Surface Area Of Substrate Research Articles

(Energy Technology Division Graduate Student Award) Designing Polyoxometalate-Carbon Hybrid Materials for Supercapacitor Electrodes

This talk will provide an overview of our recent work in the development of supercapacitor electrode materials based on the modification of carbon substrates (MWCNTs and Activated Carbons) with custom designed polyoxometalate (POM) molecular coatings. POMs undergo fast reversible multi-electron transfer reactions, an ideal characteristic for electrochemical energy storage. When immobilized on a carbon substrate these POM molecules provide enhanced charge storage capacity due to their faradaic reactions, while the carbon material contributes mechanical support, improved conductivity, and physical capacitive effects. Different POM molecules such as PMo12O40 3- (PMo12) and PW12O40 3- (PW12) demonstrate characteristic electrochemical activity related to their chemical composition. However, we have discovered that when these molecules are combined in aqueous solutions they do not just physically mix, but instead react spontaneously to form PMo12-xWx mixed addenda chemistries with unique electrochemical properties different from that of individual PMo12 or PW12. We have also demonstrated that this mixture behaviour can be extended to additional POM combinations such as SiMo12O40 4- (SiMo12) and SiW12O40 4- (SiW12). These novel POM combinations have electrochemical properties that can be easily tuned based upon the compositions of the mixtures. This control over POM redox behavior can be used along with layer-by-layer (LbL) deposition to design molecular coatings that demonstrate desired pseudocapacitive characteristics. The best performance was achieved with a coating that superimposed a 3:1 PMo12O40 3−-PW12O40 3− mixed layer on a 1:1 GeMo12O40 4−-SiMo12O40 4− mixed layer, which resulted in a 5X capacitance enhancement over unmodified MWCNT. This dual layer electrode also demonstrated a close to rectangular CV profile due to the overlapping redox features of the POM combination (Figure 1). In addition to our work on the POM active layers, our current research on the development of alterative carbon substrates will also be discussed. While MWCNT is an effective substrate for POM modification, we have recently focused on the fabrication of less expensive activated carbon materials based on waste biomass precursors. We have developed a nanostructured carbon material based on corn-cob biomass via a simple high temperature exfoliation procedure. This exfoliated corn biochar had excellent energy storage performance, demonstrating a capacitance over 100 times higher than natural corn biochar produced without exfoliation treatment. Additionally, high surface area activated carbons from pine cone biomass were synthesized via a two-step carbonization and KOH activation method. These high surface area substrates result in carbon-POM hybrids with further enhanced specific capacitance compared to nanocarbon based materials. The capacitive performance of these different carbon-POM composites will be compared along with a discussion of how our approach can be leveraged to design the optimal hybrid material for different energy storage applications. Figure 1

Synthesis of Clustered Mn3O4 Nanoparticles through a Polymer Surfactant Mediated Route on Few-Layer Exfoliated Graphene Platelet Surface and Its Application for Electrochemical Energy Storage: Lithium-Ion Battery Anode

