Anisotropic Metal Deposition on TiO2 Particles by Electric‐Field‐Induced Charge Separation

Deposition of metals on TiO₂ semiconductor particles (M‐TiO₂) results in hybrid Janus objects combining the properties of both materials. One of the techniques proposed to generate Janus particles is bipolar electrochemistry (BPE). The concept can be applied in a straightforward way for the site‐selective modification of conducting particles, but is much less obvious to use for semiconductors. Herein we report the bulk synthesis of anisotropic M‐TiO₂ particles based on the synergy of BPE and photochemistry, allowing the intrinsic limitations, when they are used separately, to be overcome. When applying electric fields during irradiation, electrons and holes can be efficiently separated, thus breaking the symmetry of particles by modifying them selectively and in a wireless way on one side with either gold or platinum. Such hybrid materials are an important first step towards high‐performance designer catalyst particles, for example for photosplitting of water.     

Void‐Assisted Ion‐Paired Proton Transfer at Water–Ionic Liquid Interfaces

At the water–trihexyl(tetradecyl)phosphonium tris(pentafluoroethyl)trifluorophosphate ([P_14,6,6,6][FAP]) ionic liquid interface, the unusual electrochemical transfer behavior of protons (H⁺) and deuterium ions (D⁺) was identified. Alkali metal cations (such as Li⁺, Na⁺, K⁺) did not undergo this transfer. H⁺/D⁺ transfers were assisted by the hydrophobic counter anion of the ionic liquid, [FAP]^?, resulting in the formation of a mixed capacitive layer from the filling of the latent voids within the anisotropic ionic liquid structure. This phenomenon could impact areas such as proton‐coupled electron transfers, fuel cells, and hydrogen storage where ionic liquids are used as aprotic solvents.     

Electric‐Field‐Induced Viscosity Change of a Nematic Liquid Crystal with Gold Nanoparticles

The electro‐rheological (ER) effect of a composite material consisting of a nematic liquid crystal (LC) and gold nanoparticles covered with mesogenic groups is discussed. The gold nanoparticles are covered by alkyl chains and liquid‐crystalline compounds. The influences of the alkyl‐chain length and the coverage by the alkyl chain and the mesogenic group on the miscibility of the nanoparticles with the LC are investigated by polarizing optical microscopy (POM). The presence of the gold nanoparticles in the nematic LC (5CB) leads to an enhanced ER response compared to that observed for 5CB. The prominent ER effect observed in this study is supported by the two mechanisms proposed, that is, the homogeneous and heterogeneous mechanisms. This study demonstrates the potential of a hybrid system consisting of an LC and gold nanoparticles to improve the ER effect.     

Van der Waals Emulsions: Emulsions Stabilized by Surface‐Inactive,Hydrophilic Particles via van der Waals Attraction

Surface‐inactive, highly hydrophilic particles are utilized to effectively and reversibly stabilize oil‐in‐water emulsions. This is a result of attractive van der Waals forces between particles and oil droplets in water, which are sufficient to trap the particles in close proximity to oil–water interfaces when repulsive forces between particles and oil droplets are suppressed. The emulsifying efficiency of the highly hydrophilic particles is determined by van der Waals attraction between particle monolayer shells and oil droplets enclosed therein and is inversely proportional to the particle size, while their stabilizing efficiency is determined by van der Waals attraction between single particles and oil droplets, which is proportional to the particle size. This differentiation in mechanism between emulsification and stabilization will significantly advance our knowledge of emulsions, thus enabling better control and design of emulsion‐based technologies in practice.     

A Microfluidic Approach to Chemically Driven Assembly of Colloidal Particles at Gas–Liquid Interfaces

Bubbling up : Dissolution of CO₂ bubbles in a suspension of colloidal particles chemically induces the assembly of particles on the surface of shrunken bubbles, and thus yields rapid continuous formation of a colloidal armor. This approach maintains the high colloidal stability of particles in bulk, has increased productivity, and allows the formation of bubbles with precisely controlled dimensions.

