Showing papers in "Langmuir in 2014"
TL;DR: This review tracks the various approaches to zwitteration, such as monolayer assemblies and polymeric brush coatings, on micro- to macroscopic surfaces.
Abstract: Coating surfaces with thin or thick films of zwitterionic material is an effective way to reduce or eliminate nonspecific adsorption to the solid/liquid interface. This review tracks the various approaches to zwitteration, such as monolayer assemblies and polymeric brush coatings, on micro- to macroscopic surfaces. A critical summary of the mechanisms responsible for antifouling shows how zwitterions are ideally suited to this task.
699 citations
TL;DR: A more generalized spontaneous imbibitions model is developed by considering the different sizes and shapes of pores, the tortuosity of imbibition streamlines in random porous media, and the initial wetting-phase saturation and test results show that the generalized model can be used to characterize the spontaneous imbIBition behavior of many different porous media.
Abstract: Spontaneous imbibition of wetting liquids in porous media is a ubiquitous natural phenomenon which has received much attention in a wide variety of fields over several decades. Many traditional and recently presented capillary-driven flow models are derived based on Hagen–Poiseuille (H–P) flow in cylindrical capillaries. However, some limitations of these models have motivated modifications by taking into account different geometrical factors. In this work, a more generalized spontaneous imbibition model is developed by considering the different sizes and shapes of pores, the tortuosity of imbibition streamlines in random porous media, and the initial wetting-phase saturation. The interrelationships of accumulated imbibition weight, imbibition rate and gas recovery and the properties of the porous media, wetting liquids, and their interactions are derived analytically. A theoretical analysis and comparison denote that the presented equations can generalize several traditional and newly developed models fr...
476 citations
TL;DR: Biological templates have been used to demonstrate that wickability is the single factor dictating CHF on structured superhydrophilic surfaces and provides a framework for designing and optimizing coatings for further enhancement.
Abstract: While superhydrophilic coatings with enhanced wetting properties have been shown to increase the pool boiling critical heat flux (CHF), the role of nanostructures on its enhancement is not clear. Here, biological templates have been used to demonstrate that wickability is the single factor dictating CHF on structured superhydrophilic surfaces. The flexibility of biotemplating using the Tobacco mosaic virus has been leveraged to create surfaces with varying scales, morphologies, and roughness factors. Their wickabilities have been quantified via the wicked volume flux, a phenomenological parameter analogous to the contact angle, and the role of wickability on CHF has been demonstrated using data from over three dozen individual surfaces. These results are repeatable and independent of the substrate material, surface fouling, structure material, morphology, and contact angle as well as the structure scale. An experimentally validated correlation for CHF has been reported on the basis of the dimensionless wickability. Additionally, the surfaces have achieved a CHF of 257 W/cm(2) for water, representing the highest reported value to date for superhydrophilic surfaces. While the role of wickability on CHF has often been cited anecdotally, this work provides a quantitative measure of the phenomena and provides a framework for designing and optimizing coatings for further enhancement.
373 citations
TL;DR: G/Cu exhibits the highest surface energy immediately after synthesis, and the surface energy decreases after airborne contamination occurs, suggesting the root cause of intrinsically mild polarity of G/Cu surface is discussed.
Abstract: Because of the atomic thinness of graphene, its integration into a device will always involve its interaction with at least one supporting substrate, making the surface energy of graphene critical to its real-life applications. In the current paper, the contact angle of graphene synthesized by chemical vapor deposition (CVD) was monitored temporally after synthesis using water, diiodomethane, ethylene glycol, and glycerol. The surface energy was then calculated based on the contact angle data by the Fowkes, Owens–Wendt (extended Fowkes), and Neumann models. The surface energy of fresh CVD graphene grown on a copper substrate (G/Cu) immediately after synthesis was determined to be 62.2 ± 3.1 mJ/m2 (Fowkes), 53.0 ± 4.3 mJ/m2 (Owens–Wendt) and 63.8 ± 2.0 mJ/m2 (Neumann), which decreased to 45.6 ± 3.9, 37.5 ± 2.3, and 57.4 ± 2.1 mJ/m2, respectively, after 24 h of air exposure. The ellipsometry characterization indicates that the surface energy of G/Cu is affected by airborne hydrocarbon contamination. G/Cu ex...
