Electropolymerization in a confined nanospace: synthesis of PEDOT nanoparticles in emulsion droplet reactors

Conducting Polymer Nanoparticles with Intrinsic Aqueous Dispersibility for Conductive Hydrogels

Conductive hydrogels are promising materials with mixed ionic-electronic conduction to interface living tissue (ionic signal transmission) with medical devices (electronic signal transmission). The hydrogel form factor also uniquely bridges the wet/soft biological environment with the dry/hard environment of electronics. The synthesis of hydrogels for bioelectronics requires scalable, biocompatible fillers with high electronic conductivity and compatibility with common aqueous hydrogel formulations/resins. Despite significant advances in the processing of carbon nanomaterials, fillers that satisfy all these requirements are lacking. Herein, intrinsically dispersible acid-crystalized PEDOT:PSS nanoparticles (ncrys-PEDOTX ) are reported which are processed through a facile and scalable nonsolvent induced phase separation method from commercial PEDOT:PSS without complex instrumentation. The particles feature conductivities of up to 410 S cm-1 , and when compared to other common conductive fillers, display remarkable dispersibility, enabling homogeneous incorporation at relatively high loadings within diverse aqueous biomaterial solutions without additives or surfactants. The aqueous dispersibility of the ncrys-PEDOTX particles also allows simple incorporation into resins designed for microstereolithography without sonication or surfactant optimization; complex biomedical structures with fine features (< 150 µm) are printed with up to 10% particle loading . The ncrys-PEDOTX particles overcome the challenges of traditional conductive fillers, providing a scalable, biocompatible, plug-and-play platform for soft organic bioelectronic materials.

The discrete single-entity electrochemistry of Pickering emulsions

Single-entity analysis is an important research topic in electrochemistry. To date, electrode collisions and subsequent electrode-particle interactions have been studied for many types of nano-objects, including metals, polymers, and micelles. Here we extend this nano-object electrochemistry analysis to Pickering emulsions for the first time. The electrochemistry of Pickering emulsions is important because the internal space of a Pickering emulsion can serve as a reactor or template; this leads to myriad possible applications, all the while maintaining mechanical stability far superior to what is exhibited by conventional emulsions. This work showed that Pickering emulsions exhibit similar hydrodynamic behavior to other nano-objects, despite the complex structure involving hard nanoparticle surfactants, and the electron-transport mechanism into the internal volume of Pickering emulsions was elucidated. The Pickering emulsion electrochemistry platform developed here can be applied to electrochemical nanomaterial synthesis, surmounting the challenges faced by conventional synthetic strategies involving normal emulsions.

Electrochemistry under confinement

Although the term 'confinement' regularly appears in electrochemical literature, elevated by continuous progression in the research of nanomaterials and nanostructures, up until today the various aspects of confinement considered in electrochemistry are rather scattered individual contributions outside the established disciplines in this field. Thanks to a number of highly original publications and the growing appreciation of confinement as an overarching link between different exciting new research strategies, 'electrochemistry under confinement' is the process of forming a research discipline of its own. To aid the development a coherent terminology and joint basic concepts, as crucial factors for this transformation, this review provides an overview on the different effects on electrochemical processes known to date that can be caused by confinement. It also suggests where boundaries to other effects, such as nano-effects could be drawn. To conceptualize the vast amount of research activities revolving around the main concepts of confinement, we define six types of confinement and select two of them to discuss the state of the art and anticipated future developments in more detail. The first type concerns nanochannel environments and their applications for electrodeposition and for electrochemical sensing. The second type covers the rather newly emerging field of colloidal single entity confinement in electrochemistry. In these contexts, we will for instance address the influence of confinement on the mass transport and electric field distributions and will link the associated changes in local species concentration or in the local driving force to altered reaction kinetics and product selectivity. Highlighting pioneering works and exciting recent developments, this educational review does not only aim at surveying and categorizing the state-of-the-art, but seeks to specifically point out future perspectives in the field of confinement-controlled electrochemistry.

