Electrospray Deposition Research Articles

Electrospray Deposition of Cellulose Nanofibers on Paper: Overcoming the Limitations of Conventional Coating.

While the potential of cellulose nanofibers to enhance the mechanical and barrier properties of paper is well-known, there are many uncertainties with respect to how to apply them. In this study, we use not only bulk addition of micro-/nanofibers and bar coating with oxidized nanofibers, but also a combination of these and, as a novel element, electrospray deposition of nanofiber dispersions. Characterization involved testing the strength of uncoated and coated paper sheets, their resistance to air flow, their Bendtsen roughness, and their apparent density, plus visualization of their surface and cross-sections by scanning electron microscopy. As expected, bulk addition to the unrefined pulp was sufficient to attain substantial strengthening, but this enhancement was limited to approximately 124%. Following this, surface addition by bar coating improved air resistance, but not strength, since, as applying nanocellulose at high consistency was technically unfeasible, this was performed several times with detrimental drying stages in between. However, replacing bar coating with electrospraying helped us overcome these apparent limitations, producing enhancements in both barrier and tensile properties. It is concluded that electrosprayed nanofibers, owing to their uniform deposition and favorable interactions, operate as an effective binder between fibers (and/or fines).

Direct and controlled device integration of graphene oxide on Quartz Crystal Microbalance via electrospray deposition for stable humidity sensing

Integration of advanced and functional materials onto conventional sensing platforms can improve the device performances and even discover new applications. For piezoelectric resonant sensors, an addition of sensing materials can induce damping and hinder a stable device operation. Hence, the development of efficient method for materials integration is important to ensure high-performance and reliable sensor operation. This work presents a direct and precisely controlled integration of graphene oxide (GO) using the electrospray deposition (ESD) onto a 10 MHz Quartz Crystal Microbalance (QCM) for humidity sensing. The proposed ESD method achieves a high mass resolution of a few nanograms. Moreover, the GO uniformly coats across the sensing electrode region as it acts as a ground electrode during ESD. The proposed ESD method also works for a wide range of nanomaterials, such as carbon nanotubes, tin oxide, and silicon carbide micro-and nano-powders. Compared to the conventional drop-casting and dip coating approaches, our method ensures minimal GO agglomeration, resulting in a stable QCM-oscillator operation in a wide range of relative humidity from 11% to 97%. The measurement sensitivity increases with an amount of GO, but less GO results in better noise and detection limit performances. The results shed light on the importance of selecting an optimal amount of sensing materials for stable sensor operations.

Controlled Synthesis of Well-Defined Polyaminoboranes on Scale Using a Robust and Efficient Catalyst.

The air tolerant precatalyst, [Rh(L)(NBD)]Cl ([1]Cl) [L = κ3-(iPr2PCH2CH2)2NH, NBD = norbornadiene], mediates the selective synthesis of N-methylpolyaminoborane, (H2BNMeH)n, by dehydropolymerization of H3B·NMeH2. Kinetic, speciation, and DFT studies show an induction period in which the active catalyst, Rh(L)H3 (3), forms, which sits as an outer-sphere adduct 3·H3BNMeH2 as the resting state. At the end of catalysis, dormant Rh(L)H2Cl (2) is formed. Reaction of 2 with H3B·NMeH2 returns 3, alongside the proposed formation of boronium [H2B(NMeH2)2]Cl. Aided by isotopic labeling, Eyring analysis, and DFT calculations, a mechanism is proposed in which the cooperative "PNHP" ligand templates dehydrogenation, releasing H2B═NMeH (ΔG‡calc = 19.6 kcal mol-1). H2B═NMeH is proposed to undergo rapid, low barrier, head-to-tail chain propagation for which 3 is the catalyst/initiator. A high molecular weight polymer is formed that is relatively insensitive to catalyst loading (Mn ∼71 000 g mol-1; Đ, of ∼ 1.6). The molecular weight can be controlled using [H2B(NMe2H)2]Cl as a chain transfer agent, Mn = 37 900-78 100 g mol-1. This polymerization is suggested to arise from an ensemble of processes (catalyst speciation, dehydrogenation, propagation, chain transfer) that are geared around the concentration of H3B·NMeH2. TGA and DSC thermal analysis of polymer produced on scale (10 g, 0.01 mol % [1]Cl) show a processing window that allows for melt extrusion of polyaminoborane strands, as well as hot pressing, drop casting, and electrospray deposition. By variation of conditions in the latter, smooth or porous microstructured films or spherical polyaminoboranes beads (∼100 nm) result.