360 citations
TL;DR: Porous graphitic carbon nitride was synthesized by controllable thermal polymerization of urea in air to form MoS2/C3N4 heterostructures via a facile ultrasonic chemical method and served as electron trapper to extend the lifetime of separated electron-hole pairs.
Abstract: Porous graphitic carbon nitride was synthesized by controllable thermal polymerization of urea in air. Their textural, electrical, and optical properties were tuned by varying the heating rate. The presence of proper residual oxygen in carbon nitride matrix had enhanced light absorption and inhibited the recombination of charge carriers. Furthermore, the MoS2 nanosheets were coupled into the carbon nitride to form MoS2/C3N4 heterostructures via a facile ultrasonic chemical method. The optimized MoS2/C3N4 heterostructure with 0.05 wt % MoS2 showed a reaction rate constant as high as 0.301 min–1, which was 3.6 times that of bare carbon nitride. As analyzed by SEM, TEM, UV–vis absorption, PL and photoelectrochemical measurements, intimate contact interface, extended light response range, enhanced separation speed of charge carriers, and high photocurrent density upon MoS2 coupling led to the photocatalytic promotion of the MoS2/C3N4 heterostructures. In this architecture, MoS2 served as electron trapper to e...
345 citations
TL;DR: The energy barrier in the wetting transition from the Cassie-Baxter state to the Wenzel state was dominated by the competition between the energy barrier and external forces, particularly the Laplace pressure in the present case.
Abstract: The wetting transition from the Cassie–Baxter state to the Wenzel state on textured surfaces was investigated. Nano- to microscale hexagonal pillared lattices were prepared by nanoimprint lithography on fluorinated cycloolefin polymer substrates. The transition was clearly observed for water and some ionic liquids through contact angle measurements and optical microscopy. A simple model clearly demonstrated that the energy barrier in the wetting transition from the Cassie–Baxter state to the Wenzel state was dominated by the competition between the energy barrier and external forces, particularly the Laplace pressure in the present case.
335 citations
TL;DR: This work synthesized mesoporous carbon from pre-cross-linked lignin gel impregnated with a surfactant as the pore-forming agent and activated the carbon through physical and chemical methods to obtain activated mesoporus carbon.
Abstract: We synthesized mesoporous carbon from pre-cross-linked lignin gel impregnated with a surfactant as the pore-forming agent and then activated the carbon through physical and chemical methods to obtain activated mesoporous carbon. The activated mesoporous carbons exhibited 1.5- to 6-fold increases in porosity with a maximum Brunauer–Emmett–Teller (BET) specific surface area of 1148 m2/g and a pore volume of 1.0 cm3/g. Both physical and chemical activation enhanced the mesoporosity along with significant microporosity. Plots of cyclic voltammetric data with the capacitor electrode made from these carbons showed an almost rectangular curve depicting the behavior of ideal double-layer capacitance. Although the pristine mesoporous carbon exhibited a range of surface-area-based capacitance similar to that of other known carbon-based supercapacitors, activation decreased the surface-area-based specific capacitance and enhanced the gravimetric specific capacitance of the mesoporous carbons. A vertical tail in the ...
332 citations
TL;DR: The potential for LIS to reduce drag in laminar flows is demonstrated and the dependence of drag reduction on the ratio of the viscosity of the working fluid to that of the lubricant is elucidated.
Abstract: Lubricant-impregnated surfaces (LIS), where micro/nanotextured surfaces are impregnated with lubricating liquids, have received significant attention for their robust, superslippery properties. In this study, we systematically demonstrate the potential for LIS to reduce drag in laminar flows. We present a scaling model that incorporates the viscosity of the lubricant and elucidates the dependence of drag reduction on the ratio of the viscosity of the working fluid to that of the lubricant. We experimentally validate this dependence in a cone and plate rheometer and demonstrate a drag reduction of 16% and slip length of 18 μm in the case where the ratio of working fluid viscosity to lubricant viscosity is 260.