Composites synthesized through the deposition of Mn3O4 on graphene, carbon nanotube and other carbon based materials have attracted much attention recently as potential electrode materials for different electrochemical applications such as pseudocapacitor; Lithium-ion battery; and catalysis. The primary reason Mn3O4 is grown on these substrates in spite of having high charge storage capacity as pseudocapacitor or Lithium-ion battery electrodes on its own is to enhance its electrical conductivity and/or to impart flexibility to the electrode, which is difficult for a fully metallic electrode. Higher electrical conductivity prolongs the cycle life of an electrode. In addition, the substrate contributes capacity and thus, enhances the overall energy density of an electrode. Mn3O4 acts as a spacer and keeps graphene nanosheets separated when used as the substrate for capacitor electrode fabrication. This helps retain the high surface area of graphene nanosheets in the electrode which contributes additional capacitance. Mn3O4 supported on graphene and other carbon substrates have recently been investigated as catalyst for methanol electro-oxidation in alkaline media; CO oxidation; and Oxygen reduction reaction (ORR). High surface area substrate uniformly distributes metal particles and prevents their agglomeration and dissolution during catalytic process. In addition, high electrical conductivity of graphene and carbon substrates enhances the electronic conductivity of Mn3O4 which is of importance for superior catalytic activity. Composite of Mn3O4 combined with carbon based substrate has also found non-electrochemical application such as the removal of Pb and Cu ions from aqueous solution because of their adsorptive behaviour. A myriad of procedures have been adopted for the synthesis of Mn3O4 on graphene or other carbonaceous substrates. All of these methods involve one or more of the following factors that complicate the process, such as: long synthesis time; high synthesis temperature; use of hazardous/toxic chemicals; multistep process and the requirement for sophisticated device or highly controlled environment. In fact, the complicacies associated with the synthesis of Mn3O4 have already been acknowledged and investigations have been directed at finding relatively simpler route such as the use of microwave technique. In this research, we report the synthesis of clusters of nearly octahedral shaped Mn3O4 nanoparticles on few-layer exfoliated graphene platelet (15µm diameter, thickness 6-8 nanometer, 120-150 m2/g surface area) surface through a simple, wet-chemical, polyethyleneimine (PEI) mediated route. Few-layer exfoliated graphene platelets are ultrathin particles of graphite that can also be thought of as short stacks of graphene sheets prepared through proprietary manufacturing processes. Several grades and sizes with thicknesses ranging from 1-20 nanometers and width ranging from 1-50µm are manufactured by XG Sciences, Lansing, MI, USA. Unique manufacturing processes for these platelet materials are non-oxidizing; thus, yielding a pristine graphitic surface of sp2 carbon molecules. This makes these platelet particles especially suitable for applications requiring high electrical and thermal conductivities. The surface areas of the resulting platelets predominantly consist of the open surface areas of the graphene basal planes. The components involved in this synthesis method are manganese salts (KMnO4 and MnSO4.H2O); water; PEI; and few-layer exfoliated graphene platelet as the substrate. The synthesis is carried out at a temperature of 80°C only and in open air. Highly crystallized Mn3O4 particles, as observed by X-Ray Diffraction (XRD), can be synthesized on few-layer exfoliated graphene platelet surface. It has also been observed that PEI acts as a reducing agent and as a capping agent on a continuous network of ribbon-like Birnessite-MnO2 (IV) to produce a nearly octahedral shaped nanoparticles of Mn3O4 (II, III). It has already been mentioned that composites of Mn3O4 on graphene or other carbonaceous substrates find a myriad of applications. Thus, our research findings to synthesize few-layer exfoliated graphene platelet-Mn3O4 composite through a simple method should be of interest to a broad group of researchers. In this research, we have investigated the performance of this composite system as a Lithium-ion battery anode only. Our preliminary investigations reveal that the Mn3O4 composite synthesized through this method has just as much potential as the ones prepared through other alternative methods.

Copper Benzenetricarboxylate Metal-Organic Framework Nucleation Mechanisms on Metal Oxide Powders and Thin Films formed by Atomic Layer Deposition.

Chemically functional microporous metal-organic framework (MOF) crystals are attractive for filtration and gas storage applications, and recent results show that they can be immobilized on high surface area substrates, such as fiber mats. However, fundamental knowledge is still lacking regarding initial key reaction steps in thin film MOF nucleation and growth. We find that thin inorganic nucleation layers formed by atomic layer deposition (ALD) can promote solvothermal growth of copper benzenetricarboxylate MOF (Cu-BTC) on various substrate surfaces. The nature of the ALD material affects the MOF nucleation time, crystal size and morphology, and the resulting MOF surface area per unit mass. To understand MOF nucleation mechanisms, we investigate detailed Cu-BTC MOF nucleation behavior on metal oxide powders and Al2O3, ZnO, and TiO2 layers formed by ALD on polypropylene substrates. Studying both combined and sequential MOF reactant exposure conditions, we find that during solvothermal synthesis ALD metal oxides can react with the MOF metal precursor to form double hydroxy salts that can further convert to Cu-BTC MOF. The acidic organic linker can also etch or react with the surface to form MOF from an oxide metal source, which can also function as a nucleation agent for Cu-BTC in the mixed solvothermal solution. We discuss the implications of these results for better controlled thin film MOF nucleation and growth.

