Impact of wettability onto the growth of air bubbles at micro-cavities on silicon wafers: Experiments, simulations, and analytical solutions.

Hypothesis: The surface wettability influences the oversaturation-driven growth of gas bubbles on the surface via the contact angle. Larger contact angles on hydrophobic surfaces compared to hydrophilic ones lead to faster growth of bubbles nucleating at microcavities of identical size.

Experiments: Cylindric micro-cavities were etched in silicon wafers as nucleation sites.

Functionalization of Ti64 via Direct Laser Interference Patterning and Its Influence on Wettability and Oxygen Bubble Nucleation.

The nucleation of bubbles on solid surfaces is an important phenomenon in nature and technological processes like electrolysis. During proton-exchange membrane electrolysis, the nucleation and separation of the electrically nonconductive oxygen in the anodic cycle plays a crucial role to minimize the overpotential it causes in the system. This increases the efficiency of the process, making renewable energy sources and the "power-to-gas" strategy more viable.

Hydrogen Bubble Size Distribution on Nanostructured Ni Surfaces: Electrochemically Active Surface Area Versus Wettability.

Emerging manufacturing technologies make it possible to design the morphology of electrocatalysts on the nanoscale in order to improve their efficiency in electrolysis processes. The current work investigates the effects of electrode-attached hydrogen bubbles on the performance of electrodes depending on their surface morphology and wettability. Ni-based electrocatalysts with hydrophilic and hydrophobic nanostructures are manufactured by electrodeposition, and their surface properties are characterized.

Electrolysis in reduced gravitational environments: current research perspectives and future applications.

Electrochemical energy conversion technologies play a crucial role in space missions, for example, in the Environmental Control and Life Support System (ECLSS) on the International Space Station (ISS). They are also vitally important for future long-term space travel for oxygen, fuel and chemical production, where a re-supply of resources from Earth is not possible. Here, we provide an overview of currently existing electrolytic energy conversion technologies for space applications such as proton exchange membrane (PEM) and alkaline electrolyzer systems.

On the growth regimes of hydrogen bubbles at microelectrodes.

The growth of single hydrogen bubbles at micro-electrodes is studied in an acidic electrolyte over a wide range of concentrations and cathodic potentials. New bubble growth regimes have been identified which differ in terms of whether the bubble evolution proceeds in the presence of a monotonic or oscillatory variation in the electric current and a carpet of microbubbles underneath the bubble. Key features such as the growth law of the bubble radius, the dynamics of the microbubble carpet, the onset time of the oscillations and the oscillation frequencies have been characterized as a function of the concentration and electric potential.

Force balance of hydrogen bubbles growing and oscillating on a microelectrode.

Hydrogen evolution in acidic aqueous electrolytes was recently found to be characterized by a carpet of microbubbles covering the microelectrode and feeding the growth of the main bubbles by coalescence. Besides this, oscillatory behavior of the main bubbles was observed prior to departure. Extending earlier studies, this work delivers the forces acting on the main bubble more accurately by taking into account further geometric and electrochemical details measured during experiments.

Dynamics of single hydrogen bubbles at Pt microelectrodes in microgravity.

The dynamics of single hydrogen bubbles electrogenerated in acidic electrolytes at a Pt microelectrode under potentiostatic conditions is investigated in microgravity during parabolic flights. Three bubble evolution scenarios have been identified depending on the electric potential applied and the acid concentration. The dominant scenario, characterized by lateral detachment of the grown bubble, is studied in detail.

Oscillating Hydrogen Bubbles at Pt Microelectrodes.

The dynamics of hydrogen bubbles produced via electrolysis in acidic electrolytes is studied in a combination of experiments and numerical simulations. A transition from monotonic to oscillatory bubble growth is observed after 2/3 of the bubble lifetime, if the electric potential exceeds -3  V. This work analyzes characteristic features of the oscillations in terms of bubble geometry, the thickness of the microbubble carpet, and the oscillation frequency.

Cytocompatible, Injectable, and Electroconductive Soft Adhesives with Hybrid Covalent/Noncovalent Dynamic Network.