244 citations
TL;DR: It is suggested that the presence of organic acids (such oxalic or citric acids) plays an important role in the stabilization of iron nanoparticles, and that plants containing such constituents may be more efficacious for the green synthesis of Iron nanoparticles.
Abstract: We report the synthesis and characterization of amorphous iron oxide nanoparticles from iron salts in aqueous extracts of monocotyledonous (Hordeum vulgare) and dicotyledonous (Rumex acetosa) plants. The nanoparticles were characterized by TEM, absorbance spectroscopy, SAED, EELS, XPS, and DLS methods and were shown to contain mainly iron oxide and iron oxohydroxide. H. vulgare extracts produced amorphous iron oxide nanoparticles with diameters of up to 30 nm. These iron nanoparticles are intrinsically unstable and prone to aggregation; however, we rendered them stable in the long term by addition of 40 mM citrate buffer pH 3.0. In contrast, amorphous iron oxide nanoparticles (diameters of 10-40 nm) produced using R. acetosa extracts are highly stable. The total protein content and antioxidant capacity are similar for both extracts, but pH values differ (H. vulgare pH 5.8 vs R. acetosa pH 3.7). We suggest that the presence of organic acids (such oxalic or citric acids) plays an important role in the stabilization of iron nanoparticles, and that plants containing such constituents may be more efficacious for the green synthesis of iron nanoparticles.
243 citations
TL;DR: The results identify a nanopore geometry that is permeable to hydrogen and helium, is significantly less permeability to nitrogen, and is essentially impermeable to methane, thus validating previous suggestions that nanoporous graphene membranes can be used for gas separation.
Abstract: We present an investigation of molecular permeation of gases through nanoporous graphene membranes via molecular dynamics simulations; four different gases are investigated, namely helium, hydrogen, nitrogen, and methane. We show that in addition to the direct (gas-kinetic) flux of molecules crossing from the bulk phase on one side of the graphene to the bulk phase on the other side, for gases that adsorb onto the graphene, significant contribution to the flux across the membrane comes from a surface mechanism by which molecules cross after being adsorbed onto the graphene surface. Our results quantify the relative contribution of the bulk and surface mechanisms and show that the direct flux can be described reasonably accurately using kinetic theory, provided the latter is appropriately modified assuming steric molecule–pore interactions, with gas molecules behaving as hard spheres of known kinetic diameters. The surface flux is negligible for gases that do not adsorb onto graphene (e.g., He and H2), whi...
238 citations
TL;DR: The bioinspired interdigitated pattern is found to outperform the straight hydrophilic-superhydrophilic pattern design, particularly under higher humidity conditions in the presence of noncondensable gases (NCG), a condition that is more challenging for maintaining sustained DWC.
Abstract: Dropwise condensation (DWC) heat transfer depends strongly on the maximum diameter (Dmax) of condensate droplets departing from the condenser surface. This study presents a facile technique implemented to gain control of Dmax in DWC within vapor/air atmospheres. We demonstrate how this approach can enhance the corresponding heat transfer rate by harnessing the capillary forces in the removal of the condensate from the surface. We examine various hydrophilic-superhydrophilic patterns, which, respectively, sustain and combine DWC and filmwise condensation on the substrate. The material system uses laser-patterned masking and chemical etching to achieve the desired wettability contrast and does not employ any hydrophobizing agent. By applying alternating straight parallel strips of hydrophilic (contact angle ∼78°) mirror-finish aluminum and superhydrophilic regions (etched aluminum) on the condensing surface, we show that the average maximum droplet size on the less-wettable domains is nearly 42% of the width of the corresponding strips. An overall improvement in the condensate collection rate, up to 19% (as compared to the control case of DWC on mirror-finish aluminum) was achieved by using an interdigitated superhydrophilic track pattern (on the mirror-finish hydrophilic surface) inspired by the vein network of plant leaves. The bioinspired interdigitated pattern is found to outperform the straight hydrophilic-superhydrophilic pattern design, particularly under higher humidity conditions in the presence of noncondensable gases (NCG), a condition that is more challenging for maintaining sustained DWC.