Crucial role of a nickel substrate in Co3O4 pseudocapacitor directly grown on nickel and its electrochemical properties

In this study, Co3O4 directly grown on a porous nickel substrate was successfully prepared and characterised as a potential candidate for pseudocapacitor applications. The electrochemical properties of Co3O4 were adversely affected by the sluggish charge transfer at the interface between the electrode and electrolyte and the diffusion of ions from the electrolyte to the interface. These challenges were overcome by the introduction of a high-surface-area Ni substrate for Co3O4, which improves the electrochemical performance of Co3O4; this is indicated by the excellent capacitance and low impedance. This study suggests that the electrochemical properties of several pseudocapacitive oxide materials can be tailored by increasing the surface area of the metal substrate.

Modulating the Assembly of Sputtered Silver Nanoparticles on Screen-Printed Carbon Electrodes for Hydrogen Peroxide Electroreduction: Effect of the Surface Coverage

Nanosized metallic particles are commonly used as an electrode modifier to catalyze various species, yet some of their physico-chemical characters, such as size, morphology, immobilization mode, and modification density, might affect the electrocatalytic properties of these particles. Here we engineer the diverse assemblies of silver nanoparticles on screen-printed carbon electrodes via the versatile vacuum sputtering approach, and evaluate their voltammetric behavior toward hydrogen peroxide reduction in pH 7.4. By simply modulating the sputtering time from 10s to 200s, silver assemblies with different surface coverages (defined as the ratio of the particle occupied surface area to the substrate geometric surface area) in the range of 0.38∼0.99 are exquisitely obtained. It is interestingly found that the surface coverage of the assembled silver on the disposable substrate exhibits a significant impact on the voltammetry of hydrogen peroxide electroreduction. The cathodic peak potential keeps shifting positively along with the surface coverage increasing, and the apparent peak current density normalized to the substrate surface area undergoes a volcano-type variation. When the overall peak current is normalized to the metal occupied surface area/loading content, a decreasing tendency of the specific/mass current is observed. These results suggest that the effect of the modification surface coverage should be taken into consideration when evaluating the contribution of nanosized materials to a given electrocatalytic reaction. When an appropriate compromise of the catalytic overpotential and the apparent current as well as the catalyst amount is desired for electrocatalysis, modulation of the modification surface coverage may be utilized to realize this compromise.

Structural Features of Formiline Pretreated Sugar Cane Bagasse and Their Impact on the Enzymatic Hydrolysis of Cellulose

Enzymatic digestibility of sugar cane bagasse could be greatly enhanced by Formiline pretreatment, which comprises a formic acid (FA) delignification followed by an alkaline deformylation. The FA can be easily recovered and recycled for delignification, indicating that this pretreatment is a green process for biomass fractionation. It was found that removing hemicelluloses and lignin during pretreatment contributed to the increase of cellulose accessibility; however, delignification seemed to be more important for exposing cellulose fibers. The compact cell wall structure of raw bagasse was destroyed by removing considerable parts of lignin and hemicelluloses with liberation of cellulose fibers, and the specific surface area of the pretreated substrates increased by more than 2-fold. However, formylation of cellulose took place during FA delignification, which showed significant negative impact on the initial enzymatic hydrolysis rate and enzymatic polysaccharide conversion at 120 h. Removing formyl group...

Linewidth Control and the Improved Adhesion of Inkjet-Printed Ag on Polyimide Substrate, Textured Using Near-Atmospheric Pressure Plasmas

In this paper, the effect of polyimide surface modification – using near-atmospheric pressure plasmas – on the line width and adhesion of inkjet-printed Ag was investigated by texturing and modifying the chemical composition of the polyimide surface. The polyimide surface was textured with He/O2, to increase the surface area of the polyimide substrate and it increased the water contact angle from 57 to 137°, when the textured polyimide surface was treated with a SF6 plasma after the texturing process. The textured polyimide surface also exhibited the increased adhesion strength of Ag film (by about two times), due to the increase in the contact area, as expected, according to the Wenzel model. The linewidth of the inkjet-printed Ag line decreased by about ten times from 330 µm (for the flat polyimide surface) to 23 µm (for the textured polyimide surface) in addition to having smoother line edges.

