Preservation of Superhydrophobic and Superoleophobic Properties upon Wear Damage

Superhydrophobicity and self-cleaning require a combination of surface topography and low-energy surfaces, where mechanical damage of the topography or contamination with oils lead to loss of the nonwetting properties. We show that such vulnerability can be solved by superamphiphobic (i.e., both superhydrophobic and superoleophobic) surfactant-coated aerogel surfaces. Using silica aerogels as model materials, the self-similar network structure allows fresh re-entrant surface topographies even after removal of the uppermost layer upon mechanical abrasion, and superoleophobicity suppresses oil contamination. Given the recent progress toward mechanically strong aerogels, we foresee that the concept can open routes for robust self-cleaning coating technologies

Preservation of Superhydrophobic and Superoleophobic Properties upon Wear Damage

Superhydrophobicity and self-cleaning require a combination of surface topography and low-energy surfaces, where mechanical damage of the topography or contamination with oils lead to loss of the nonwetting properties. We show that such vulnerability can be solved by superamphiphobic (i.e., both superhydrophobic and superoleophobic) surfactant-coated aerogel surfaces. Using silica aerogels as model materials, the self-similar network structure allows fresh re-entrant surface topographies even after removal of the uppermost layer upon mechanical abrasion, and superoleophobicity suppresses oil contamination. Given the recent progress toward mechanically strong aerogels, we foresee that the concept can open routes for robust self-cleaning coating technologies

Guest-Induced Folding of the <i>N</i>‑Benzyl Substituents in an Ammonium Resorcinarene Chloride and the Formation of a Halogen-Bonded Dimer of Capsules

In methanol, <i>N</i>-benzyl ammonium resorcinarene chloride (Bn-NARCl) crystallizes as a solvate with the benzyl groups oriented in an open flower-like manner parallel to the cation–anion seam. 1,4-Dioxane as guest triggers a “semi-closed” single-molecule capsule with two benzyl “arms” enclosing the guest. The introduction of halogen bond (XB) donor 1,4-diiodoperfluorobutane (1,4-DIOFB) additionally folds the remaining two benzyl arms thus resulting in a fully closed capsule. Two 1,4-DIOFB molecules bridge two such Bn-NARCl capsules, forming a 2:2:2 XB held dimeric assembly of single-molecule capsules. The peculiar behavior was not observed in the bromide analog under similar experimental conditions. The studies were performed in solid state by X-ray single crystal crystallography, and MM level theoretical calculations

Direct Laser Writing of Photostable Fluorescent Silver Nanoclusters in Polymer Films

Metal nanoclusters consist of a few to a few hundred atoms and exhibit attractive molecular properties such as ultrasmall size, discrete energy levels, and strong fluorescence. Although patterning of these clusters down to the micro- or nanoscale could lead to applications such as high-density data storage, it has been reported only for inorganic matrices. Here we present submicron-scale mask-free patterning of fluorescent silver nanoclusters in an organic matrix. The nanoclusters were produced by direct laser writing in poly(methacrylic acid) thin films and exhibit a broadband emission at visible wavelengths with photostability that is superior to that of Rhodamine 6G dye. This fabrication method could open new opportunities for applications in nanophotonics like imaging, labeling, and metal ion sensing. We foresee that this method can be further applied to prepare other metal nanoclusters embedded in compositionally different polymer matrices

Simple and Efficient Separation of Atomically Precise Noble Metal Clusters

There is an urgent need for accessible purification and separation strategies of atomically precise metal clusters in order to promote the study of their fundamental properties. Although the separation of mixtures of atomically precise gold clusters Au₂₅L₁₈, where L are thiolates, has been demonstrated by advanced separation techniques, we present here the first separation of metal clusters by thin-layer chromatography (TLC), which is simple yet surprisingly efficient. This method was successfully applied to a binary mixture of Au₂₅L₁₈ with different ligands, as well as to a binary mixture of different cluster cores, Au₂₅ and Au₁₄₄, protected with the same ligand. Importantly, TLC even enabled the challenging separation of a multicomponent mixture of mixed-monolayer-protected Au₂₅ clusters with closely similar chemical ligand compositions. We anticipate that the realization of such simple yet efficient separation technique will progress the detailed investigation of cluster properties

Bamboo-like Chained Cavities and Other Halogen-Bonded Complexes from Tetrahaloethynyl Cavitands with Simple Ditopic Halogen Bond Acceptors

