Micrometer‐Scale Porous Buckling Shell Actuators Based on Liquid Crystal Networks

Micrometer‐scale liquid crystal network (LCN) actuators have potential for application areas like biomedical systems, soft robotics, and microfluidics. To fully harness their power, a diversification in production methods is called for, targeting unconventional shapes and complex actuation modes. Crucial for controlling LCN actuation is the combination of macroscopic shape and molecular‐scale alignment in the ground state, the latter becoming particularly challenging when the desired shape is more complex than a flat sheet. Here, one‐step processing of an LCN precursor material in a glass capillary microfluidic set‐up to mold it into thin shells is used, which are stretched by osmosis to reach a diameter of a few hundred micrometers and thickness on the order of a micrometer, before they are UV crosslinked into an LCN. The shells exhibit radial alignment of the director field and the surface is porous, with pore size that is tunable via the osmosis time. The LCN shells actuate reversibly upon heating and cooling. The decrease in order parameter upon heating induces a reduction in thickness and expansion of surface area of the shells that triggers continuous buckling in multiple locations. Such buckling porous shells are interesting as soft cargo carriers with capacity for autonomous cargo release.     

Sputtered Titanium Carbide Thick Film for High Areal Energy on Chip Carbon‐Based Micro‐Supercapacitors

The areal energy density of on‐chip micro‐supercapacitors should be improved in order to obtain autonomous smart miniaturized sensors. To reach this goal, high surface capacitance electrode (>100 mF cm^?2) has to be produced while keeping low the footprint area. For carbide‐derived carbon (CDC) micro‐supercapacitors, the properties of the metal carbide precursor have to be fine‐tuned to fabricate thick electrodes. The ad‐atoms diffusion process and atomic peening effect occurring during the titanium carbide sputtering process are shown to be the key parameters to produce low stress, highly conductive, and thick TiC films. The sputtered TiC at 10^?3 mbar exhibits a high stress level, limiting the thickness of the TiC‐CDC electrode to 1.5 µm with an areal capacitance that is less than 55 mF cm^?2 in aqueous electrolyte. The pressure increase up to 10^?2 mbar induces a clear reduction of the stress level while the layer thickness increases without any degradation of the TiC electronic conductivity. The volumetric capacitance of the TiC‐CDC electrodes is equal to 350 F cm^?3 regardless of the level of pressure. High values of areal capacitance (>100 mF cm^?2) are achieved, whereas the TiC layer is relatively thick, which paves the way toward high‐performance micro‐supercapacitors.     

Synthesis of a porphyrin-fullerene pinwheel

We disclose the synthesis of a porphyrin-fullerene pinwheel that was subsequently observed by scanning tunneling microscopy. The molecule was designed to further our understanding of fullerene-surface interactions, directional control, and surface-rolling versus pivoting capabilities of this class of nanomachines. The inner porphyrin provides the square planar configuration that might lead to realization of the pinwheel spiraling motion on surfaces.     

The electronic structure and adsorption geometry of L-histidine on Cu(110)

The adsorption of L-histidine on clean and oxygen-covered Cu(110) surfaces has been studied by soft X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The valence band spectra, carbon, nitrogen and oxygen 1 s XPS and N K edge absorption spectra were measured for submonolayer, monolayer, and multilayer films. The spectra provide a detailed picture of the electronic structure and adsorption geometry at each coverage. In the monolayer, the histidine molecules are randomly oriented, in contrast to the submonolayer regime, where the molecules are coordinated to the copper surface with the imidazole functional group nearly parallel to, and strongly interacting with, the surface. The pi*/sigma* intensity ratio in NEXAFS spectra at the nitrogen edge varies strongly with angle, showing the imidazole ring is oriented. Adsorption models are proposed.     

Intermolecular vibrational coherence in the bacteriochlorophyll proteins B777 and B820 from Rhodospirillum rubrum

The low-frequency vibrational coherence in the bacteriochlorophyll (BChl)-containing subunit proteins B777 and B820 from the LH1 light-harvesting complex isolated from Rhodospirillum rubrum G9 exhibits rapidly damped modulation components arising from intermolecular, formally nonbonding interactions between the BChl macrocycle and polar groups in the surrounding detergent or protein. The vibrational coherence observed in the monomeric B777 system resembles that observed previously with BChl in acetone because it contains a pair of broad overlapping line shapes with a mean frequency of 191 cm(-1), but the 10:1 intensity ratio of the librational and translational components is distinctive of the motions of the polar head groups in the nonionic detergent micelle that solvates the BChl macrocycle. In contrast, the vibrational coherence observed with the dimeric B820 complex is almost 20 times weaker in intensity and exhibits narrower line shapes and lower average frequencies than observed in B777. The structure of the B820 complex sterically protects the pair of BChl macrocycles from the surrounding solvent, so modulation components assigned to intrinsic interactions between the BChl and the protein and between the pair of BChl's are revealed. A relatively well-ordered interaction between the BChl macrocycle and a tryptophan residue in each alpha-helical polypeptide accounts for a 28 cm(-1) component with a narrow line shape, but most of the intensity arises from a broader 46 cm(-1) component that is assigned to the interaction between the paired BChl macrocycles. The breadth of the line shape for this component is a measure of the disorder in the ensemble of B820 subunits. The results support the hypothesis that the excited-state vibrational dynamics and the optical and/or Marcus charge-transfer reorganization energies of BChl in photosynthetic light-harvesting proteins and reaction centers are strongly controlled by van der Waals modes with neighboring molecules, with dominant contributions to the intermolecular potential arising from the London dispersion and dipole-dipole interactions.     

Metal ion reactive thin films using spray electrostatic LbL assembly

By using the spray-layer-by-layer (Spray-LbL) technique, the number of metal counterions trapped within LbL coatings is significantly increased by kinetically freezing the film short of equilibrium, potentially limiting interchain penetration and forcing chains to remain extrinsically compensated to a much greater degree than observed in the traditional dipped LbL technique. The basis for the enhanced entrapment of metal ions such as Cu2+, Fe2+, and Ag+ is addressed, including the equilibrium driving force for extrinsic compensation by soft versus hard metal ions and the impact of Spray-LbL on the kinetics of polymer-ion complexation. These polymer-bound metal-ion coatings are also demonstrated to be effective treatments for air filtration, functionalizing existing filters with the ability to strongly bind toxic industrial compounds such as ammonia or cyanide gases, as well as chemical warfare agent simulants such as chloroethyl ethyl sulfide. On the basis of results reported here, future work could extend this method to include other toxic soft-base ligands such as carbon monoxide, benzene, or organophosphate nerve agents.     

Photophysical characterization of a highly conjugated bipyridyl-based dye synthesized by a unique two-step approach

In this article, we present a new and simple, yet efficient, two-step approach to synthesize 4,4'-bis(dibutylaminostyrylstyryl)-2,2'-bipyridine with high yield, as well as its linear and nonlinear optical characterizations in THF and toluene solutions. We show that its one- and two-photon absorption spectra are similar in both solvents. Nevertheless, the relaxation processes of this compound exhibit dependence on the solvent polarity. The one- and two-photon induced fluorescence signal of this molecule in solution reveals that its excited state is highly stabilized in THF solution rather than in toluene. Analysis of the fluorescence quantum yield, lifetime, and radiative and nonradiative decay rates are in agreement with Lippert's model for solute-solvent interactions. The optical measurements demonstrate that this dye is a promising candidate for multiphoton fluorescence imaging, optical limiting, and dye lasers.