Pool boiling heat transfer enhancement using vertically aligned carbon nanotube coatings on a copper substrate

In the present study, pool boiling heat transfer experiments are performed on a bare copper surface, a sandblasted copper surface, and carbon nanotube coated copper substrates. Experiments were conducted on the substrate surface area of 14 × 14 mm2 using de-mineralized water as the working fluid. The substrate is fixed tightly on the heater block, which is embedded with six cartridge heaters of total capacity 1500 W. Heat fluxes were measured using J-type thermocouples, which were aligned vertically along the heater block and also 1 mm from the top of the substrate. The pool boiling heat transfer experiments were conducted on bare, sandblasted and vertically aligned CNT coated copper substrates. The obtained results of sandblasted and CNT coated surfaces were compared with that of the bare copper surface. A remarkable enhancement of 38% in the CHF was observed on the CNT coated surface. The CNT coated surface was found to be effective in increasing the nucleate boiling and the CHF.

Sorption equilibrium and kinetics for cyclohexane, toluene, and water on Athabasca oil sands solids

ABSTRACTThe sorption of solvents from the vapour phase to solid substrates is important in producing heavy oil and bitumen, particularly from the oil sands. We investigated the sorption and desorption equilibrium and kinetics of cyclohexane, toluene, and water on kaolinite, fine solids, and organic‐rich fine solids isolated from Athabasca oil sands over a wide range of solvent vapour concentrations using a gravimetric method. The isotherms for both adsorption and desorption of solvent vapour were determined, and the Brunauer‐Emmett‐Teller equation was used to fit the experimental data. The initial kinetic rate constants for the adsorption and desorption of solvent vapour were determined with the linear driving force model. The results were compared and discussed in terms of the type of solvent, the content of organic materials, and the surface area of the solid substrates. The results suggest that, in addition to the adsorption of solvent on mineral surfaces, the contribution from solvent partitioning in the organic materials and the porosity resulting from high amounts of organic materials are significant factors for solvent uptake and kinetic rate constants. In mixed solvent vapours, the competitive sorption of water and cyclohexane was observed in the solid substrates. However, the degree of competitiveness decreased with an increase in the content of organic materials in the substrates.

Influence of hierarchical micro-micro patterning and chemical modifications on adhesion between aluminum and epoxy

The main target in the study of aluminum-epoxy resin joints was to enhance adhesion by increasing the surface area of aluminum substrates and by chemical functionalizing the aluminum surface to provide coupling points for epoxy resin. The surface area of the aluminum substrates was increased by fabricating microscale structures and hierarchical micro-microstructures by utilizing a micro-mesh printing technique and sandblasting. The effects of silanization with 3-glycidoxypropyltrimethoxysilane (GPTMS) and of oxygen plasma treatment were also investigated. Compared to a smooth surface, the micro-mesh structures improved shear strength by 33% and the hierarchical micro-microstructures by 116%. The utilization of the oxygen plasma treatment and especially the silane modification of the aluminum substrates were found to be effective in promoting adhesion. The specimens modified by combining the chemical or energetic modification method with surface texturing tended to fracture more cohesively than the specimens having a single modification. The hierarchically patterned and plasma and silane modified specimens had so high adhesion that the aluminum substrates started to deflect during the shear strength measurements, thus preventing the evaluation of their maximum strength.

