Showing papers in "Langmuir in 2015"
TL;DR: It is conclusively proved that reactive oxygen species (ROS) such as (•)OH, ( •)O2(-), and H2O2 are significantly produced from aqueous suspension of ZnO even in thedark and are mainly responsible for the activity in the dark up to 17%, rather than Zn(2+) ion leaching as proposed earlier.
Abstract: A systematic and complete antibacterial study on well-designed and well-characterized microparticle (micro), nanoparticle (nano), and capped nano ZnO has been carried out in both dark and light conditions with the objective of arriving at the mechanism of the antibacterial activity of ZnO, particularly in the dark. The present systematic study has conclusively proved that reactive oxygen species (ROS) such as •OH, •O2–, and H2O2 are significantly produced from aqueous suspension of ZnO even in the dark and are mainly responsible for the activity in the dark up to 17%, rather than Zn2+ ion leaching as proposed earlier. This work further confirms that surface defects play a major role in the production of ROS both in the presence and absence of light. In the dark, superoxide (•O2–) radical mediated ROS generation through singly ionized oxygen vacancy is proposed for the first time, and it is confirmed by EPR and scavenger studies. ROS such as •O2–, H2O2, and •OH have been estimated by UV–visible spectroscop...
472 citations
TL;DR: This historical review of dynamic light scattering discusses the basic principle, data analysis, and important precautions to be taken while analyzing colloids using DLS in a manner that can be understood by a beginner.
Abstract: Dynamic light scattering (DLS) has evolved as a fast, convenient tool for particle size analysis of noninteracting spherical colloids In this historical review, we discuss the basic principle, data analysis, and important precautions to be taken while analyzing colloids using DLS The effect of particle interaction, polydispersity, anisotropy, light absorption, and so forth, on measured diffusion coefficient is discussed New developments in this area such as diffusing wave spectroscopy, particle tracking analysis, microrheological studies using DLS, and so forth, are discussed in a manner that can be understood by a beginner
415 citations
TL;DR: This work presents a hitherto unexplored algal platform featuring Chlorella pyrenoidosa, which offers a high degree of consistency in morphology of synthesized silver nanoparticles and demonstrates the antibacterial and photocatalytic properties of these nanoparticles.
Abstract: Biogenic synthesis of metal nanoparticles is of considerable interest, as it affords clean, biocompatible, nontoxic, and cost-effective fabrication. Driven by their ability to withstand variable extremes of environmental conditions, several microorganisms, notably bacteria and fungi, have been investigated in the never-ending search for optimal nanomaterial production platforms. Here, we present a hitherto unexplored algal platform featuring Chlorella pyrenoidosa, which offers a high degree of consistency in morphology of synthesized silver nanoparticles. Using a suite of characterization methods, we reveal the intrinsic crystallinity of the algae-derived nanoparticles and the functional moieties associated with its surface stabilization. Significantly, we demonstrate the antibacterial and photocatalytic properties of these silver nanoparticles and discuss the potential mechanisms that drive these critical processes. The blend of photocatalytic and antibacterial properties coupled with their intrinsic biocompatibility and eco-friendliness make these nanoparticles particularly attractive for wastewater treatment.
411 citations
TL;DR: Key aspects and findings related to the physics of ice formation on surfaces are discussed and how such knowledge could be employed to rationally develop surfaces with extreme resistance to icing (extraordinary icephobicity).
Abstract: Icing of surfaces is commonplace in nature and technology, affecting everyday life and sometimes causing catastrophic events. Understanding (and counteracting) surface icing brings with it significant scientific challenges that requires interdisciplinary knowledge from diverse scientific fields such as nucleation thermodynamics and heat transfer, fluid dynamics, surface chemistry, and surface nanoengineering. Here we discuss key aspects and findings related to the physics of ice formation on surfaces and show how such knowledge could be employed to rationally develop surfaces with extreme resistance to icing (extraordinary icephobicity). Although superhydrophobic surfaces with micro-, nano-, or (often biomimetic) hierarchical roughnesses have shown in laboratory settings (under certain conditions) excellent repellency and low adhesion to water down to temperatures near or below the freezing point, extreme icephobicity necessitates additional important functionalities. Other approaches, such as lubricant-impregnated surfaces, exhibit both advantages and serious limitations with respect to icing. In all, a clear path toward passive surfaces with extreme resistance to ice formation remains a challenge, but it is one well worth undertaking. Equally important to potential applications is scalable surface manufacturing and the ability of icephobic surfaces to perform reliably and sustainably outside the laboratory under adverse conditions. Surfaces should possess mechanical and chemical stability, and they should be thermally resilient. Such issues and related research directions are also addressed in this article.