TL;DR: In this paper, a solution-phase nanocapsule method for active and durable electrocatalytic oxygen evolution reaction (OER) catalysts in alkaline electrolyte was proposed.
Abstract: The electrocatalytic oxygen evolution reaction (OER) is a critical anode reaction often coupled with electron or photoelectron CO2 reduction and H2 evolution reactions at the cathode for renewable energy conversion and storage. However, the sluggish OER kinetics and the utilization of precious metal catalysts are key obstacles in the broad deployment of these energy technologies. Herein, inexpensive supported 4 nm Ni–Fe nanoparticles (NiyFe1–yOx/C) featuring amorphous structures have been prepared via a solution-phase nanocapsule method for active and durable OER electrocatalysts in alkaline electrolyte. The Ni–Fe nanoparticle catalyst containing 31% Fe (Ni0.69Fe0.31Ox/C) shows the highest activity, exhibiting a 280 mV overpotential at 10 mA cm–2 (equivalent to 10% efficiency of solar-to-fuel conversion) and a Tafel slope of 30 mV dec–1 in 1.0 M KOH solution. The achieved OER activity outperforms NiOx/C and commercial Ir/C catalysts and is close to the highest performance of crystalline Ni–Fe thin films r...
TL;DR: The validity of the t-plot method is discussed in the case of hierarchical porous materials exhibiting both micro- and mesoporosities, and an abacus is given to correct the underestimated microporous volume by the t -plot method.
Abstract: The t-plot method is a well-known technique which allows determining the micro- and/or mesoporous volumes and the specific surface area of a sample by comparison with a reference adsorption isotherm of a nonporous material having the same surface chemistry. In this paper, the validity of the t-plot method is discussed in the case of hierarchical porous materials exhibiting both micro- and mesoporosities. Different hierarchical zeolites with MCM-41 type ordered mesoporosity are prepared using pseudomorphic transformation. For comparison, we also consider simple mechanical mixtures of microporous and mesoporous materials. We first show an intrinsic failure of the t-plot method; this method does not describe the fact that, for a given surface chemistry and pressure, the thickness of the film adsorbed in micropores or small mesopores (< 10σ, σ being the diameter of the adsorbate) increases with decreasing the pore size (curvature effect). We further show that such an effect, which arises from the fact that the surface area and, hence, the free energy of the curved gas/liquid interface decreases with increasing the film thickness, is captured using the simple thermodynamical model by Derjaguin. The effect of such a drawback on the ability of the t-plot method to estimate the micro- and mesoporous volumes of hierarchical samples is then discussed, and an abacus is given to correct the underestimated microporous volume by the t-plot method.
TL;DR: The interactions of CO2 with indium metal electrodes have been characterized for electrochemical formate production and it was observed that formate is the major product at unprecedentedly low overpotentials at the anodized surface.
Abstract: The interactions of CO2 with indium metal electrodes have been characterized for electrochemical formate production. The electrode oxidation state, morphology, and voltammetric behaviors were systematically probed. It was found that an anodized indium electrode stabilized formate production over time compared to etched indium electrodes and indium electrodes bearing a native oxide in applied potential range of -1.4 to -1.8 V vs SCE. In addition, it was observed that formate is the major product at unprecedentedly low overpotentials at the anodized surface. A surface hydroxide species was observed suggesting a mechanism of formate production that involves insertion of CO2 at the indium interface to form an electroactive surface bicarbonate species.
TL;DR: This is the first report which demonstrates single-step, direct flame synthesis of N-doped turbostratic carbon NPs and their application as a potential anode material with high capacity and superior battery performance.