Biosurfactant: Types, Detection Methods, Importance and Applications

There are many insoluble substrates that remain unavailable for macro and micro organisms. A microorganism synthesizes surface active agents to utilize these substrates that are collectively called as biosurfactants. Biosurfactants enhances the surface area of hydrophobic water-insoluble substrates that organism utilizes it for its growth and work efficiently in process of biodegradation, bioremediation and biocontrol. Oil spilling is a distressing problem for the environment that is affecting chemical, physical and biological equilibrium of all systems. A microorganism does many miraculous jobs. In such oil spilling conditions, they are personalized to grow in environmental conditions that are rich in oil. Their ability of utilizing oil we cannot ignore that highlights its importance to utilize the hydrocarbons as sole sources of energy. The hydrocarbon-utilizing microorganisms generates surface active agent that accelerates the process that are best defined as biosurfactants. Many methods are there to check the biosurfactants potentiality of the bacterial isolates such as Hemolytic activity, Drop collapsing test, Oil spreading test, Emulsification index test, Blue agar plate or CTAB agar plate method and Hydrocarbon overlay agar method. In this paper its classification, properties, methods and significance are presented. The paper also highlights its importance in reducing the oil spills.

Sensing element for detection of polar organic vapours on the base of polyaniline-composite - Effect of substrate surface area

Conductive polymer polyaniline (PANI) was synthesized by oxidative polymerization of aniline hydrochloride as a source of aniline and ammonium persulfate as an oxidation agent. The polymerization process is relatively easy and cheap. The reaction was carried out in presence of polymer substrate, in our case polyethylene terephthalate (PET) as a representative of smooth surface substrate and polyvinylidenfluoride (PVDF) nanofibers membrane as a representative of porous substrate. Both these substrates were covered by polyaniline (PANI) and used as a sensing element for organic vapors detection. The detection was made by measuring and the record of the change of resistivity during adsorption and desorption of saturated vapors. The result shows that sensitivity decreases with increasing polarity of chosen solvent in order N,N- Dimethylformamide (DMF), N,N-Dimethylacetamide (DMAc) and Dimethyl sulfoxide (DMSO). The PANI base sensing element on PVDF substrate improves sensitivity, selectivity and it also has good reversibility and repeatability.

Gecko Adhesion on Wet and Dry Patterned Substrates.

Perhaps one of the most astounding characteristics of the gecko adhesive system is its versatility. Geckos can locomote across complex substrates in a variety of conditions with apparent ease. In contrast, many of our synthetic pressure sensitive adhesives fail on substrates that are dirty, wet or rough. Although many studies have investigated the effect of environmental challenges on performance, the interaction of multiple, potentially compromising variables is studied less often. Here we focus on substrate structure and surface water, both of which are highly relevant to the biological system and to synthetic design. To do this we utilized a highly controlled, patterned substrate (Sharklet®, by Sharklet® Technologies Inc.). This allowed us to test independently and jointly the effects of reduced surface area substrates, with a defined pattern, on adhesion in both air and water. Our results show that adhesion is not significantly impaired in air, whereas surface area and pattern significantly affect adhesion in water. These findings highlight the need to study multiple parameters that are relevant to the gecko adhesive system to further improve our understanding of the biological system and to design better, more versatile synthetics.

Rapid and Sensitive Determination of HIV-1 Virus Based on Surface Enhanced Raman Spectroscopy.

In this study, rapid and sensitive detection of human immunodeficiency virus (HIV)-1 was performed based on immunoreactions with an Au nanodot fabricated indium tin oxide (ITO) substrate using surface-enhanced Raman spectroscopy (SERS). Highly ordered Au nanodots (ca. 20 nm) were electrochemically fabricated over a large surface area (20 mm x 10 mm) of an ITO substrate using a simple deposition method with Triton X-100. On the Au nanodot surface, monoclonal antibody fragments against gp120 were selectively bound by gold-sulfur interactions. Various concentrations (35 fg/mL to 350 pg/mL) of HIV-1 virus-like particles (HIV-1 VLPs) were used for the measurements. The presence of HIV-1 VLPs was rapidly (within 5 s) and successfully determined by SERS due to specific immunoreactions on the Au nanodots without the use of labeling probes. The results showed the possibility of using SERS-related methods as a new immunoassay for the study of biomolecular interactions and detection of low viral loads. Moreover, based on its high sensitivity and chemical specificity, SERS could be used as a promising clinical tool for detecting infectious small biological components.

Development and Testing of Diglycolamide Functionalized Mesoporous Silica for Sorption of Trivalent Actinides and Lanthanides.