267 citations
TL;DR: The merits and drawbacks of regeneration schemes that have been proven in various biosensor systems are discussed and parameters for successful regeneration are indicated based on a systematic review of the literature.
Abstract: Biosensors are ideally portable, low-cost tools for the rapid detection of pathogens, proteins, and other analytes. The global biosensor market is currently worth over 10 billion dollars annually and is a burgeoning field of interdisciplinary research that is hailed as a potential revolution in consumer, healthcare, and industrial testing. A key barrier to the widespread adoption of biosensors, however, is their cost. Although many systems have been validated in the laboratory setting and biosensors for a range of analytes are proven at the concept level, many have yet to make a strong commercial case for their acceptance. Though it is true with the development of cheaper electrodes, circuits, and components that there is a downward pressure on costs, there is also an emerging trend toward the development of multianalyte biosensors that is pushing in the other direction. One way to reduce the cost that is suitable for certain systems is to enable their reuse, thus reducing the cost per test. Regenerating biosensors is a technique that can often be used in conjunction with existing systems in order to reduce costs and accelerate the commercialization process. This article discusses the merits and drawbacks of regeneration schemes that have been proven in various biosensor systems and indicates parameters for successful regeneration based on a systematic review of the literature. It also outlines some of the difficulties encountered when considering the role of regeneration at the point of use. A brief meta-analysis has been included in this review to develop a working definition for biosensor regeneration, and using this analysis only ∼60% of the reported studies analyzed were deemed a success. This highlights the variation within the field and the need to normalize regeneration as a standard process across the field by establishing a consensus term.
257 citations
TL;DR: It is shown that without the charge screening effect of divalent cations, the LPS is forced to overcome the thermodynamically unfavorable energy barrier and flip across the hydrophobic bilayer to minimize the repulsive electrostatic forces, resulting in about 20% mixing of LPS and DPPC between the inner and outer bilayer leaflets.
Abstract: The Gram-negative bacterial outer membrane (GNB-OM) is asymmetric in its lipid composition with a phospholipid-rich inner leaflet and an outer leaflet predominantly composed of lipopolysaccharides (LPS). LPS are polyanionic molecules, with numerous phosphate groups present in the lipid A and core oligosaccharide regions. The repulsive forces due to accumulation of the negative charges are screened and bridged by the divalent cations (Mg2+ and Ca2+) that are known to be crucial for the integrity of the bacterial OM. Indeed, chelation of divalent cations is a well-established method to permeabilize Gram-negative bacteria such as Escherichia coli. Here, we use X-ray and neutron reflectivity (XRR and NR, respectively) techniques to examine the role of calcium ions in the stability of a model GNB-OM. Using XRR we show that Ca2+ binds to the core region of the rough mutant LPS (RaLPS) films, producing more ordered structures in comparison to divalent cation free monolayers. Using recently developed solid-suppor...
248 citations
TL;DR: An innovative approach to create a new modified textile by direct in situ growth of vertically aligned one-dimensional ZnO NRs onto textile surfaces, which can serve with potential for biosensing, photocatalysis, and antibacterial applications.
Abstract: Recently, one-dimensional nanostructures with different morphologies (such as nanowires, nanorods (NRs), and nanotubes) have become the focus of intensive research, because of their unique properties with potential applications. Among them, zinc oxide (ZnO) nanomaterials has been found to be highly attractive, because of the remarkable potential for applications in many different areas such as solar cells, sensors, piezoelectric devices, photodiode devices, sun screens, antireflection coatings, and photocatalysis. Here, we present an innovative approach to create a new modified textile by direct in situ growth of vertically aligned one-dimensional (1D) ZnO NRs onto textile surfaces, which can serve with potential for biosensing, photocatalysis, and antibacterial applications. ZnO NRs were grown by using a simple aqueous chemical growth method. Results from analyses such as X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed that the ZnO NRs were dispersed over the entire surface of the...