     

Electric‐Field Distribution at the End of a Charged Capillary—A Coupling Imaging Study

The electric‐field distribution at the end of a charged capillary system is detected using a scanning electrochemical microscopy (SECM) coupling imaging mode. A theoretical model based on the resistance of solution at the capillary end describes the three‐dimensional distribution of the electric field. The effect of the detection electrode position and separation high voltage on solution potential is observed and analyzed. Results demonstrate that the electric field at the end‐channel shows an isopotential contour changing from a disk shape into a hemispherical shape when leaving the capillary opening. The solution potential decreases along the central axis of the capillary to the detection reservoir. In the same scanning plane, the solution potential decreases along the radial direction. Increase of the separation high voltage results in the increase of the absolute solution potential but does not change the relative spatial electric‐field distribution.     

Hydrogen Evolution at Liquid–Liquid Interfaces

Blowing bubbles : Hydrogen evolution by proton reduction with [(C₅Me₅)₂Fe] occurs at a soft interface between water and 1,2‐dichloroethane (DCE). The reaction proceeds by proton transfer assisted by [(C₅Me₅)₂Fe] across the water–DCE interface with subsequent proton reduction in DCE. The interface essentially acts as a proton pump, allowing hydrogen evolution by directly using the aqueous proton.

     

Metal Deposition at the Liquid–Liquid Interface

Metal nanoparticles are readily formed, with a reasonable degree of size and shape control, using solution‐based reduction methods under ambient conditions. Despite the large number of reports in this field, much of our knowledge of nanoparticle growth is largely empirical, with the relationship between particle form and growth conditions, for example, still not well understood. Many nanoparticle preparation routes actually depend on not one, but two, solution phases, i.e. the syntheses involve reaction or transfer at the liquid–liquid (organic–water) interface. This interface can be polarised electrochemically, an approach that offers promise as a route to better understanding, and ultimately control, of nanoparticle growth.     

Electrochemical Properties of Phospholipid Monolayers at Liquid–Liquid Interfaces

Biomembrane models built at the interface between two immiscible electrolytes (ITIES) are useful systems to study phenomena of biological relevance by means of their electrochemical processes. The unique properties of ITIES allow one either to control or measure the potential difference across the biomimetic membranes. Herein we focus on phospholipid monolayers adsorbed at liquid–liquid interfaces, and besides discussing recent developments on the subject, we describe electrochemical techniques that can be used to get insight on the interfacial processes and electrostatic properties of phospholipid membranes at the ITIES. In particular, we examine the electrochemical and physicochemical properties of (modified) phospholipid monolayers and their interaction with other biologically relevant compounds. The use of liquid–liquid electrochemistry as a powerful tool to characterize drug properties is outlined. Although this review is not a survey of all the work in the field, it provides a comprehensive referencing to current research.     

Laser‐Induced Fluorometry for Capillary Electrophoresis

Laser‐induced fluorometry (LIF) has achieved the detection of single molecules, which ranks it among the most sensitive of detection techniques, whereas capillary electrophoresis (CE) is known as a powerful separation method with resolution that is beyond the reach of many other types of chromatography. Therefore, a coupling of LIF with CE has established an unrivaled analytical technique in terms of sensitivity and resolution. CE‐LIF has demonstrated excellent performance in bioanalytical chemistry for the high‐resolution separation and highly sensitive detection of DNAs, proteins, and small bioactive molecules. This review describes the CE‐LIF methods developed by the author's group that include indirect and direct detection using diode lasers, post‐column derivatization, and Hadamard transformation, as well as applications to the binding assays of specific DNA immunoassays of proteins and to the determination of anticancer drugs.     

Spectroscopic Evidence for Clusters of Like‐Charged Ions in Ionic Liquids Stabilized by Cooperative Hydrogen Bonding

Direct spectroscopic evidence for hydrogen‐bonded clusters of like‐charged ions is reported for ionic liquids. The measured infrared O?H vibrational bands of the hydroxyethyl groups in the cations can be assigned to the dispersion‐corrected DFT calculated frequencies of linear and cyclic clusters. Compensating the like‐charge Coulomb repulsion, these cationic clusters can range up to cyclic tetramers resembling molecular clusters of water and alcohols. These ionic clusters are mainly present at low temperature and show strong cooperative effects in hydrogen bonding. DFT‐D3 calculations of the pure multiply charged clusters suggest that the attractive hydrogen bonds can compete with repulsive Coulomb forces.     