Sequestration of trivalent actinides and lanthanides present in used nuclear fuel and legacy wastes is necessary for appropriate long-term stewardship of these metals, particularly to prevent their release into the environment. Organically modified mesoporous silica is an efficient material for recovery and potential subsequent separation of actinides and lanthanides because of its high surface area, tunable ligand selection, and chemically robust substrate. We have synthesized the first novel hybrid material composed of SBA-15 type mesoporous silica functionalized with diglycolamide ligands (DGA-SBA). Because of the high surface area substrate, the DGA-SBA was found to have the highest Eu capacity reported so far in the literature of all DGA solid-phase extractants. The sorption behavior of europium and americium on DGA-SBA in nitric and hydrochloric acid media was tested in batch contact experiments. DGA-SBA was found to have high sorption of Am and Eu in pH 1, 1 M, and 3 M nitric and hydrochloric acid concentrations, which makes it promising for sequestration of these metals from used nuclear fuel or legacy waste. The kinetics of Eu sorption were found to be two times slower than that for Am in 1 M HNO3. Additionally, the short-term susceptibility of DGA-SBA to degradation in the presence of acid was probed using (29)Si and (13)C solid-state NMR spectroscopy. The material was found to be relatively stable under these conditions, with the ligand remaining intact after 24 h of contact with 1 M HNO3, an important consideration in use of the DGA-SBA as an extractant from acidic media.

Structural changes in lignin during integrated process of steam explosion followed by alkaline hydrogen peroxide of Eucommia ulmoides Oliver and its effect on enzymatic hydrolysis

Eucommia ulmoides Oliver (EU) wood was successively treated by a combined system based on steam explosion pretreatment (SEP) and alkaline hydrogen peroxide post-treatment (AHPP). In this case, SEP was to disrupt the lignocellulosic structure, and the subsequent AHPP process was to isolate the high-purity lignin and cellulose-rich substrates. Results showed that the lignin fractions obtained during the AHPP exhibited smaller molecular weights, narrow polydispersity, less phenolic OH groups and lower syringyl/guaiacyl ratios (S/G) than those of the milled wood lignin (SEMWL) obtained from the only steam exploded EU. NMR characterization of lignin revealed that the AHPP process has a slight effect on the composition and molecular characteristic of lignin, and the lignin isolated had lower amounts of substructures (aryl-β-ether, resinol, and phenylcoumaran linkages) as compared to those in SEMWL. Moreover, the subsequent SEP followed by AHPP process enhanced the enzymatic hydrolysis of cellulose-rich substrates to a maximum value of 91.69%. It was found that the synergistic treatment removed most of lignin, degraded hemicelluloses, and incurred a higher crystalline index and surface area of the cellulose-rich substrates as compared to the only steam explosion pretreatment. The combination of the SEP and AHPP processes is an environmentally benign and advantageous scheme for the production of high-purity lignin and cellulose-rich substrates, which will be further transformed into the value-added biomaterials and bioethanol.

Morphological differences in the mirror neuron system in Williams syndrome

Williams syndrome (WS) is a genetic condition characterized by an overly gregarious personality, including high empathetic concern for others. Although seemingly disparate from the profile of autism spectrum disorder (ASD), both are associated with deficits in social communication/cognition. Notably, the mirror neuron system (MNS) has been implicated in social dysfunction for ASD; yet, the integrity of this network and its association with social functioning in WS remains unknown. Magnetic resonance imaging (MRI) methods were used to examine the structural integrity of the MNS of adults with WS versus typically developing (TD) individuals. The Social Responsiveness Scale (SRS), a tool typically used to screen for social features of ASD, was also employed to assess the relationships between social functioning with the MNS morphology in WS participants. WS individuals showed reduced cortical surface area of MNS substrates yet relatively preserved cortical thickness as compared to TD adults. Increased cortical thickness of the inferior parietal lobule (IPL) was associated with increased deficits in social communication, social awareness, social cognition, and autistic mannerisms. However, social motivation was not related to anatomical features of the MNS. Our findings indicate that social deficits typical to both ASD and WS may be attributed to an aberrant MNS, whereas the unusual social drive marked in WS is subserved by substrates distinct from this network.

