Mechanical properties of flexible films, for example surface strain of largely bending films, are key to design of stretchable electronic devices, wearable biointegrated devices, and soft microactuators/robots. However, existing methods are mainly based on strain-gauge measurements that require miniaturized array sensors, lead wires, and complicated calibrations. Here we introduce a facile method, based on surface-labelled gratings, for two-dimensional evaluation of surface strains in largely bending films. With this technique, we demonstrate that soft-matter mechanics can be distinct from the mechanics of hard materials. In particular, liquid-crystalline elastomers may undergo unconventional bending in three dimensions, in which both the inner and outer surfaces of the bending film are compressed. We also show that this method can be applied to amorphous elastomeric films, which highlights the general importance of this new mechanical evaluation tool in designing soft-matter-based electronic/photonic as well as biointegrated materials.
We report the development of a silicon nanowire array-stabilized palladium nanoparticle catalyst, SiNA-Pd. Its use in the palladium-catalyzed Mizoroki-Heck reaction, the hydrogenation of an alkene, the hydrogenolysis of nitrobenzene, the hydrosilylation of an ?,?-unsaturated ketone, and the C-H bond functionalization reactions of thiophenes and indoles achieved a quantitative production with high reusability. The catalytic activity reached several hundred-mol ppb of palladium, reaching a TON of 2?000?000.
Large-area homeotropic columnar ordering of ?-conjugated discotic liquid crystals (LCs) is crucial for certain device applications but generally hard to achieve. Here we report polymeric o-phenylene octamer poly-1 and its monomer 1 as the first surface modifiers for homeotropic columnar order of a variety of discotic LCs up to a macroscopic length scale. Their octameric o-phenylene parts are known to fold helically into a cylinder that is reminiscent of a ?-stacked column of discotic LCs. Through-view X-ray diffraction patterns of 1 suggested that this molecule adheres to the glass substrate and directs its cylindrical axis perpendicular to the glass surface. This "face-on" orientation likely nucleates the homeotropic columnar order of discotic LC materials.
A direct electrochemistry and intramolecular electron transfer of multicopper oxidases are of a great importance for the fabrication of these enzyme-based bioelectrochemical-devices. Ascorbate oxidase from Acremonium sp. (ASOM) has been successfully immobilized via a chemisorptive interaction on the l-cysteine self-assembled monolayer modified gold electrode (cys-SAM/AuE). Thermodynamics and kinetics of adsorption of ASOM on the cys-SAM/AuE were studied using cyclic voltammetry. A well-defined redox wave centered at 166±3mV (vs. Ag?AgCl?KCl(sat.)) was observed in 5.0mM phosphate buffer solution (pH7.0) at the fabricated ASOM electrode, abbreviated as ASOM/cys-SAM/AuE, confirming a direct electrochemistry, i.e., a direct electron transfer (DET) between ASOM and cys-SAM/AuE. The direct electrochemistry of ASOM was further confirmed by taking into account the chemical oxidation of ascorbic acid (AA) by O2 via an intramolecular electron transfer in the ASOM as well as the electrocatalytic oxidation of AA at the ASOM/cys-SAM/AuE. Thermodynamics and kinetics of the adsorption of ASOM on the cys-SAM/AuE have been elaborated along with its direct electron transfer at the modified electrodes on the basis of its intramolecular electron transfer and electrocatalytic activity towards ascorbic acid oxidation and O2 reduction. ASOM saturated surface area was obtained as 2.41×10(-11)molcm(-2) with the apparent adsorption coefficient of 1.63×10(6)Lmol(-1). The ASOM confined on the cys-SAM/AuE possesses its essential enzymatic function.
