Scientific publications

Roughening of metal electrodes in batteries is detrimental as it can lead to metal dendrites. Such dendrites can cause short circuits when they grow from the metal electrode to the other one, as can happen during battery operation when metal is plated onto the surface of an electrode. It has been suggested that solid electrolytes of sufficient elastic stiffness can suppress electrode surface roughening and dendriting, although experimental evidence is now emerging that this possibility is not valid. To investigate whether metal electrode surfaces will roughen during battery charging we carry out a linear perturbation analysis. Our calculations explore whether an electrode surface with one-dimensional sinusoidal roughness will experience growth of its amplitude. We assess a linear elastic electrolyte that is a single ion conductor bonded to a metal electrode being plated by a cathodic ionic current. We find that long wavelength perturbations will always increase in roughness. High current densities during battery charging are found to permit growth of the amplitude of small wavelength roughness. The stiffness of the solid electrolyte is found to play a role in limiting the growth of roughness, but its effect can always be overcome at high current densities and for long wavelength protrusions.

An elementary 1-dimensional model is developed for a solid state lithium-ion battery having a single ion conductor electrolyte, a lithium metal negative electrode and a composite positive electrode. The battery topology is assumed to be of the layered variety, thereby justifying the 1-dimensional formulation. The governing equations for the electrochemical kinetics at the interface between the negative electrode and the electrolyte separator are stated, as are those for ion transport in the electrolyte. The positive electrode is assumed to be a particulate composite of storage material within a matrix of electrolyte. A mixture theory is developed for the positive electrode encompassing ion transport in the electrolyte matrix and storage and unstorage of lithium in the active material subject to electrochemical kinetics at the perimeter of the storage particles. Many simplifying assumptions are made with the advantage of them leading to closed-form or semi-closed-form solutions, including linearization of the equations governing the redox kinetics at interfaces in the battery between electrolyte and active material. An approximation is given for the concentration of lithium in the positive electrode of the battery during discharge, with the details depending on a length scale parameter that depends on the competition between the rate of lithium insertion into/extraction from the storage particles and the rate at which lithium ions are transported in the electrolyte. When the conductivity of the electrolyte is high and the redox reactions are relatively sluggish, this length scale parameter is comparable to the thickness of the positive electrode or larger than it. In that case lithium insertion into/extraction from storage particles occurs everywhere within an active zone of the positive electrode, but with the rates least at the current collector of the positive electrode. If the conductivity of the electrolyte is poor and the redox reactions rapid, the length scale for the solution is small compared to the thickness of the positive electrode and insertion into/extraction from storage particles occurs only in a narrow slice of the positive electrode. This slice moved along the positive electrode and separates a region of it that is completely filled/empty from a region of it that has not yet gained or lost any of its lithium. In all cases there will usually be a region of the positive electrode near the separator that is completely filled during discharge and completely empty during battery charging. Our results also give outcomes from which the internal resistance of the battery can be estimated.

Gallium hydride stabilized by the base quinonuclidine reacts with acetone under addition of the Ga-H function to the carbon–oxygen double bond yielding (HGa)5(OiPr)8O (1) as isolable compound. (HGa)5(OiPr)8O may be formally split in to four entities of HGa(OiPr)2 and one entity HGaO. The inner atomic skeleton of 1 is a novel Ga5O9 heterocluster with gallium atoms occupying the corners of a distorted trigonal bi-pyramid, an oxygen atom in the center and the remaining alcoholate oxygen atoms bridging eight of the nine edges of the bi-pyramid (X-ray diffraction analysis). Potassium indium alkoxide KIn(OtBu)4 has been used to synthesize several new compounds like In4(OtBu)8(C5H4)2 (2), (py)2CuIn(OtBu)4 (3), and [CuIn(OtBu)4]2 (4) by reaction with TiCl2cp2 (2) and CuCl (3, 4). All compounds were characterized by spectroscopic means and by X-ray structure analyses revealing novel polycyclic structures.

Hydrogels are normally isotropic and weak, in contrast to their natural analogs that possess hierarchically oriented structure and excellent mechanical properties. Inspired by the unique structure of natural materials, we develop an approach for preparing highly anisotropic hydrogels with programmable oriented polymer structure and extraordinary mechanical properties. Our method is based on a novel welding technique for stretched cellulose hydrogel films, in which interfacial reconfiguration occurs, allowing full integration without compromising the highly aligned polymer orientation. We demonstrate the versatility of this method by fabricating four types of anisotropic tough multilayer hydrogels with differently oriented hierarchies: parallel lamination (‖), orthogonal lamination (⊥), axial rolling, and concentric rolling. These high-water-content hydrogels (∼68 wt%) exhibit extremely high anisotropy (birefringence ≥0.006, the highest reported for hydrogels) and superior mechanical properties (Young's modulus of ∼140 MPa, tensile strength of ∼47 MPa, and work of extension of ∼20 MJ m−3). Moreover, these hydrogels also show interesting anisotropic electrical conductivity and asymmetric shape deformation. Because this method is easy to apply and offers flexibility in designing complex hierarchical hydrogel structures, our work opens a new window to designing novel hydrogel materials for engineering and biomedical applications.