Abstract: Nitrogen-doped turbostratic carbon nanoparticles (NPs) are prepared using fast single-step flame synthesis by directly burning acetonitrile in air atmosphere and investigated as an anode material for lithium-ion batteries. The as-prepared N-doped carbon NPs show excellent Li-ion stoarage properties with initial discharge capacity of 596 mA h g(-1), which is 17% more than that shown by the corresponding undoped carbon NPs synthesized by identical process with acetone as carbon precursor and also much higher than that of commercial graphite anode. Further analysis shows that the charge-discharge process of N-doped carbon is highly stable and reversible not only at high current density but also over 100 cycles, retaining 71% of initial discharge capacity. Electrochemical impedance spectroscopy also shows that N-doped carbon has better conductivity for charge and ions than that of undoped carbon. The high specific capacity and very stable cyclic performance are attributed to large number of turbostratic defects and N and associated increased O content in the flame-synthesized N-doped carbon. To the best of our knowledge, this is the first report which demonstrates single-step, direct flame synthesis of N-doped turbostratic carbon NPs and their application as a potential anode material with high capacity and superior battery performance. The method is extremely simple, low cost, energy efficient, very effective, and can be easily scaled up for large scale production.
TL;DR: A study based on operando electrochemical scanning tunneling microscopy has shown that a polycrystalline Cu electrode held at a fixed negative potential, -0.9 V (vs SHE), in the vicinity of CO2 reduction reactions (CO2RR) in 0.1 M KOH, undergoes stepwise surface reconstruction.
Abstract: A study based on operando electrochemical scanning tunneling microscopy (EC-STM) has shown that a polycrystalline Cu electrode held at a fixed negative potential, −0.9 V (vs SHE), in the vicinity of CO2 reduction reactions (CO2RR) in 0.1 M KOH, undergoes stepwise surface reconstruction, first to Cu(111) within 30 min, and then to Cu(100) after another 30 min; no further surface transformations occurred after establishment of the Cu(100) surface. The results may help explain the Cu(100)-like behavior of Cu(pc) in terms of CO2RR product selectivity. They likewise suggest that products exclusive to Cu(100) single-crystal electrodes may be generated through the use of readily available inexpensive polycrystalline Cu electrodes. The study highlights the dynamic nature of heterogeneous electrocatalyst surfaces and also underscores the importance of operando interrogations when structure–composition–reactivity correlations are intended.
TL;DR: It is demonstrated that the surface characteristics of the PDA films can be readily tuned by controlling the competitive interplay between PDA aggregation in solution and deposition on the substrate.
Abstract: Surface-adherent polydopamine (PDA) films as multifunctional coatings can be easily deposited onto a wide range of materials through dopamine self-polymerization. However, a lack of in-depth understanding of PDA aggregation and deposition processes and definite structure elucidation of PDA make it challenging to tailor the surface characteristic and functionality of the PDA films. Herein, we demonstrate that the surface characteristics of the PDA films can be readily tuned by controlling the competitive interplay between PDA aggregation in solution and deposition on the substrate. Moreover, a structural investigation of the PDA films using analytical tools such as X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) allows us to propose a new structure model for the PDA building block. The (DHI)2/PCA trimer complex, which consists of two 5,6-dihydroxyindole (DHI) units and one pyrrole...
TL;DR: Nanocellulose-based Pickering emulsions can be designed with a substantial degree of control, as demonstrated by the stability of the chemically tailored NFC double emulsion, and it was demonstrated that increased nanofiber length leads to increased stability.
Abstract: Nanocelluloses are bio-based nanoparticles of interest as stabilizers for oil-in-water (o/w) Pickering emulsions. In this work, the surface chemistry of nanocelluloses of different length, nanofibrillated cellulose (NFC, long) and cellulose nanocrystals (CNC, short), was successfully tailored by chemical modification with lauroyl chloride (C12). The resulting nanofibers were less hydrophilic than the original and able to stabilize water-in-oil (w/o) emulsions. The combination of the two types of nanocelluloses (C12-modified and native) led to new surfactant-free oil-in-water-in-oil (o/w/o) double emulsions stabilized by nanocellulose at both interfaces. Characterization was performed with respect to droplet size distribution, droplet stability over time, and stability after centrifugation. Nanocellulose-based Pickering emulsions can be designed with a substantial degree of control, as demonstrated by the stability of the chemically tailored NFC double emulsions. Furthermore, it was demonstrated that increased nanofiber length leads to increased stability.
TL;DR: The graphite-like nanostructure observed in the carbonized polydopamine nanoparticles in nitrogen (or argon) environment at 800 °C provides clear evidence for a layered-stacking supramolecular structure of polydipamine.