207 citations
TL;DR: A novel copper mesh film is reported, which is superhydrophobic and superHydrophilic for nonalkaline water and alkaline water, respectively, and has such a special ability that allows it to be used in other applications, such as sewage purification, filtration, and microfluidic device.
Abstract: Recently, materials with controlled oil/water separation ability became a new research focus. Herein, we report a novel copper mesh film, which is superhydrophobic and superhydrophilic for nonalkaline water and alkaline water, respectively. Meanwhile, the film shows superoleophobicity in alkaline water. Using the film as a separating membrane, the oil/water separating process can be triggered on-demand by changing the water pH, which shows a good controllability. Moreover, it is found that the nanostructure and the appropriate pore size of the substrate are important for realization of a good separation effect. This paper offers a new insight into the application of surfaces with switchable wettability, and the film reported here has such a special ability that allows it to be used in other applications, such as sewage purification, filtration, and microfluidic device.
201 citations
TL;DR: It is shown that the surfactant-mediated interactions between particles and the liquid-gas and liquid-solid interfaces, rather than the flow patterns, primarily define the morphology of the dry deposit in a robust and reproducible manner.
Abstract: We study the effect of surfactants on the deposits formed after the evaporation of colloidal suspension drops, at initial concentrations lower than the critical micellar concentrations, for various particle/surfactant mixtures. We show that the surfactant-mediated interactions between particles and the liquid–gas (LG) and liquid–solid (LS) interfaces, rather than the flow patterns, primarily define the morphology of the dry deposit in a robust and reproducible manner. For like-charged particle/surfactant mixtures, most of the particles form a ring-shaped deposit (according to the so-called “Coffee-Ring Effect”), but some particles can also be deposited inside the ring in a way that is modulated by electrostatic interactions between the particles and the LS interface. For oppositely charged systems, surfactant adsorption to the particle surface strongly affects particle-LG interface interactions, which in turn control the deposition pattern. For low surfactant concentrations, coffee-rings are systematicall...
184 citations
TL;DR: In this article, direct force measurements on a broad class of hydrophobic and hydrophilic surfaces have enabled the development of a general interaction potential per unit area, W(D) = −2γiHy exp(−D/DH).
Abstract: We review direct force measurements on a broad class of hydrophobic and hydrophilic surfaces. These measurements have enabled the development of a general interaction potential per unit area, W(D) = −2γiHy exp(−D/DH) in terms of a nondimensional Hydra parameter, Hy, that applies to both hydrophobic and hydrophilic interactions between extended surfaces. This potential allows one to quantitatively account for additional attractions and repulsions not included in the well-known combination of electrostatic double layer and van der Waals theories, the so-called Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. The interaction energy is exponentially decaying with decay length DH ≈ 0.3–2 nm for both hydrophobic and hydrophilic interactions, with the exact value of DH depending on the precise system and conditions. The pre-exponential factor depends on the interfacial tension, γi, of the interacting surfaces and Hy. For Hy > 0, the interaction potential describes interactions between partially hydrophobic surfac...
178 citations
TL;DR: A general approach to imparting both the shape memory and self-healing properties to chemically cross-linked hydrogels that otherwise do not have such functionalities is demonstrated.
Abstract: A double-network polymer hydrogel composed of chemically cross-linked poly(ethylene glycol) (PEG) and physically cross-linked poly(vinyl alcohol) (PVA) was prepared. When the hydrogel (70 wt % of water) is subjected to freezing/thawing treatment under strain, the enhanced physical network as a result of crystallization of PVA chains can stabilize the hydrogel deformation after removal of the external force at room temperature. Subsequent disruption of the physical network of PVA by heating allows for the recovery of the initial shape of the hydrogel. Moreover, the double-network hydrogel exhibits self-healing capability stemming from the physical network of PVA by virtue of the extensive interchain hydrogen bonding between the hydroxyl side groups. This study thus demonstrates a general approach to imparting both the shape memory and self-healing properties to chemically cross-linked hydrogels that otherwise do not have such functionalities. Moreover, by making use of the fixed hydrogel elongation, the ef...