Synthetic conductive biopolymers have gained increasing interest in tissue engineering, as they can provide a chemically defined electroconductive and biomimetic microenvironment for cells. In addition to low cytotoxicity and high biocompatibility, injectability and adhesiveness are important for many biomedical applications but have proven to be very challenging. Recent results show that fascinating material properties can be realized with a bioinspired hybrid network, especially through the synergy between irreversible covalent crosslinking and reversible noncovalent self-assembly.

Mitigating Meniscus Instabilities in Solution-Sheared Polymer Films for Organic Field-Effect Transistors.

Semiconducting donor-acceptor copolymers are considered to be a promising material class for solution-coated, large-scale organic electronic applications. A large number of works have shown that the best-performing organic field-effect transistors (OFETs) are obtained on low-surface-energy substrates. The meniscus instabilities that occur when coating on such surfaces considerably limit the effective deposition speeds.

Reversibly Assembled Electroconductive Hydrogel via a Host-Guest Interaction for 3D Cell Culture.

The study of cells responding to an electroconductive environment is impeded by the lack of a method, which would allow the encapsulation of cells in an extracellular matrix-like 3D electroactive matrix, and more challengingly, permit a simple mechanism to release cells for further characterization. Herein, we report a polysaccharide-based conductive hydrogel system formed via a β-cyclodextrin-adamantane host-guest interaction. Oxidative polymerization of 3,4-ethylenedioxythiophene (EDOT) in the presence of adamantyl-modified sulfated alginate (S-Alg-Ad) results in bio-electroconductive polymer PEDOT:S-Alg-Ad, which can form hydrogel with poly-β-cyclodextrin (Pβ-CD).

Marangoni convection at electrogenerated hydrogen bubbles.

Electrolytic gas evolution is a fundamental phenomenon occurring in a large number of industrial applications. In these processes gas bubbles are formed at the electrode from a supersaturated solution. Since dissolved gases can change the surface tension, a gas concentration gradient may cause the surface tension to vary locally at the interface of the gas bubble.

Noncovalently Assembled Electroconductive Hydrogel.

Cross-linking biomolecules with electroconductive nanostructures through noncovalent interactions can result in modular networks with defined biological functions and physical properties such as electric conductivity and viscoelasticity. Moreover, the resulting matrices can exhibit interesting features caused by the dynamic assembly process, such as self-healing and molecular ordering. In this paper, we present a physical hydrogel system formed by mixing peptide-polyethylene glycol and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate.

Dynamics of Single Hydrogen Bubbles at a Platinum Microelectrode.

Bubble dynamics, including the formation, growth, and detachment, of single H2 bubbles was studied at a platinum microelectrode during the electrolysis of 1 M H2SO4 electrolyte. The bubbles were visualized through a microscope by a high-speed camera. Electrochemical measurements were conducted in parallel to measure the transient current.

Enrichment of Paramagnetic Ions from Homogeneous Solutions in Inhomogeneous Magnetic Fields.

Applying interferometry to an aqueous solution of paramagnetic manganese ions, subjected to an inhomogeneous magnetic field, we observe an unexpected but highly reproducible change in the refractive index. This change occurs in the top layer of the solution, closest to the magnet. The shape of the layer is in accord with the spatial distribution of the largest component of the magnetic field gradient force.

Design and validation of a bioreactor for simulating the cardiac niche: a system incorporating cyclic stretch, electrical stimulation, and constant perfusion.

To simulate the cardiac niche, a bioreactor system was designed and constructed to incorporate cyclic stretch, rhythmic electrical stimulation, and constant perfusion. The homogeneity of surface strain distribution across the cell culture substrate was confirmed with ARAMIS deformation analysis. The proliferation marker, Ki-67, detected in human umbilical vein endothelial cells and 3-[4,5-dimethyl-thiazol-2-yl]-2,5-diphenyltetrazolium bromide cytotoxicity assay performed on human atrial fibroblasts confirmed biocompatibility of this novel device.