The mechanical properties (e.g., modulus and strength) of conventional tough hydrogels are considerably inferior to those required for practical load-bearing applications. However, developing hydrogels with a combination of superior mechanical properties such as stiffness, strength, and toughness is very challenging. Herein, we propose a new design strategy based on the synergistic effect of hydrophobic/hydrophilic components to fabricate novel hydrogels with superior mechanical properties. Both hydrophobic and hydrophilic monomers were integrated into hydrogels using a simple two-step fabrication process, which led to the formation of a randomly distributed interconnected 3D structure of hard-phase and soft-phase regions comprising hydrophobic-rich and hydrophilic-rich components, respectively. The 3D structure of hard-phase regions imparted exceptional stiffness and strength, whereas soft-phase regions provided sacrificial bonds to achieve stretchability and toughness. Different hydrophobic monomers with widely variable extents of hydrophobicity were used. The obtained results indicated that hydrogels based on benzene-containing hydrophobic monomers and exhibiting a higher-than-ambient glass transition temperature can show superior mechanical properties. Highly water-stable physical hydrogels with water contents of 50–60 wt.% and exceptionally high Young’s modulus (150–280 MPa), tensile strength (7–17 MPa), and fracture energy (6680–7450 J/m2) were developed; these values are far superior to those of single-component hydrogels and tough hydrogels reported to date. This combination of superior properties, reported here for the first time, is expected to significantly broaden the application of hydrogels. The proposed strategy is quite general and offers further opportunities to develop diverse ultra-stiff, strong, and tough functional hydrogels using suitable monomer combinations.

The handling of droplets in a controlled manner is essential to numerous technological and scientific applications. In this work, we present a new open-surface platform for droplet manipulation based on an array of bendable nozzles that are dynamically controlled by a magnetic field. The actuation of these nozzles is possible thanks to the magnetically responsive elastomeric composite which forms the tips of the nozzles; this is fabricated with Fe3O4 microparticles embedded in a polydimethylsiloxane matrix. The transport, mixing, and splitting of droplets can be controlled by bringing together and separating the tips of these nozzles under the action of a magnet. Additionally, the characteristic configuration for droplet mixing in this platform harnesses the kinetic energy from the feeding streams; this provided a remarkable reduction of 80% in the mixing time between drops of liquids about eight times more viscous than water, i.e., 6.5 mPa/s, when compared against the mixing between sessile drops of the same fluids

Conductive hydrogels are attracting increasing attention owing to their great potential for applications in flexible devices. For practical use, these high-water-content materials should not only show good conductivity but also be strong, stretchable, tough, and elastic. Herein, we describe a class of novel conductive tough hydrogels based on strong staggered Fe3+-carboxyl coordinating interactions. They are made from copolymers of acrylamide and N-acryloyl glutamic acid, a bidentate-based comonomer. The design of the staggered structure of Fe3+ and bidentate units is expected to enable energy dissipation and also results in a synergetic effect of two binding sites for fast self-recovery. We demonstrate that the equilibrated hydrogels with a water content of 53 wt % exhibit superior mechanical properties (e.g., highest tensile strength, 12.1 MPa; Young’s modulus, 36.1 MPa; work of extension, 42.1 MJ m–3; fracture energy, 10,691 J m–2; compressive strength, 65.1 MPa at 98% strain without a macroscopic fracture) compared to the ion-coordinated hydrogels reported to date, including elasticity at small strain, fast self-recoverability at room temperature (∼25 °C), a high dielectric constant (k = 341–1395 at 100 kHz), and good electrical conductivity (0.0018–0.024 S cm–1). Given their extraordinary overall characteristics, we envision their potential applications in flexible electronic devices.

The development of simple and effective tools for selective ratiometric detection of hypochlorite (ClO−) is one of the most important goals for elucidating the biofunction of ClO− in associated diseases. However, most developmental probes suffer from the notorious aggregation-caused quenching (ACQ) effect that greatly limits their applications. Herein, we report on novel aggregation-induced emission dots (AIED) for ratiometric detection of ClO− via a co-precipitation strategy. The AIED nanoprobe displayed a ratiometric signal output, which was more promising to minimize the bad environmental factors and simultaneously avoided the ACQ effect. Notably, amphiphilic block copolymer endowed the nanoprobe with stable water dispersibility and easy modification. The as-prepared AIED probe exhibited high sensitivity (~ 89 nM), high selectivity, outstanding photostability, and prominent long-term fluorescence stability. Furthermore, the as-prepared AIED was applied for the visualized fluorescence detection of ClO− and further utilized to detect ClO− in real samples. We expect the nanoprobe to be an outstanding tool to understand ClO−-associated diseases.

Selective crystallization represents one of the most economical and convenient methods to provide large-scale optically pure chiral compounds. Although significant development has been achieved since Pasteur’s separation of sodium ammonium tartrate in 1848, this method is still fundamentally low efficient (low transformation ratio or high labor). Herein, we describe an enantiomer-selective-magnetization strategy for quantitatively separating the crystals of conglomerates by using a kind of magnetic nano-splitters. These nano-splitters would be selectively wrapped into the S-crystals, leading to the formation of the crystals with different physical properties from that of R-crystals. As a result of efficient separation under magnetic field, high purity chiral compounds (99.2 ee% for R-crystals, 95.0 ee% for S-crystals) can be obtained in a simple one-step crystallization process with a high separation yield (95.1%). Moreover, the nano-splitters show expandability and excellent recyclability. We foresee their great potential in developing chiral separation methods used on different scales.

Abstract Controllable stabilization of liquids on interfaces is emerging as a novel method to mediate surface properties. Here, the fast, stimuli-responsive liquid release from dynamic polymer coatings is described to mediate surface slipperiness and optical performance. These polymer coatings consist of a slippery liquid-locked rough surface and a liquid-supplied bottom layer storing the liquid in embedded droplets. They are prepared by a simple one-pot casting of a solution of cross-linkable polymer and silicone oil in tetrahydrofuran. It is demonstrated that upon mechano-, solvent-, or thermo-stimulation, the liquid stored in the bottom layer is released altering both surface slipperiness and optical properties of the coatings.