after the chelation of CS by Fe³⁺ and the formation of composites with the PPy nanorods (fracture energy 12 000 J m^-2 and compression modulus 136.3 MPa). The use of a biopolymer molecular template to induce the formation of PPy nanostructures is an efficient strategy to achieve conductive multifunctional hydrogels.

Cellulose-Based Hydrogels with Controllable Electrical and Mechanical Properties

Electrically conductive cellulose-based hydrogels are prepared by a facile and environmentally friendly method, of which the electrical and mechanical properties can be easily controlled by varying the graphene loading. With an ultralow initial addition of graphene oxide (GO, 0.2 wt% versus the mass of cellulose), the resulting cellulose/reduced graphene oxide (CG0.2) hydrogel shows a significantly enhanced compressive modulus of 332.01 kPa, 54.8% higher than that of pure cellulose hydrogel. Further increasing the addition of GO to 2 wt% (versus the mass of cellulose), the electrical conductivity of the resultant CG2.0 hydrogel is as high as 7.3×10−3 S/m, 10,000-fold higher than that of pure cellulose hydrogel, and of which the mechanical properties are also enhanced. These cellulose-based hydrogels with controllable electrical and mechanical properties have a great potential for application in drug delivery and artificial muscle.