Highly efficient patterning technique for silver nanowire electrodes by electrospray deposition and its application to self-powered triboelectric tactile sensor

A patterned transparent electrode is a crucial component of state-of-the-art wearable devices and optoelectronic devices. However, most of the patterning methods using silver nanowires (AgNWs), which is one of the outstanding candidate materials for the transparent electrode, wasted a large amount of unused AgNWs during the patterning process. Here, we report a highly efficient patterning of AgNWs using electrospray deposition with grounded electrolyte solution (EDGE). During electrospray deposition, a patterned electrolyte solution collector attracted AgNWs by strong electrostatic attraction and selectively deposited them only on the patterned collector, minimizing AgNW deposited elsewhere. The enhanced patterning efficiency was verified through a comparison between the EDGE and conventional process by numerical simulation and experimental validation. As a result, despite the same electrospray deposition conditions for both cases except for the existence of the electrolyte solution collector, the coverage ratio of AgNWs fabricated by the EDGE process was at least six times higher than that of AgNWs produced by the conventional process. Furthermore, the EDGE process provided high design flexibility in terms of not only the material of the substrate, including a polymer and a ceramic but also the shape of the substrate, including a 2D flat and 3D curved surface. As an application of the EDGE process, a self-powered touch sensor exploiting the triboelectric effect was demonstrated. Thus, the EDGE process would be utilized in further application in wearable or implantable devices in the field of biomedicine, intelligent robots, and human–machine interface.

Interlaminar fracture toughness properties of hybrid glass fiber-reinforced composite interlayered with carbon nanotube using electrospray deposition

Abstract The electrospray deposition (ESD) method was used to deposit carbon nanotubes (CNTs) onto the surface of glass fiber (GF). The morphology of the hybrid CNTs-GF was analyzed using a field emission scanning electron microscope, and the images indicated that the CNTs were uniformly and homogenously deposited onto the GF’s surface. Laminated composite based on GF and hybrid CNTs-GF were then fabricated via vacuum-assisted resin transfer molding. The mode I interlaminar fracture toughness was measured using the double cantilever beam test method. The hybrid CNTs-GF showed a 34% increase in fracture toughness relative to the control sample. The mechanism of interlaminar fracture toughness enhancement was elucidated via fractography, where fiber bridging, adhesive and cohesive failures, hackles, and coarse matrix surface were observed along the crack pathways.

Water stable colloidal lignin-PVP particles prepared by electrospray

In this study, electrospray deposition has been used as a method to prepare lignin submicron spherical particles. Regularities of electrospraying of lignin solutions in DMSO were revealed. The influence of voltage, distance between electrodes, feed rate, temperature and concentration of lignin solution on the morphology, size and polydispersity of the obtained particles was determined. SEM, IR, TG-DSC, elemental analysis, dynamic light scattering, Zeta potential and nitrogen sorption were used to characterize the particles and to determine their properties. The aqueous colloidal solutions of the submicron particles of lignins from various plant sources were stabilized by preparing the lignin/polyvinylpyrrolidone polymeric complexes.