We perform large-scale molecular dynamics simulations to measure the contact-angle hysteresis for a nanodroplet of water placed on a nanopillared surface. The water droplet can be in either the Cassie state (droplet being on top of the nanopillared surface) or the Wenzel state (droplet being in contact with the bottom of nanopillar grooves). To measure the contact-angle hysteresis in a quantitative fashion, the molecular dynamics simulation is designed such that the number of water molecules in the droplets can be systematically varied, but the number of base nanopillars that are in direct contact with the droplets is fixed. We find that the contact-angle hysteresis for the droplet in the Cassie state is weaker than that in the Wenzel state. This conclusion is consistent with the experimental observation. We also test a different definition of the contact-angle hysteresis, which can be extended to estimate hysteresis between the Cassie and Wenzel state. The idea is motivated from the appearance of the hysteresis loop typically seen in computer simulation of the first-order phase transition, which stems from the metastability of a system in different thermodynamic states. Since the initial shape of the droplet can be controlled arbitrarily in the computer simulation, the number of base nanopillars that are in contact with the droplet can be controlled as well. We show that the measured contact-angle hysteresis according to the second definition is indeed very sensitive to the initial shape of the droplet. Nevertheless, the contact-angle hystereses measured based on the conventional and new definition seem converging in the large droplet limit.
Free-standing, ultralong (up to several millimeters) nanobelts of gold, silver, and copper were fabricated by a template approach. Firstly, a metal nanofin array was prepared on a substrate via metal nanocoating of the template surface and selective removal of the metal top layer and template. Electroless plating and sputtering were employed for the metal nanocoating. In this approach, the minimum width and thickness of the Au nanobelt were 95 and 30 nm, respectively. Systematic control of the nanobelt width (from 95 to 350 nm) was successfully achieved by adjusting the template height. Free-standing nanobelts of several millimeters in length were fabricated and maintained their unique structure and alignment, even on a mesh grid.
We propose a simple, precise, and wafer-scale fabrication technique for Au double nanopillar (DNP) arrays with nanogaps of several tens of nanometers. An Au DNP was simply constructed by alternately laminating thin layers of Au and polymer on a template and selectively removing the thin layers. This DNP array was expected to exhibit a specific plasmonic property induced by its narrow gap. When measuring the refractive index sensitivity (RIS), Au DNP arrays with 33 nm gaps exhibited a high RIS of 1075 nm RIU(-1) and showed a higher sensor figure of merit than the alternative structures, which did not have a nanogap structure but had almost the same surface area. This indicated that the enhanced plasmon electromagnetic field induced by the nanogap structure improved sensor performance. Our fabrication technique and the optical properties of the nanogap structure will provide useful information for developing new plasmonic applications with nanogap structures.
We performed molecular dynamics (MD) simulations to investigate equilibrium behavior of urea-water binary droplets on flat (graphitic) and pillared surfaces. The contact angles as a function of urea concentration on the flat surface are computed. It is found that the contact angle decreases as the urea concentration increases. At the equilibrium state, the urea molecules in the droplet tend to be located near the hydrophobic graphite surface. This behavior is consistent with the denaturing effects of urea in protein solutions. We also performed MD simulations of collision between a urea-water droplet and the pillared surface to examine the tendency for the droplet being in the Cassie state (droplet staying on top of the pillared surface) or in the Wenzel state (droplet staying at the bottom of the pillared surface), at various urea concentrations.
A free-standing ultrathin film of a poly(vinyl alcohol) (PVA)/titania (TiO2) composite was prepared by spin coating. The thickness of the film was adjusted to 30-50 nm by changing the spin-coating speed and the concentrations of PVA and the TiO2 precursor. A template molecule, (4-phenylazo)benzoic acid (4PABA), was introduced into the film as a mixture in the TiO2 precursor and was removed after film formation by dipping the film in aq NH3 (1%). Aqueous solutions of tetraphenylporphyrin tetrasulfonic acid (TPPS), 4PABA, and sodium benzoate (SB) were filtered through this film, and the concentrations of these compounds in the filtered solution were monitored by UV-vis absorption measurements. The filtered TPPS solution was colorless, and its absorbance at 413 nm was 8% that of the original solution. In contrast, almost 100% of SB and 28.4% of 4PABA were passed through the film. The ultrathin TiO2/PVA film obtained without imprinting with 4PABA had no cavities, and aqueous solutions did not pass through this film. Therefore, it was concluded that the nonimprinted film was defect free and that imprinting of the template molecule in the film resulted in the formation of a size-selective channel across a 40 nm thickness.