TL;DR: The Tafel slope on the amorphous film suggests the Volmer-Heyrovsky mechanism as a major pathway for the HER in which a primary discharging step for hydrogen adsorption is followed by the rate-determining electrochemical desorption of hydrogen gas.
Abstract: Recently amorphous MoS2 thin film has attracted great attention as an emerging material for electrochemical hydrogen evolution reaction (HER) catalyst. Here we prepare the amorphous MoS2 catalyst on Au by atomic layer deposition (ALD) using molybdenum hexacarbonyl (Mo(CO)6) and dimethyl disulfide (CH3S2CH3) as Mo and S precursors, respectively. Each active site of the amorphous MoS2 film effectively catalyzes the HER with an excellent turnover frequency of 3 H2/s at 0.215 V versus the reversible hydrogen electrode (RHE). The Tafel slope (47 mV/dec) on the amorphous film suggests the Volmer–Heyrovsky mechanism as a major pathway for the HER in which a primary discharging step (Volmer reaction) for hydrogen adsorption is followed by the rate-determining electrochemical desorption of hydrogen gas (Heyrovsky reaction). In addition, the amorphous MoS2 thin film is electrically evaluated to be rather conductive (0.22 Ω–1 cm–1 at room temperature) with a low activation energy of 0.027 eV. It is one of origins fo...
TL;DR: This study provides valuable insights into the effects of the PEA doping ratios on photoluminescence efficiency, biocompatibility, cellular uptake, and optical bioimaging of CDs.
Abstract: Photoluminescent carbon dots (CDs) have received ever-increasing attention in the application of optical bioimaging because of their low toxicity, tunable fluorescent properties, and ultracompact size. We report for the first time on enhanced photoluminescence (PL) performance influenced by structure effects among the various types of nitrogen doped (N-doped) PL CDs. These CDs were facilely synthesized from condensation carbonization of linear polyethylenic amine (PEA) analogues and citric acid (CA) of different ratios. Detailed structural and property studies demonstrated that either the structures or the molar ratio of PEAs altered the PL properties of the CDs. The content of conjugated π-domains with C═N in the carbon backbone was correlated with their PL Quantum Yield (QY) (up to 69%). The hybridization between the surface/molecule state and the carbon backbone synergistically affected the chemical/physical properties. Also, long-chain polyethylenic amine (PEA) molecule-doped CDs exhibit increasing ph...
TL;DR: Using the MoS2 nanosheets to coat the surface of Bi2S3 discoids composites boosts the light-harvesting efficiency and charge separation and promotes faster charge transport and collection, thus leading to the higher activity of the photocatalytic reduction of Cr(VI) under visible light irradiation.
Abstract: Myriad materials with desirable functional property resulting from their unique structures ignite enormous interest in synthesizing materials with controlled structural morphology toward achieving novel or enhanced properties for target applications. Herein, the novel and unique two-dimensional (2D) MoS2 nanosheet-coated Bi2S3 discoids composites, which feature a Bi2S3-core/MoS2-shell structure, have been elaborated via a facile anion-exchange strategy. Using the MoS2 nanosheets to coat the surface of Bi2S3 discoids boosts the light-harvesting efficiency and charge separation and promotes faster charge transport and collection, thus leading to the higher activity of the photocatalytic reduction of Cr(VI) under visible light irradiation (λ > 400 nm). In particular, the phase evolution and possible formation mechanism of the MoS2–Bi2S3 core–shell structure have been explored by virtue of temperature- and time-dependent experiments. It is anticipated that this work could promote further interest in adopting ...
TL;DR: Comparison between experimental CCCs and those calculated by the theory of Derjaguin, Landau, Verwey, and Owerbeek reveals that variations in the surface charge due to ionic adsorption are mainly responsible for the ion specific effects in the aggregation process.