Crack‐free cathode of intermediate‐temperature solid oxide fuel cells via electrospray deposition

AbstractCracks and delamination primarily revealed in the microscale‐thick cathode have been known as the major cause of increasing the polarization resistance and inhibiting the low‐temperature operation of solid oxide fuel cells (SOFCs). Besides, these defects were originated from the polymer dispersant, essential for the fabrication of the bulk cathode layer. Herein, we manufactured a crack‐free cathode layer by optimizing the deposition temperature (Tdep) of the powder‐suspension electrospray deposition (ESD) process through thermal characterization of polyvinylpyrrolidone (PVP), a polymer used in the slurry of ESD. SOFCs with the cathode deposited at the glass transition temperature of PVP resulted in a maximum power density of 0.481 W/cm2, 37% and 39% improved than those with the cathode deposited at Tdep = 25 and 200℃, respectively, at 650℃. Furthermore, the effect of uniformly dispersed morphology of cathode without defects was demonstrated by the reduction of polarization resistance through electrochemical impedance spectroscopy analysis.

Exceptionally High Blocking Temperature of 17 K in a Surface-Supported Molecular Magnet.

Single-molecule magnets (SMMs) are among the most promising building blocks for future magnetic data storage or quantum computing applications, owing to magnetic bistability and long magnetic relaxation times. The practical device integration requires realization of 2D surface assemblies of SMMs, where each magnetic unit shows magnetic relaxation being sufficiently slow at application-relevant temperatures. Using X-ray absorption spectroscopy and X-ray magnetic circular dichroism, it is shown that sub-monolayers of Dy2 @C80 (CH2 Ph) dimetallofullerenes prepared on graphene by electrospray deposition exhibit magnetic behavior fully comparable to that of the bulk. Magnetic hysteresis and relaxation time measurements show that the magnetic moment remains stable for 100 s at 17 K, marking the blocking temperature TB(100) , being not only in excellent agreement with that of the bulk sample but also representing by far the highest one detected for a surface-supported single-molecule magnet. The reported findings give a boost to the efforts to stabilize and address the spin degree of freedom in molecular magnets aiming at the realization of SMM-based spintronic units.

Manganese vanadium sulfate-oxide cylindrical core-shell heterostructures by electro-spray deposition on graphite foil for Li+ ion intercalation

Heterostructure based on metal sulfides and oxides nanomaterials can be relevant to the charge storage devices. Here, we show that Mn(CH3COO)2·4H2O and VOSO4·xH2O can react in ethanol/water droplets generated by an electric field assisted spray system, so that MnSx-VSx/MnzV2O5 heterostructures in the shape of nanometric cylindrical particles can be deposited on a graphite foil substrate. The composite material phases were detected by several microscopies and microscopic probes spectroscopies, i.e., micro-Raman and scanning X-ray photoemission microscopy. The nanometric cylindrical particles were relatively homogenously distributed throughout the film covering the graphite foil. Film thickness modulation on surface was calculated between 100 and 300 nm range. We show that the segregation of MnV-O and MnV-S relative abundance in the internal and external volume of the cylindrical nanoparticles respectively, can be exploited during faradaic and non-faradaic processes in charge/discharge.

Evaluation of electrosprayed graphene oxide coatings for elemental analysis by thin film microextraction followed by Laser-induced Breakdown Spectroscopy detection

In this work, a solid phase microextraction procedure, denoted as Thin Film Microextraction (TFME), was combined with Laser-induced Breakdown Spectroscopy for the detection of several analytes in aqueous solutions (Cu, Cr, Ni and Pb). The adsorbent films, consisting of a thin layer of graphene oxide deposited on glass substrates, were generated by using the electrospray deposition technique (ESD). Several parameters affecting the quality and shape of the films resulting from the ESD process were studied, and the morphology and adsorption capacity of the films were evaluated. The generated films were used for extraction of the target analytes from aqueous solutions and, after extraction, the analytes-enriched adsorbents were analysed by LIBS without the need of any desorption or elution step. In order to assess the analytical capability of the TFME-LIBS procedure, different analytical figures of merit of the proposed TFME-LIBS methodology were evaluated. The obtained limits of detection were 14 μg kg−1 for Pb and 15 μg kg−1 for the rest of the tested analytes. Measurement repeatability was better than 4% RSD at low concentration level (20 μg kg−1) but deteriorated by increasing the concentration level at 100 μg kg−1, with %RSD ranging from 3.6% (Cr) to 24% (Pb). Method trueness, evaluated from the analysis of a real sample of bottled water, led to recovery values in the range 85%–106%.