Fabrication of a Au–polystyrene sphere substrate with three-dimensional nanofeatures for surface-enhanced Raman spectroscopy

Methods for fabricating three-dimensional nanofeature arrays for surface-enhanced Raman spectroscopy (SERS) substrates were explored by combining the self-assembly of nanoscale polystyrene (PS) spheres with subsequent Au film ion sputter coating modulation. The substrate's nanoscale hot-spot features were controlled using the Au coating film thickness regulation and focused ion beam (FIB) nano-patterning regulation methods. Scanning electron microscopy and Raman spectroscopy were employed to analyze the substrate morphology and the enhancement mechanism of the three-dimensional SERS substrate. PS microspheres with diameters of 151nm and 360nm were coated with Au layers of different thicknesses ranging from 10nm to 270nm. The configuration of the Au–PS spheres can be regulated to hexagonal close packing with nanoscale V-shaped slits with a 10–20nm gap pattern. Nanoscale Au particles and clusters with a clear outline covered the surface of the PS spheres, in which the multiple-scale structures increase the specific surface area of the SERS-active substrate. Nanoscale cracks formed on the smaller Au–PS spheres with a diameter of 151nm, which also exhibited strong SERS activity. The substrate surface temperature regularly increased after Au coating, and the thermal expansion coefficient difference and PS glass transition properties were studied to explain the Au–PS spheres nanofeature configuration development. The fabricated Au–PS spheres SERS feature is a type of three-dimensional and highly ordered array, which can show Raman scattering characteristics by providing a SERS enhancement factor of greater than 107.

Direct writing and electro-mechanical characterization of Ag micro-patterns on polymer substrates for flexible electronics

There is currently a great interest in developing flexible electrodes. Such components are used in most electronic devices from displays to solar cells to flexible sensors. To date most of them are fabricated using expensive vacuum techniques, and are based on transparent conducting oxides. These oxides are not entirely compatible with flexible substrates under the application of mechanical stresses, due to their brittle nature. Therefore, there is a need to explore novel low-cost, large-area fabrication methods to deposit alternative conducting materials with enhanced electro-mechanical performance.This work focuses on Ag patterns fabricated at low temperatures (below 150°C) on flexible polyethylene naphthalate utilizing a robotic printing approach. Such lithography-free method minimizes material waste by printing exact amounts of inks on digitally predefined locations. Additionally, it allows a broad feature size range, from a few μm to a few mm, and a variety of ink viscosities for better pattern control.We investigate the synthesis and direct writing of Ag particle-based inks, patterned-on-flex as lines and grids in the μm scale. We report on a high-yield ink synthesis method (~61.6%) with controlled particle size. It is found that the electrical resistivity (1.75∗10−4Ωcm) of the patterns is in the same range with similar particle-based conductive components. The correlation between annealing temperature, microstructural evolution, and electrical performance is established. Also, the optical transmittance of the patterns can be controlled to meet specific application requirements by regulating the substrate surface area covered. Finally, the mechanical behavior under both monotonic and cyclic conditions shows a superior performance compared to brittle counterparts and underlines the potential of such metallic micro-patterns to be utilized in a wide range of flexible electronic applications. It is believed that direct writing of Ag patterns on compliant substrates may hold the key in developing the next generation of truly flexible devices.

Protective Mo2NiB2–Ni coatings by centrifugal metallothermic SHS

Cast Mo2NiB2–Ni metal-matrix composites and protective coatings thereof were fabricated by centrifugal metallothermic SHS process. The quality of SHS surfacing was found to depend on process parameters such as the mass of green mixture per unit surface area of substrate and centrifugal acceleration. The hardness of synthesized coatings was rather high and attained as large values as 800–1200 H V. Optimal conditions for deposition of high-quality protective coatings onto a steel substrate were found experimentally. The process can be recommended for practical implementation in production of cutting tools, tribological materials, molds, and deposition of protective coatings. The present results can be expected to make a theoretical background for industrial-scale manufacturing of new tungsten-free MMCs and protective coatings with valued service parameters.