Soft Polymer Janus Nanoparticles at Liquid–Liquid Interfaces

Soft polymeric Janus nanoparticles (JNPs), made from polystyrene‐b‐poly(butadiene)‐b‐poly(methylmethacrylate), PS‐PB‐PMMA, triblock terpolymers, assemble into a monolayer at the water–oil interface to reduce interfacial tension. The extent to which the polymer chains can deform influences the packing density of the JNPs at the interface. The longer the polymer chains are relative to the core, the softer are the JNPs, resulting in a JNPs assembly with a lower initial lateral packing density. The interfacial activity of JNPs can be further tuned by complexation of the PMMA chains with lithium ions that are introduced into the water phase. This work provides a fundamental understanding of soft JNPs packing at the water–oil interface and provides a strategy to tailor the areal density of soft JNPs at liquid–liquid interface, enabling the design of smart responsive structured‐liquid systems.     

Azo Polymer Janus Particles Possessing Photodeformable and Magnetic‐Field‐Responsive Dual Functions

It is of great fundamental and practical significance to endow Janus particles with various field‐responsive properties. In this study, a new strategy with a wide range of application possibilities is developed to fabricate JPs composed of a methacrylate‐based azo polymer, polystyrene, and Fe₃O₄ nanoparticles. The JPs are obtained through microphase separation in a confined volume of the dispersed droplets. The azo polymer and PS are incorporated in JPs in a core‐compartmentalized manner, and Fe₃O₄ are proved to exist in the azo polymer phase. The JPs show responsive movement in the magnetic field and can be easily oriented with the help of the field. By variation of the intersection angle between the particle symmetrical axis and the polarization direction of the linearly polarized laser beam, different deformation modes are feasibly achieved for the JPs. By exploiting the dual‐responsive properties, JPs with designed shapes can be fabricated by exposing the JPs to linearly polarized light.     

Resolving Non‐Specific and Specific Adhesive Interactions of Catechols at Solid/Liquid Interfaces at the Molecular Scale

The adhesive system of mussels evolved into a powerful and adaptive system with affinity to a wide range of surfaces. It is widely known that thereby 3,4‐dihydroxyphenylalanine (Dopa) plays a central role. However underlying binding energies remain unknown at the single molecular scale. Here, we use single‐molecule force spectroscopy to estimate binding energies of single catechols with a large range of opposing chemical functionalities. Our data demonstrate significant interactions of Dopa with all functionalities, yet most interactions fall within the medium–strong range of 10–20 k_BT. Only bidentate binding to TiO₂ surfaces exhibits a higher binding energy of 29 k_BT. Our data also demonstrate at the single‐molecule level that oxidized Dopa and amines exhibit interaction energies in the range of covalent bonds, confirming the important role of Dopa for cross‐linking in the bulk mussel adhesive. We anticipate that our approach and data will further advance the understanding of biologic and technologic adhesives.     

Hydrogen‐Bond‐Selective Phase Transfer of Nanoparticles across Liquid/Gel Interfaces

In the swim : Colloidal nanoparticles coated with polylactide (PLA, red) and poly(ethylene glycol) brushes (PEG, black) can transfer from organic to aqueous phases across liquid/liquid or liquid/gel interfaces during degradation of the PLA coating (see picture: first step), which is driven selectively by the hydrogen bonding of the PEG coating with the aqueous phase (second step).

     

Self‐Assembling Nanoparticles at Surfaces and Interfaces

Nanoparticles are the focus of much attention due to their astonishing properties and numerous possibilities for applications in nanotechnology. For realising versatile functions, assembly of nanoparticles in regular patterns on surfaces and at interfaces is required. Assembling nanoparticles generates new nanostructures, which have unforeseen collective, intrinsic physical properties. These properties can be exploited for multipurpose applications in nanoelectronics, spintronics, sensors, etc. This review surveys different techniques, currently employed and being developed, for assembling nanoparticles in to ordered nanostructures. In this endeavour, the principles and methods involved in the development of assemblies are discussed. Subsequently, different possibilities of nanoparticle‐based nanostructures, obtained in multi‐dimensions, are presented.