Electrospray Deposition: A Breakthrough Technique for Proton Exchange Membrane Fuel Cell Catalyst Layer Fabrication

This Spotlight article presents the state-of-the-art of electrospray deposition technique applied to the fabrication of proton exchange membrane fuel cell (PEMFC) components, mainly focusing on catalyst layers in gas diffusion electrodes. The atomization of a suspension of particles over a substrate under the influence of a strong electric field results in the growth of a film with macroporous morphology and many interesting properties. This so-called electrospray deposition has reported many noteworthy beneficial effects for the fabrication of the catalyst layers of gas diffusion electrodes of PEMFCs. The electrosprayed catalyst layers prepared from suspensions of catalyst particles and ionomers present a dendritic macroporous morphology with superhydrophobic character that improves the water management inside the cell and increases the performance by ∼20% with respect to standard electrodes prepared by airbrushing. Other interesting effects observed with electrosprayed catalyst layers are increased catalyst utilization and water absorption capabilities of the ionomer, improved performance under nonhumidified conditions, and a reduction in catalyst degradation. In addition, the electrospray deposition decreases platinum losses during fabrication thanks to the attractive electrostatic forces between the ion mist and the substrate compared with regular ink-based spray methods.

Coupling sol-gel with electrospray deposition: Towards nanotextured bioactive glass coatings

For the first time, the sol-gel method was coupled with electrostatic spray deposition (ESD) to fabricate nanotextured bioactive glass (BG) coatings with a controlled microstructure in a one-pot-process. Three BG compositions belonging to the SiO2-CaO-P2O5 system (S85, S75, and S58) were homogeneously deposited on metallic Ti6Al4V substrates starting from the atomization of precursor solutions. All coatings displayed an amorphous character, as confirmed by XRD. A wide variety of innovative BG morphologies were obtained, tuning the key parameters of ESD, leading from highly porous coral-like to compact reticular-type coatings. The bioactivity, in terms of apatite formation, of as-deposited coatings was tested by immersion in simulated body fluid solution. Textural properties were found to play an important impact in its biological performance. Highly porous ESD-coatings exhibited remarkable bioactivity for S75 and S58 compositions, compared with more compacted ones of equal formulations. S85 composition was found extremely reactive regardless of the coating microstructure.

Fabrication of Temperature- and Humidity-Independent Silver Nanoparticle's Carbon Composite-Based Strain Sensor Through Additive Manufacturing Process.

A highly sensitive low-cost strain sensor was fabricated in this research study based on microdispensing direct write (MDDW) technique. MDDW is an additive manufacturing approach that involves direct deposition of functional material to the substrate. The devices were printed directly onto a polymeric substrate by optimizing the fabrication parameters. A composite of silver and carbon was used as active sensor material where both materials in the composite have opposite resistance temperature coefficients. The ratio of materials in the composite was selected so that the effect of temperature on the resistance of overall composite was canceled out. This resulted in achieving temperature compensation or inherent independence of the strain sensor resistance on temperature without requiring any additional sensors and components. The sensor was further encapsulated by electrospray deposition, which is also an additive manufacturing approach, to eliminate the effect of humidity as well. Electrical and morphological characterizations were performed to investigate the output response of the sensors and their physical and structural properties. An analog signal conditioning circuit was developed for seamless interfacing of the sensor with any electronic system. The sensor had an excellent gauge factor of 45 and a strain sensitivity of 45 Ω/μɛ that is higher than most of the conventional strain sensors. The sensor's response showed excellent temperature and humidity compensation reducing the relative effect of temperature on the resistance by ∼99.5% and humidity by ∼99.8%.