Enabling practical nanoparticle electrodeposition from aqueous nanodroplets

The rapid rise of technology in the modern world has led to an increased demand for energy. Consequently, it is essential to increase the efficiency of current energy-producing systems due to the poor activity of their catalysts. Nanoparticles play a significant role in energy storage and conversion; however, electrodeposition of nanoparticles is difficult to achieve due to surface heterogeneities, nanoparticle diffusion layer overlap, and the inability to electrodeposit multi-metallic nanoparticles with stoichiometric control. These problems can be solved through nanodroplet-mediated electrodeposition, a technique where water nanodroplets are filled with metal salt precursors that form stable nanoparticles when they collide with a negatively-biased electrode. Further, this method has demonstrated control over nanoparticle size and morphology, displaying a wide variety of applications for the generation of materials with excellent catalytic properties. Historically, the cost of nanodroplet-mediated electrodeposition experimentation is prohibitive because practitioners use 0.1 M to 0.5 M tetrabutylammonium perchlorate (TBAP) dissolved in the oil phase (∼10 mL). Such high concentrations of electrolytes have been used to lower ohmic drop and provide ions to maintain charge balance during electrodeposition. Here, we show that supporting electrolyte is not necessary for the oil phase. In fact, one can use a suitable salt (such as lithium perchlorate) in the aqueous phase to achieve nanoparticle electrodeposition. This simple change, grounded in an understanding of ion transfer, drives down the cost per experiment by nearly three orders of magnitude, representing a necessary step forward in enabling practical nanoparticle electrodeposition from water nanodroplets. This approach is a promising procedure for future cost-effective energy conversion systems relying on electrocatalytic nanoparticles.

In Situ Liquid Phase TEM of Nanoparticle Formation and Diffusion in a Phase-Separated Medium

Colloidal nanoparticles are synthesized in a complex reaction mixture that has an inhomogeneous chemical environment induced by local phase separation of the medium. Nanoparticle syntheses based on micelles, emulsions, flow of different fluids, injection of ionic precursors in organic solvents, and mixing the metal organic phase of precursors with an aqueous phase of reducing agents are well established. However, the formation mechanism of nanoparticles in the phase-separated medium is not well understood because of the complexity originating from the presence of phase boundaries as well as nonuniform chemical species, concentrations, and viscosity in different phases. Herein, we investigate the formation mechanism and diffusion of silver nanoparticles in a phase-separated medium by using liquid phase transmission electron microscopy and many-body dissipative particle dynamics simulations. A quantitative analysis of the individual growth trajectories reveals that a large portion of silver nanoparticles nucleate and grow rapidly at the phase boundaries, where metal ion precursors and reducing agents from the two separated phases react to form monomers. The results suggest that the motion of the silver nanoparticles at the interfaces is highly affected by the interaction with polymers and exhibits superdiffusive dynamics because of the polymer relaxation.

The Electroneutrality Condition Allows for Electrodeposition of Gold Nanoparticles from Aqueous Nanodroplets

Nanodroplet-mediated electrodeposition is a reliable method for electrodepositing nanoparticles by confining a small amount of metal-salt precursor in water nanodroplets (radius ~400 nm) suspended in an oil continuous phase. This...

In Situ Probing Liquid/Liquid Interfacial Kinetics through Single Nanodroplet Electrochemistry

In this study, we report the new application of single nanodroplet electrochemistry to in situ monitor the interfacial transfer kinetics of electroactive species across liquid/liquid interface. Interfacial kinetic information is crucial in drug delivery and membrane transport. However, interfacial information has been mainly studied thermodynamically, such as partition coefficient, which could not manifest a speed of transfer. Herein, we measure the phase-transfer kinetic constant via the steady-state electrochemistry of an extracted redox species in a single nanodroplet. The redox species were transferred from the continuous oil phase to the water nanodroplet by partition equilibrium. The transferred redox species are selectively electrolyzed within the droplet when the droplet contacts with an ultramicroelectrode, while the electrochemical reaction of the redox species outside the droplet (i.e., organic solvent) is effectively suppressed by adjusting the electrolyte composition. The redox species in the water droplets can quickly attain a steady state during electrolysis owing to an extensive mass transfer by radial diffusion, and the steady-state current can be analyzed to obtain kinetic information with help from the finite-element method. Finally, a quick calculation method is suggested to estimate the kinetic constant of phase transfer without simulation.