Water droplets on rugged hydrophobic surfaces typically exhibit one of the following two states: (i) the Wenzel state [Wenzel RN (1936) Ind Eng Chem 28:988-994] in which water droplets are in full contact with the rugged surface (referred as the wetted contact) or (ii) the Cassie state [Cassie, ABD, Baxter S (1944) Trans Faraday Soc 40:546-551] in which water droplets are in contact with peaks of the rugged surface as well as the "air pockets" trapped between surface grooves (the composite contact). Here, we show large-scale molecular dynamics simulation of transition between Wenzel state and Cassie state of water droplets on a periodic nanopillared hydrophobic surface. Physical conditions that can strongly affect the transition include the height of nanopillars, the spacing between pillars, the intrinsic contact angle, and the impinging velocity of water nanodroplet ("raining" simulation). There exists a critical pillar height beyond which water droplets on the pillared surface can be either in the Wenzel state or in the Cassie state, depending on their initial location. The free-energy barrier separating the Wenzel and Cassie state was computed on the basis of a statistical-mechanics method and kinetic raining simulation. The barrier ranges from a few tenths of k(B)T(0) (where k(B) is the Boltzmann constant, and T(0) is the ambient temperature) for a rugged surface at the critical pillar height to approximately 8 k(B)T(0) for the surface with pillar height greater than the length scale of water droplets. For a highly rugged surface, the barrier from the Wenzel-to-Cassie state is much higher than from Cassie-to-Wenzel state. Hence, once a droplet is trapped deeply inside the grooves, it would be much harder to relocate on top of high pillars.
An easy and large-scale fabrication technique of metal fins was used to produce periodic Au fin arrays that realized light confinement in the near-infrared region. Light confinement was revealed by vortex patterns in the optical power flow of an array of high-aspect-ratio fins (height of 1000 nm for a width of 50 nm). The light confinement resulted in sharp dips in the reflectance spectrum of the high-aspect-ratio fin array. The wavelengths of the reflectance dips were found to shift toward higher values when the refractive index of the surrounding medium was increased. Experimental and simulated dip shift values were in good agreement with a demonstrated sensitivity of 580 nm per refractive index unit.
Lipophilic paddlewheel biruthenium complexes [Ru(2)(?-O(2)CR)(3)X](n) (O(2)CR = 3,4,5-tridodecyloxybenzoate, X = Cl, I) self-assemble in organic media to form halogen-bridged coordination polymers. The polymerization is accompanied by spectral changes in ?(RuO,Ru(2)) ? ?*(Ru(2)) and ?(axial ligand) ? ?*(Ru(2)) absorption bands. These polymeric complexes form lyotropic liquid crystals in n-decane at concentrations above ~100 unit mM. The bridging halogen axial ligands (X = Cl or I) exert significant influences on their electronic structures and self-assembling characteristics: the chloride-bridged polymers give hexagonally aligned ordered columnar structure (columnar hexagonal phase, Col(h)), whereas the iodide-bridged polymers form less ordered columnar nematic (Col(n)) phase, as revealed by small-angle X-ray diffraction measurements. Chloro-bridged coordination polymers dispersed in n-decane are thermally intact even at the elevated temperature of 70 °C. In contrast, iodo-bridged polymers show reversible dissociation and reassembly phenomena depending on temperature. These halogen-bridged coordination polymers show unidirectional alignment upon applying alternating current (ac) electric field as investigated by crossed polarizing optical microscopy and scanning electron microscopy. The unidirectionally oriented columns of chloro-bridged polymers are accumulated upon repetitive application of the ac voltage, whereas iodo-bridged coordination polymers show faster and reversible alignment changes in response to turning on-and-off the electric field. The controlled self-assembly of electronically conjugated linear complexes provide a potential platform to design electric field-responsive nanomaterials.
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