Influence of electrospray deposition on C60 molecular assemblies.

Maintaining clean conditions for samples during all steps of preparation and investigation is important for scanning probe studies at the atomic or molecular level. For large or fragile organic molecules, where sublimation cannot be used, high-vacuum electrospray deposition is a good alternative. However, because this method requires the introduction into vacuum of the molecules from solution, clean conditions are more difficult to be maintained. Additionally, because the presence of solvent on the surface cannot be fully eliminated, one has to take care of its possible influence. Here, we compare the high-vacuum electrospray deposition method to thermal evaporation for the preparation of C60 on different surfaces and compare, for sub-monolayer coverages, the influence of the deposition method on the formation of molecular assemblies. Whereas the island location is the main difference for metal surfaces, we observe for alkali halide and metal oxide substrates that the high-vacuum electrospray method can yield single isolated molecules accompanied by surface modifications.

Transformation of Nanodiamonds to Onion-like Carbons by Ambient Electrospray Deposition

Onion-like carbons (OLCs) are a class of fullerene-like circular nanoallotropes of carbon, typically synthesized from nanodiamond (ND) via thermal annealing, plasma spraying, and laser ablation. These methods require high temperature, high vacuum, or inert gas. Here, we report an ambient electrospray deposition (AESD) process to transform NDs (11 ± 1 nm in size) into OLCs (50 ± 13 nm in size) in water. Transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) were used for the characterization of NDs and OLCs. High-resolution TEM images showed an increased interplanar spacing from ND (0.23 nm) to OLC (0.39 nm). Raman spectra showed a shift in the ND peak from 1336 cm–1 to D-band at 1349 cm–1, and XPS quantitatively estimated an increase in the graphitization ratio (sp2/sp3) from 0.95 to 3.16 after AESD. Comparison of electrospray with sonic spray confirmed that such a transformation required an external voltage as well. AESD was also performed for NDs dispersed in ethanol and acetonitrile, which showed a solvent-dependent transformation.

High-Efficiency Electrospray Deposition Method for Nonconductive Substrates: Applications of Superhydrophobic Coatings.

When highly insulating materials are used as substrates for electronic devices, manufacturing yields become worse, and electronic components are often damaged due to undissipated electrostatic charges on such substrates. In the case of electrospray deposition, the problem of undissipated charges is particularly vexing. If charges accumulated on the substrate are not properly compensated, a repulsive force is generated against the incoming charged droplets, which negatively affects the uniformity and deposition rate of the coating layer. In order to overcome this limitation, we demonstrated a new electrospray method, which can significantly increase the deposition efficiency even in the presence of accumulated charges on nonconductive substrates. A highly reliable superhydrophobic layer was uniformly deposited on highly insulating substrates, including printed circuit board (PCB), polyester (PET), and polyimide (PI) substrates.

Electrosprayed calcium silicate nanoparticle-coated titanium implant with improved antibacterial activity and osteogenesis

To ensure clinical success, the implant and the surrounding bone tissue must not only be integrated, but also must not be suspected of infection. In this work, an antibacterial and bioactive nanostructured calcium silicate (CaSi) layer on titanium substrate by an electrospray deposition method was prepared, followed by annealing at 700, 750 and 800 °C to improve the bonding strength of the CaSi coating. The phase composition, microstructure and bonding strength of the CaSi coatings were examined. Human mesenchymal stem cells (hMSCs), Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) species were used to analyze the osteogenic and antibacterial activity of the coatings, respectively. Experimental results showed that the as-prepared CaSi coating was mainly composted of β-dicalcium silicate phase with a particle size of about 300 nm. After annealing, the thickness of the oxidation reaction layer increased obviously from 0.3 μm to 1 μm with increase in temperature, which was confirmed by the cross-sectional morphology and element depth profile. The bonding strength of the coating annealed at 750 °C (19.0 MPa) was significantly higher (p < 0.05) than that of the as-prepared coating (4.4 MPa) and the ISO 13,779 standard (15 MPa). The results of antibacterial efficacy and stem cell osteogenesis consistently elaborated that the 750 °C-annealed coating had higher activity than the as-prepared coating and the Ti control. It is concluded that after annealing at 750 °C, the CaSi nanoparticle-coated Ti implant had good bond strength, osteogenic and antibacterial activity.