Abstract: Ion specific effects of monovalent salts on charging and aggregation for two types of polystyrene latex particles were investigated by electrophoresis and time-resolved light scattering. The chemical composition of the electrolytes was systematically varied in the experiments. Accordingly, NaH2PO4, NaF, NaCl, NaBr, NaNO3, and NaSCN were used to vary the anions and N(CH3)4Cl, NH4Cl, CsCl, KCl, NaCl, and LiCl for the cations. The salt concentration dependence of the electrophoretic mobilities indicates that the surface charge was screened by the counterions when their concentrations increased. For the SCN– ions, adsorption on positively charged particles leads to charge reversal. The aggregation rates are small at low electrolyte concentrations indicating stable dispersions under these conditions, and they increase with the salt concentration. When viscosity corrections are taken into account, no ion specific effects in the fast aggregation regime can be established. The slow and fast aggregation regimes ar...
TL;DR: The electrochemical corrosion test results indicated that the superhydrophobic coatings possessed excellent corrosion resistance, which could supply efficient and long-term preservation for the bare Al substrate.
Abstract: A simple method was used to generate colorful hydrophobic stearate particles via chemical reactions between inorganic salts and sodium stearate. Colored self-cleaning superhydrophobic coatings were prepared through a facile one-step spray-coating process by spraying the stearate particle suspensions onto stainless steel substrates. Furthermore, the colorful superhydrophobic coating maintains excellent chemical stability under both harsh acidic and alkaline circumstances. After being immersed in a 3.5 wt % NaCl aqueous solution for 1 month, the as-prepared coatings remained superhydrophobic; however, they lost their self-cleaning property with a sliding angle of about 46 ± 3°. The corrosion behavior of the superhydrophobic coatings on the Al substrate was characterized by the polarization curve and electrochemical impedance spectroscopy (EIS). The electrochemical corrosion test results indicated that the superhydrophobic coatings possessed excellent corrosion resistance, which could supply efficient and lo...
TL;DR: The dependence of the twisting on the volume fraction was related to the increase in the magnitude of the repulsive interactions between the charged rods as the average separation distance decreases.
Abstract: The packing of cellulose nanocrystals (CNC) in the anisotropic chiral nematic phase has been investigated over a wide concentration range by small-angle X-ray scattering (SAXS) and laser diffraction. The average separation distance between the CNCs and the average pitch of the chiral nematic phase have been determined over the entire isotropic-anisotropic biphasic region. The average separation distances range from 51 nm, at the onset of the anisotropic phase formation, to 25 nm above 6 vol % (fully liquid crystalline phase) whereas the average pitch varies from ≈15 μm down to ≈2 μm as ϕ increases from 2.5 up to 6.5 vol %. Using the cholesteric order, we determine that the twist angle between neighboring CNCs increases from about 1° up to 4° as ϕ increases from 2.5 up to 6.5 vol %. The dependence of the twisting on the volume fraction was related to the increase in the magnitude of the repulsive interactions between the charged rods as the average separation distance decreases.
TL;DR: It is reported that water contact angle (WCA) of freshly exfoliated MoS2 shows temporal evolution with an intrinsic WCA of 69.0 ± 3.8° that increases to 89.1° after 1 day exposure to ambient air.
Abstract: 2D semiconductors allow for unique and ultrasensitive devices to be fabricated for applications ranging from clinical diagnosis instruments to low-energy light-emitting diodes (LEDs). Graphene has championed research in this field since it was first fabricated; however, its zero bandgap creates many challenges. Transition metal dichalcogenides (TMDCs), e.g., MoS2, have a direct bandgap which alleviates the challenge of creating a bandgap in graphene-based devices. Water wettability of MoS2 is critical to device fabrication/performance and MoS2 has been believed to be hydrophobic. Herein, we report that water contact angle (WCA) of freshly exfoliated MoS2 shows temporal evolution with an intrinsic WCA of 69.0 ± 3.8° that increases to 89.0 ± 3.1° after 1 day exposure to ambient air. ATR-FTIR and ellipsometry show that the fresh, intrinsically mildly hydrophilic MoS2 surface adsorbs hydrocarbons from ambient air and thus becomes hydrophobic.
TL;DR: Theoretical study is presented on the wetting behaviors of water droplets over a lotus leaf to clarify the trade-offs among the potential energy change, the local pinning energy, and the adhesion energy.