Halogen bonding provides a useful complement to hydrogen bonding and metal-coordination as a tool for organizing supramolecular systems. Resorcinarenes, tetrameric bowl-shaped cavitands, have been previously shown to function as efficient scaffolds for generating dimeric capsules in both solution and solid-phase, and complicated one-, two-, and three-dimensional frameworks in the solid phase. Tetrahaloethynyl resorcinarenes (bromide and iodide) position the halogen atoms in a very promising “crown-like” orientation for acting as organizing halogen-bond donors to help build capsules and higher-order networks. Symmetric divalent halogen bond acceptors including bipyridines, 1,4-dioxane, and 1,4-diazabicyclo[2.2.2]­octane are very promising halogen bond accepting partners for creating these systems. This report describes the complex structures arising from combining these various systems including self-included dimers, herringbone-packed architectures enclosing medium (186 ų) cavities, and a very intriguing bamboo-like one-dimensional rod with large (683 ų) cavities between adjacent dimeric units. These various structures, all organized through host–host, host–acceptor, and host–solvent interactions highlight the emergent complexity of these types of complexes. As halogen bonds are weaker than hydrogen-bonds, the resulting architectures are harder to predict, and these results provide additional insight into the parameters requiring consideration when designing crystalline supramolecular systems using halogen-bonds as the core organizing principle

Oscillating Ferrofluid Droplet Microrheology of Liquid-Immersed Sessile Droplets

The damped oscillations of liquid-immersed ferrofluid sessile droplets were studied with high-speed imaging experiments and analytical modeling to develop a novel microrheology technique. Droplet oscillations were induced with an external magnetic field, thereby avoiding transients in the resulting vibrational response of the droplet. By following the droplet relaxation with a high-speed camera, the frequency and relaxation time of the damped harmonic oscillations were measured. We extend upon existing analytical theories to describe our liquid-immersed sessile droplet system, and directly quantify the droplet relaxation with the viscosity of the internal and external fluid as well as the interfacial tension between these. The easily controllable magnetic droplets make our oscillating ferrofluid droplet technique a potential candidate for high-throughput microrheology and tensiometry in the future

Mixed-Monolayer-Protected Au₂₅ Clusters with Bulky Calix[4]arene Functionalities

Although various complex, bulky ligands have been used to functionalize plasmonic gold nanoparticles, introducing them to small, atomically precise gold clusters is not trivial. Here, we demonstrate a simple one-pot procedure to synthesize fluorescent magic number Au₂₅ clusters carrying controlled amounts of bulky calix[4]­arene functionalities. These clusters are obtained from a synthesis feed containing binary mixtures of tetrathiolated calix[4]­arene and 1-butanethiol. By systematic variation of the molar ratio of ligands, clusters carrying one to eight calixarene moieties were obtained. Structural characterization reveals unexpected binding of the calix[4]­arenes to the Au₂₅ cluster surface with two or four thiolates per moiety

Superhydrophobic Paper from Nanostructured Fluorinated Cellulose Esters

The development of economically and ecologically viable strategies for superhydrophobization offers a vast variety of interesting applications in self-cleaning surfaces. Examples include packaging materials, textiles, outdoor clothing, and microfluidic devices. In this work, we produced superhydrophobic paper by spin-coating a dispersion of nanostructured fluorinated cellulose esters. Modification of cellulose nanocrystals was accomplished using 2<i>H</i>,2<i>H</i>,3<i>H</i>,3<i>H</i>-perfluorononanoyl chloride and 2<i>H</i>,2<i>H</i>,3<i>H</i>,3<i>H</i>-perfluoroundecanoyl chloride, which are well-known for their ability to reduce surface energy. A stable dispersion of nanospherical fluorinated cellulose ester was obtained by using the nanoprecipitation technique. The hydrophobized fluorinated cellulose esters were characterized by both solid- and liquid-state nuclear magnetic resonance, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and contact angle measurements. Further, we investigated the size, shape, and structure morphology of nanostructured fluorinated cellulose esters by dynamic light scattering, scanning electron microscopy, and X-ray diffraction measurements

Oscillating Ferrofluid Droplet Microrheology of Liquid-Immersed Sessile Droplets

The damped oscillations of liquid-immersed ferrofluid sessile droplets were studied with high-speed imaging experiments and analytical modeling to develop a novel microrheology technique. Droplet oscillations were induced with an external magnetic field, thereby avoiding transients in the resulting vibrational response of the droplet. By following the droplet relaxation with a high-speed camera, the frequency and relaxation time of the damped harmonic oscillations were measured. We extend upon existing analytical theories to describe our liquid-immersed sessile droplet system, and directly quantify the droplet relaxation with the viscosity of the internal and external fluid as well as the interfacial tension between these. The easily controllable magnetic droplets make our oscillating ferrofluid droplet technique a potential candidate for high-throughput microrheology and tensiometry in the future