Abstract: Polydopamine is not only a multifunctional biopolymer with promising optoelectronic properties but it is also a versatile coating platform for different surfaces. The structure and formation of polydopamine is an active area of research. Some studies have supposed that polydopamine is composed of covalently bonded dihydroxyindole, indoledione, and dopamine units, but others proposed that noncovalent self-assembly contributes to polydopamine formation as well. However, it is difficult to directly find the details of supramolecular structure of polydopamine via self-assembly. In this study, we first report the graphite-like nanostructure observed in the carbonized polydopamine nanoparticles in nitrogen (or argon) environment at 800 °C. Raman characterization, which presents the typical D band and G band, confirmed the existence of graphite-like nanostructures. Our observation provides clear evidence for a layered-stacking supramolecular structure of polydopamine. Particularly, the size of graphite-like doma...
TL;DR: The ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf2N]) offers new ways to modulate the electrochemical reduction of carbon dioxide by promoting the formation of carbon monoxide instead of oxalate anion.
Abstract: The ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf2N]) offers new ways to modulate the electrochemical reduction of carbon dioxide. [emim][Tf2N], when present as the supporting electrolyte in acetonitrile, decreases the reduction overpotential at a Pb electrode by 0.18 V as compared to tetraethylammonium perchlorate as the supporting electrolyte. More interestingly, the ionic liquid shifts the reaction course during the electrochemical reduction of carbon dioxide by promoting the formation of carbon monoxide instead of oxalate anion. With increasing concentration of [emim][Tf2N], a carboxylate species with reduced CO2 covalently bonded to the imidazolium ring is formed along with carbon monoxide. The results highlight the catalytic effects of the medium in modulating the CO2 reduction products.
TL;DR: Tris buffer is disclosed as an efficient modulator of polydopamine buildup and properties for the rational control and fine-tuning of melanin aggregate size, morphology, and free radical behavior.
Abstract: Despite the growing technological interest of polydopamine (dopamine melanin)-based coatings for a broad variety of applications, the factors governing particle size, shape, and electronic properties of this bioinspired multifunctional material have remained little understood. Herein, we report a detailed characterization of polydopamine growth, particle morphology, and paramagnetic properties as a function of dopamine concentration and nature of the buffer (pH 8.5). Dynamic Light Scattering data revealed an increase in the hydrodynamic radii (Rh) of melanin particles with increasing dopamine concentration in all buffers examined, especially in phosphate buffer. Conversely, a marked inhibition of particle growth was apparent in Tris buffer, with Rh remaining as low as <100 nm during polymerization of 0.5 mM dopamine. Small angle neutron scattering data suggested formation of bidimensional structures in phosphate or bicarbonate buffers, while apparently three-dimensional fractal objects prevailed in Tris b...
TL;DR: The current state of the art in the microfluidic-based synthesis of monodisperse functional microparticles is described, which indicates that these functionalized particles have significant potential for practical applications as a new class of colloidal materials.
Abstract: Isotropic microparticles prepared from a suspension that undergoes polymerization have long been used for a variety of applications. Bulk emulsification procedures produce polydisperse emulsion droplets that are transformed into spherical microparticles through chemical or physical consolidation. Recent advances in droplet microfluidics have enabled the production of monodisperse emulsions that yield highly uniform microparticles, albeit only on a drop-by-drop basis. In addition, microfluidic devices have provided a variety of means for particle functionalization through shaping, compartmentalizing, and microstructuring. These functionalized particles have significant potential for practical applications as a new class of colloidal materials. This feature article describes the current state of the art in the microfluidic-based synthesis of monodisperse functional microparticles. The three main sections of this feature article discuss the formation of isotropic microparticles, engineered microparticles, an...
TL;DR: It is demonstrated that, dependent on dynamics of formation and resulting morphology of the liquid metal-substrate interface, GaInSn adhesion can occur in two modes, and it is demonstrated how these two adhesion modes limit microcontact printing of GaIn Sn patterns but can be exploited to repeatedly print individual sub-200 nm liquid metal drops.