Abstract: Theoretical study is presented on the wetting behaviors of water droplets over a lotus leaf. Experimental results are interpreted to clarify the trade-offs among the potential energy change, the local pinning energy, and the adhesion energy. The theoretical parameters, calculated from the experimental results, are used to qualitatively explain the relations among surface fractal dimension, surface morphology, and dynamic wetting behaviors. The surface of a lotus leaf, which shows the superhydrophobic lotus effect, was dipped in ethanol to remove the plant waxes. As a result, the lotus effect is lost. The contact angle of a water drop decreased dramatically from 161° of the original surface to 122°. The water droplet was pinned on the surface. From the fractal analysis, the fractal region of the original surface was divided into two regions: a smaller-sized roughness region of 0.3–1.7 μm with D of 1.48 and a region of 1.7–19 μm with D of 1.36. By dipping the leaf in ethanol, the former fractal region, char...
TL;DR: Dilution of the rod gel led to disentanglement of the network of fractal aggregates with a subsequent macroscopic sedimentation of the suspensions, with a characteristic time that depends upon the ionic strength and surface charge density, revealing a threshold independent of salt content and the metastable out-of-equilibrium character of CNC suspensions.
Abstract: Aggregation of rodlike colloidal particles is investigated here through the aggregation process by either increasing ionic strength or decreasing surface charge density of cellulose nanocrystals (CNCs). The form factor of the nanoparticles is characterized up to the Guinier plateau using small-angle neutron scattering (SANS) extended to very small scattering vector Q. Ionic strength, above the threshold of screening charges, brings aggregative conditions that induced fractal organizations for both charged and uncharged CNCs. These two structures display respective fractal dimensions of 2.1 for charged CNCs at high ionic strength and 2.3 for desulfated CNCs over more than a decade of the scattering vector Q, irrespective of salinity, revealing a denser structuration for neutral particles. This is discussed in the framework of aggregation of rodlike particles with an aspect ratio higher than 8. Furthermore, dilution of the rod gel led to disentanglement of the network of fractal aggregates with a subsequent...
TL;DR: Polydopamine generated via a hydrothermal method shows similar chemical features and radical scavenging activity with that generated in a basic environment.
Abstract: A weak alkaline condition (pH > 8) is a general requirement for oxidative self-polymerization of dopamine. Here, we first demonstrated the generation of polydopamine in an acidic environment via a hydrothermal method. The pH scope of self-polymerization of dopamine is extended to pH ∼ 1 in a hydrothermal process. Polydopamine generated via a hydrothermal method shows similar chemical features and radical scavenging activity with that generated in a basic environment.
TL;DR: The reversibility of the process was demonstrated by shearing the dried product in the presence of water to obtain reconstituted emulsions with rheological properties comparable to those of the fresh emulsion.
Abstract: Physical trapping of a hydrophobic liquid oil in a matrix of water-soluble biopolymers was achieved using a facile two-step process by first formulating a surfactant-free oil-in-water emulsion stabilized by biopolymers (a protein and a polysaccharide) followed by complete removal of the water phase (by either high- or low-temperature drying of the emulsion) resulting in structured solid systems containing a high concentration of liquid oil (above 97 wt %). The microstructure of these systems was revealed by confocal and cryo-scanning electron microscopy, and the effect of biopolymer concentrations on the consistency of emulsions as well as the dried product was evaluated using a combination of small-amplitude oscillatory shear rheometry and large deformation fracture studies. The oleogel prepared by shearing the dried product showed a high gel strength as well as a certain degree of thixotropic recovery even at high temperatures. Moreover, the reversibility of the process was demonstrated by shearing the ...
TL;DR: New zwitterionic surface-responsive materials with controllable antifouling and friction capabilities for multifunctional applications are synthesized and characterized via the surface-initiated atom transfer radical polymerization.