Enhanced flexural strength of carbon nanotubes‐glass fiber epoxy composite laminates using an electrospray deposition technique

AbstractThe electrospray deposition technique (ESD) was used to coat carbon nanotubes (CNTs) uniformly on the surface of glass fiber (GF) and to increase the flexural strength of CNTs‐GF epoxy composite laminate. The deposition of CNTs on the GF surface has been optimized by the applied voltage and spray time. The deposited CNTs on the GF surface showed a well dispersed and homogeneous coating. Implementing optimized ESD in the fabrication of composite laminate caused a 25.26% to 59.28% improvement of flexural performance in CNTs‐GF composite laminate. The dispersion of CNTs was characterized by using a digital microscope, a field emission scanning electron microscope (FESEM), and a transmission electron microscope (TEM). The result revealed that the applied voltage had an impact on the well‐dispersed coated CNTs, while the spray time affected the flexural output.

Reliable sensors based on graphene textile with negative resistance variation in three dimensions

The weft-knitted reduced graphene oxide (r-GO) textile that is made up of many conductive r-GO coated fibers was successfully prepared dependent on the electrospray deposition technique. Interestingly, the r-GO textile presents negative resistance variation not only in axial direction as the pressure increases but also in transverse direction as the lateral stretch increases which makes it has the advantage to fabricate the reliable sensors based on strain-resistance effect. The transverse-strain and pressure sensors based on the r-GO textiles all show the excellent sensing characteristics such as high sensitivity, reliability, and good durability, etc. The maximum gauge factors (GF) of the transverse-sensor are 27.1 and 153.5 in the x- and y-direction, respectively. And the practical detection range can up to 40% in the x-direction and 35% in the y-direction, respectively. The r-GO textile pressure sensor also shows high sensitivity for a broad pressure range that with a GF up to 716.8 kPa−1 for less than 4.5 kPa region and still has more sensitive pressure sensing characteristics even the pressure goes up to 14 kPa. Based on those good performances of r-GO textile sensors, its potential applications in human body states monitoring have been studied.

Challenges in Solvent-Free Methods for Manufacturing Electrodes and Electrolytes for Lithium-Based Batteries.

With the ever-growing energy storage notably due to the electric vehicle market expansion and stationary applications, one of the challenges of lithium batteries lies in the cost and environmental impacts of their manufacture. The main process employed is the solvent-casting method, based on a slurry casted onto a current collector. The disadvantages of this technique include the use of toxic and costly solvents as well as significant quantity of energy required for solvent evaporation and recycling. A solvent-free manufacturing method would represent significant progress in the development of cost-effective and environmentally friendly lithium-ion and lithium metal batteries. This review provides an overview of solvent-free processes used to make solid polymer electrolytes and composite electrodes. Two methods can be described: heat-based (hot-pressing, melt processing, dissolution into melted polymer, the incorporation of melted polymer into particles) and spray-based (electrospray deposition or high-pressure deposition). Heat-based processes are used for solid electrolyte and electrode manufacturing, while spray-based processes are only used for electrode processing. Amongst these techniques, hot-pressing and melt processing were revealed to be the most used alternatives for both polymer-based electrolytes and electrodes. These two techniques are versatile and can be used in the processing of fillers with a wide range of morphologies and loadings.