Abstract: Gallium-based liquid metals are of interest for a variety of applications including flexible electronics, soft robotics, and biomedical devices. Still, nano- to microscale device fabrication with these materials is challenging because, despite having surface tension 10 times higher than water, they strongly adhere to a majority of substrates. This unusually high adhesion is attributed to the formation of a thin oxide shell; however, its role in the adhesion process has not yet been established. In this work, we demonstrate that, dependent on dynamics of formation and resulting morphology of the liquid metal–substrate interface, GaInSn adhesion can occur in two modes. The first mode occurs when the oxide shell is not ruptured as it makes contact with the substrate. Because of the nanoscale topology of the oxide surface, this mode results in minimal adhesion between the liquid metal and most solids, regardless of substrate’s surface energy or texture. In the second mode, the formation of the GaInSn–substrat...
TL;DR: The wetting properties of graphene oxide are characterized by performing classical molecular dynamics simulations with relevant applications in graphene oxide-derived functional materials and offer a fundamental understanding of their wetting and flow phenomena.
Abstract: We characterize the wetting properties of graphene oxide by performing classical molecular dynamics simulations. With oxygen-containing functional groups on the basal plane, graphene becomes hydrophilic and the water contact angle decreases with their concentration, c. The concentration dependence displays a transition at c ≈ 11% as defined by the interacting range of hydrogen bonds with oxidized groups and water. Patterns of the oxidized region and the morphological corrugation of the sheet strongly influence the spreading of water droplets with their lateral spans defined by corresponding geometrical parameters and thus can be used to control their behavior on the surface. These results are discussed with respect to relevant applications in graphene oxide-derived functional materials and offer a fundamental understanding of their wetting and flow phenomena.
TL;DR: The synthesis of reduced graphene oxide (RGO) sheet wrapped polyaniline (PANI) nanowire arrays grown on nitrogen-doped carbon fiber cloth (eCFC) shows an enhanced capacitive behavior and exhibits excellent charge/discharge rates and a good cycling stability.
Abstract: We report the synthesis of reduced graphene oxide (RGO) sheet wrapped polyaniline (PANI) nanowire arrays grown on nitrogen-doped carbon fiber cloth (eCFC). The RGO coating layer is important to accommodate volume change and mechanical deformation of the coated PANI nanowires arrays during the long-term charge/discharge processes. The resulting hierarchical symmetric supercapacitor based on RGO/PANI/eCFC composites shows an enhanced capacitive behavior with a maximum energy density of 25.4 Wh kg(-1), a maximum power density of 92.2 kW kg(-1) and a specific capacitance of 1145 F g(-1), which is higher than that of PANI/eCFC (1050 F g(-1)) and GO/PANI/eCFC (940 F g(-1)). Moreover, the assembled supercapacitor exhibits excellent charge/discharge rates and a good cycling stability, retaining over 94% of its initial capacitance after 5000 cycles.
TL;DR: The new role of GR does contribute to the overall photoactivity enhancement of BGR-WO3 NR nanocomposites and the synergistic contribution of GR on improving the photoactivity of WO3NRs and the underlying reaction mechanism have been analyzed by the structure-photoactivity correlation analysis and controlled experiments using radicals scavengers.
Abstract: The new role of graphene (GR) in boosting the two-electron reduction of O2 to H2O2 has been first identified in the GR–WO3 nanorod (NR) nanocomposite photocatalysts, which are fabricated by a facile, solid electrostatic self-assembly strategy to integrate the positively charged branched poly(ethylenimine) (BPEI)-GR (BGR) and negatively charged WO3 NRs at room temperature. Photoactivity test shows that, as compared to WO3 NRs, BGR–WO3 NRs with an appropriate addition ratio of GR exhibit remarkably enhanced and stable visible-light photoactivity toward the degradation of Rhodamine B. Besides the common roles of GR observed in the GR-based composite photocatalysts in the literature, including enhancing the visible-light absorption intensity, improving the lifetime and transfer of photogenerated charge carriers, and increasing the adsorption capacity for reactants, we have observed the new role of GR in boosting the two-electron reduction of O2 to H2O2 in this specific BGR–WO3 NR photocatalyst system. Importa...
TL;DR: It is shown that patterned retarders can be made by a two-step polymerization process which is successfully employed in a transflective display principle.