Abstract: Development of smart, multifunction materials is challenging but important for many fundamental and industrial applications. Here, we synthesized and characterized zwitterionic poly(3-(1-(4-vinylbenzyl)-1H-imidazol-3-ium-3-yl)propane-1-sulfonate) (polyVBIPS) brushes as ion-responsive smart surfaces via the surface-initiated atom transfer radical polymerization. PolyVBIPS brushes were carefully characterized for their surface morphologies, compositions, wettability, and film thicknesses by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), contact angle, and ellipsometer, respectively. Salt-responsive, switching properties of polyVBIPS brushes on surface hydration, friction, and antifouling properties were further examined and compared both in water and in salt solutions with different salt concentrations and counterion types. Collective data showed that polyVBIPS brushes exhibited reversible surface wettability switching between in water and saturated NaCl solution. PolyVBIPS brushes in water induced the larger protein absorption, higher surface friction, and lower surface hydration than those in salt solutions, exhibiting "anti-polyelectrolyte effect" salt responsive behaviors. At appropriate ionic conditions, polyVBIPs brushes were able to switch to superlow fouling surfaces (<0.3 ng/cm(2) protein adsorption) and superlow friction surfaces (u ∼ 10(-3)). The relationship between brush structure and its salt-responsive performance was also discussed. This work provides new zwitterionic surface-responsive materials with controllable antifouling and friction capabilities for multifunctional applications.
TL;DR: The reduced graphene oxide nanosheets (RGOS) possess better friction reduction than GOS by virtue of hydrophobic surface properties, and both RGOS and GOS have weak antiwear properties due to the destroyed graphitic structure.
Abstract: Friction and wear properties of graphene nanosheets prepared by different processes as solid lubricant on silicon dioxide have been comparatively studied via calibrated atomic force microscopy. The effects of normal load, humidity, and velocity on the friction were also investigated. All kinds of graphene nanosheets possess friction-reduction properties on the nanoscale. Mechanically exfoliated graphene nanosheets exhibit ultralubrication and zero wear under high pressure due to perfect graphitic structure and a hydrophobic surface. Defects in chemical vapor deposited graphene nanosheets decrease the antiwear and friction-reduction capability. The graphene oxide nanosheets (GOS) show the weakest friction-reduction properties on account of destroyed graphitic structure and a hydrophilic surface. The reduced graphene oxide nanosheets (RGOS) possess better friction reduction than GOS by virtue of hydrophobic surface properties. Both RGOS and GOS have weak antiwear properties due to the destroyed graphitic st...
TL;DR: Spectra in micellar solution of nonionic Triton X-100 revealed that nile red dye penetrates the hydrophilic, interfacial poly(oxyethylene) region of the micelles but cannot reach the hydphobic, innermost core.
Abstract: The solubilization behavior of nile red dye in aqueous surfactant and micellar solutions was studied by optical spectroscopic techniques, dynamic light scattering, and atomic force microscopy. Nile red exhibits considerable absorption in the submicellar concentration region. When dispersed in aqueous surfactant and/or micellar solution, nile red molecules tend to form nonemissive dimers and/or H-type aggregates through π-π stacking interactions. This phenomenon may limit the use of nile red in solubilization studies. In the presence of ionic SDS and CTAB micelles, the solubilization of nile red appears to take place primarily at the charged micellar surface within the interfacial region. Similarly, spectra in micellar solution of nonionic Triton X-100 revealed that nile red dye penetrates the hydrophilic, interfacial poly(oxyethylene) region of the micelles but cannot reach the hydrophobic, innermost core. Our results therefore suggest that nile red dye must be chosen carefully when probing (micellar) hydrophobic environments and (micro)domains.
TL;DR: It was found that the CdS/TiO2 nanofibers that were photodeposited for 4 h exhibited the highest catalytic activity, with a conversion of 22% and a selectivity of 99%, which were much higher than those of commercial CdCdS.
Abstract: CdS/TiO2 heterojunction nanofibers have been successfully synthesized through the photodeposition of CdS on 1D TiO2 nanofibers that were prepared via a facile electrospinning method. The as-synthesized samples showed high photocatalytic activities upon selectively oxidizing a series of alcohols into corresponding aldehydes under visible light irradiation. TEM observations revealed that CdS was closely grown on the TiO2 nanofibers. Moreover, it was found that the CdS/TiO2 nanofibers that were photodeposited for 4 h exhibited the highest catalytic activity, with a conversion of 22% and a selectivity of 99%, which were much higher than those of commercial CdS. In addition, we also discuss the photoabsorption performance and the reaction mechanism of the photocatalytic oxidation of alcohols.
TL;DR: This study investigates pattern formation during evaporation of water-based nanofluid sessile droplets placed on a smooth silicon surface at various temperatures using an infrared thermography technique and an optical interferometry technique.
Abstract: This study investigates pattern formation during evaporation of water-based nanofluid sessile droplets placed on a smooth silicon surface at various temperatures. An infrared thermography technique was employed to observe the temperature distribution along the air–liquid interface of evaporating droplets. In addition, an optical interferometry technique is used to quantify and characterize the deposited patterns. Depending on the substrate temperature, three distinctive deposition patterns are observed: a nearly uniform coverage pattern, a “dual-ring” pattern, and multiple rings corresponding to “stick–slip” pattern. At all substrate temperatures, the internal flow within the drop builds a ringlike cluster of the solute on the top region of drying droplets, which is found essential for the formation of the secondary ring deposition onto the substrate for the deposits with the “dual-ring” pattern. The size of the secondary ring is found to be dependent on the substrate temperature. For the deposits with th...
TL;DR: An exceptionally good control over theMoS2 coverage is maintained using an approach based on cycles of Mo evaporation and sulfurization to first nucleate the MoS2 nanoislands and then gradually increase their size.
Abstract: We present a method for synthesizing large area epitaxial single-layer MoS2 on the Au(111) surface in ultrahigh vacuum. Using scanning tunneling microscopy and low energy electron diffraction, the evolution of the growth is followed from nanoscale single-layer MoS2 islands to a continuous MoS2 layer. An exceptionally good control over the MoS2 coverage is maintained using an approach based on cycles of Mo evaporation and sulfurization to first nucleate the MoS2 nanoislands and then gradually increase their size. During this growth process the native herringbone reconstruction of Au(111) is lifted as shown by low energy electron diffraction measurements. Within the MoS2 islands, we identify domains rotated by 60° that lead to atomically sharp line defects at domain boundaries. As the MoS2 coverage approaches the limit of a complete single layer, the formation of bilayer MoS2 islands is initiated. Angle-resolved photoemission spectroscopy measurements of both single and bilayer MoS2 samples show a dramatic ...
TL;DR: This work shows that UCNPs synthesized under optimized conditions are a versatile fluorescent label for the facile development of fingerprints and can find their practical applications in forensic sciences.
Abstract: Fingerprints at crime scenes are usually latent. The powder-dusting method is the most commonly used procedure for developing latent fingerprints in forensic science. However, the traditional powder-dusting method has characteristics of low sensitivity, low contrast, high background noise, and high autofluorescence interference. To overcome the drawbacks faced by the traditional method, we first optimized an oleic acid-based solvothermal approach for the synthesis of NaYF4:Yb,Er fluorescent upconversion nanoparticles (UCNPs) with the highest possible fluorescence intensity under near-infrared (NIR) irradiation. To optimize the synthesis, we studied the effects of the reaction time, reaction temperature, and volume of oleic acid on the size, phase composition, and UC fluorescence intensity of the UCNPs. We then used the resultant UCNPs to fluorescently label the fingerprints on various smooth substrates to improve the development of latent fingerprints because the UCNPs could undergo excitation under 980 n...
TL;DR: An overview of the field of PEMs applied to the design of antimicrobial coatings is given, illustrating the large versatility of the PEM technology.
Abstract: The prevention of pathogen colonization of medical implants represents a major medical and financial issue. The development of antimicrobial coatings aimed at protecting against such infections has thus become a major field of scientific and technological research. Three main strategies are developed to design such coatings: (i) the prevention of microorganisms adhesion and the killing of microorganisms (ii) by contact and (iii) by the release of active compounds in the vicinity of the implant. Polyelectrolyte multilayer (PEM) technology alone covers the entire widespread spectrum of functionalization possibilities. PEMs are obtained through the alternating deposition of polyanions and polycations on a substrate, and the great advantages of PEMs are that (i) they can be applied to almost any type of substrate whatever its shape and composition; (ii) various chemical, physicochemical, and mechanical properties of the coatings can be obtained; and (iii) active compounds can be embedded and released in a con...