Abstract: Monolithically ordered liquid crystal polymer networks are formed by the photoinitiated polymerization of multifunctional liquid crystal monomers. This paper describes the relevant principles and methods, the basic structure-property relationships in terms of mesogenic properties of the monomers, and the mechanical and optical properties of the polymers. Strategies are discussed to control the molecular orientation by various means and in all three dimensions. The versatility of the process is demonstrated by two examples of films with a patterned molecular order. It is shown that patterned retarders can be made by a two-step polymerization process which is successfully employed in a transflective display principle. A transflective display is a liquid crystal display that operates in both a reflective mode using ambient light and a transmissive mode with light coming from a backlight system. Furthermore, a method is discussed to create a patterned film in a single polymerization process. This film has alternating planar chiral nematic areas next to perpendicularly oriented (so-called homeotropic) areas. When applied as a coating to a substrate, the film changes its surface texture. During exposure to UV light, it switches from a flat to a corrugated state.
TL;DR: The present result suggests that the morphology-dependent photoreduction of Cr(VI) by SnS2 nanomaterial under visible light exposure will endorse a new technique for harvesting energy and purification of wastewater.
Abstract: A mild, template free protocol has been demonstrated for SnS2 nanoflake formation at the gram level from SnCl2 and thioacetamide (TAA). The SnS2 nanoflakes congregate to nanoflowers and nanoyarns with variable TAA concentrations. BET measurements reveal that the synthesized nanomaterials are highly porous having very high surface area, and the nanoflower has higher surface area than the nanoyarn. The synthesized nanomaterial finds application for promoting photoreduction of extremely toxic and lethal Cr(VI) under visible light irradiation due to their porous nature. The nanoflowers photocatalyst is proved to be superior to nanoyarn due to the increased surface area and higher pore volume. It was also inferred that increased pH decreased the reaction rate. The present result suggests that the morphology-dependent photoreduction of Cr(VI) by SnS2 nanomaterial under visible light exposure will endorse a new technique for harvesting energy and purification of wastewater.
TL;DR: It was found that all the topographies investigated provoke a significant reduction in bacterial adhesion relative to the smooth control samples regardless of surface hydrophobicity/hydrophilicity.
Abstract: The influence of surface topography on bacterial adhesion has been investigated using a range of spatially organized microtopographic surface patterns generated on polydimethylsiloxane (PDMS) and three unrelated bacterial strains. The results presented indicate that bacterial cells actively choose their position to settle, differentiating upper and lower areas in all the surface patterns evaluated. Such selective adhesion depends on the cells’ size and shape relative to the dimensions of the surface topographical features and surface hydrophobicity/hydrophilicity. Moreover, it was found that all the topographies investigated provoke a significant reduction in bacterial adhesion (30–45%) relative to the smooth control samples regardless of surface hydrophobicity/hydrophilicity. This remarkable finding constitutes a general phenomenon, occurring in both Gram-positive and Gram-negative cells with spherical or rod shape, dictated by only surface topography. Collectively, the results presented in this study de...
TL;DR: It is demonstrated that the most essential freezing delay is characteristic of the superhydrophobic coating on aluminum, with the texture resistant to contact with ice and water, which can reach many hours at T = -8 °C and a few minutes at -23 °C.
Abstract: An increasing number of studies directed at supercooling water droplets on surfaces with different wettabilities have appeared in recent years. This activity has been stimulated by the recognition that water supercooling phenomena can be effectively used to develop methods for protecting outdoor equipment and infrastructure elements against icing and snow accretion. In this article, we discuss the nucleation kinetics of supercooled sessile water droplets on hydrophilic, hydrophobic, and superhydrophobic surfaces under isothermal conditions at temperatures of −8, −10, and −15 °C and a saturated water vapor atmosphere. The statistics of nucleation events for the ensembles of freezing sessile droplets is completed by the detailed analysis of the contact angle temperature dependence and freezing of individual droplets in a saturated vapor atmosphere. We have demonstrated that the most essential freezing delay is characteristic of the superhydrophobic coating on aluminum, with the texture resistant to contact ...