Search

This research investigates the development of ultrathin polyamide (PA) desalination membranes via electrospray fabrication, balancing the trade‐offs between selectivity and permeability. The unique contribution to the improvement of desalination performance is the integration of protonated montmorillonite nanoclay (MMT‐H+) and hyperbranched amino‐polyol cellulose nanocrystals (APCNC) as co‐nanofillers during the in situ interfacial polymerization process. Synergistic effect of the nanofillers is demonstrated in the resultant spherulitic PA thin‐film nanocomposite (TFN) membrane, achieving salt rejection of up to 99.7% against simulated brackish water. Moreover, the membrane's superior boron removal efficiency at neutral pH, observed at 76.7% in a single‐stage desalination process, is attributed to the reduced membrane pore size, disruption of water‐boron association by the spherulites, and complexation and electrostatic interaction with the abundant hydroxyl and amine groups along the APCNC polymeric chains. This process eliminates the need for pH adjustment, thereby enhancing the membrane's practicality and efficiency. The findings of this study provide significant insights into the interactions between boron and the membrane surface, laying the groundwork for the development of effective TFN desalination membranes for water purification and boron removal. The implication of these findings extends beyond academic interest, offering a promising strategy for addressing the global water scarcity crisis. [ABSTRACT FROM AUTHOR]

The self‐assembly of amphiphilic molecules produces structures of diverse dimensions, encompassing micelles, tubules, lamellae, and vesicles. This study focuses on elucidating the controllability of amphiphilic lipid molecule self‐assembly in size and uniformity to facilitate our understanding of the molecular characteristics that correlate with the functions and attributes of the assembled structures. Electrospray deposition allows micropatterning of lipid molecules in conjunction with a conductive–nonconductive patterned substrate. The solvent in the sprayed mist undergoes evaporation during flight, leading to the deposition of dry lipids exclusively on the conductive regions of the substrate. This process enables homogeneous lipid micropatterning, effectively circumventing the coffee‐ring effect. Subsequent hydration of the lipid pattern triggers the spontaneous formation of a size‐controlled, unilamellar vesicle array on the substrate, spanning an area of a few square millimeters. The vesicles exhibits monodispersity, with a coefficient of variation below 8% for sizes ranging from 5 to 20 μm. The size‐controlled self‐assembly process is adaptable to various lipid compositions, thereby demonstrating that the molecular characteristics manifest in the morphological features appear as phase separation, budding, and curvature of vesicle membranes. The approach further validates its suitability for conducting time‐resolved analyses of molecular transport and ligand binding on the monodispersed vesicle array. [ABSTRACT FROM AUTHOR]

The self‐assembly of amphiphilic molecules produces structures of diverse dimensions, encompassing micelles, tubules, lamellae, and vesicles. This study focuses on elucidating the controllability of amphiphilic lipid molecule self‐assembly in size and uniformity to facilitate our understanding of the molecular characteristics that correlate with the functions and attributes of the assembled structures. Electrospray deposition allows micropatterning of lipid molecules in conjunction with a conductive–nonconductive patterned substrate. The solvent in the sprayed mist undergoes evaporation during flight, leading to the deposition of dry lipids exclusively on the conductive regions of the substrate. This process enables homogeneous lipid micropatterning, effectively circumventing the coffee‐ring effect. Subsequent hydration of the lipid pattern triggers the spontaneous formation of a size‐controlled, unilamellar vesicle array on the substrate, spanning an area of a few square millimeters. The vesicles exhibits monodispersity, with a coefficient of variation below 8% for sizes ranging from 5 to 20 μm. The size‐controlled self‐assembly process is adaptable to various lipid compositions, thereby demonstrating that the molecular characteristics manifest in the morphological features appear as phase separation, budding, and curvature of vesicle membranes. The approach further validates its suitability for conducting time‐resolved analyses of molecular transport and ligand binding on the monodispersed vesicle array.

The rapid surge in the power conversion efficiencies (PCEs) of organic photovoltaics (OPVs) calls for a simple and efficient solar tracking strategy to maintain normal incidence of light and fully use the solar energy. Here this study proposes a new solar tracking approach based on kirigami by taking the advantage of the paper‐like OPVs made on flexible substrates. The kirigami pattern is judicially designed to form three separate regions of beams, hinges, and devices. The stretching force is applied to beams, which cause out‐of‐plane deformation of the hinges, rotating the device connected to the hinges and maintaining nearly 100% optical coupling efficiency. Electrospray is used to print active layers on the pre‐cut kirigami substrates. The all‐printed kirigami OPVs achieve the highest PCE of 14.15%. Large‐area kirigami OPVs (0.62 cm2) demonstrate PCEs up to 10.19%. The kirigami OPVs are mechanically robust, showing no appreciable decrease in performance after a 20 000‐cycle stretching. This kirigami structure provides possibilities to customize the shapes of the device region to achieve more functions such as ventilation and decoration. The kirigami OPVs show satisfactory PCEs, effective solar tracking and versatile design possibilities, powerfully demonstrating the thin, light and flexible feature of OPVs. [ABSTRACT FROM AUTHOR]

An analysis is presented of the attachment of electrospray nanodroplets by larger particles in a grounded metallic tube where both are carried by a laminar air flow. Droplets and particles that get charged by attaching droplets migrate toward the tube wall under the action of the electric field induced by their charges, but they do so at different velocities owing to the disparity of their electrical mobilities. The electric currents they cause in the tube wall originate therefore in different regions of the tube, and can be separately measured by splitting the tube into two insulated segments. It is shown that, in two limiting conditions, the cross-section for droplet–particle collisions can be extracted from these measurements. • A preliminary analysis is carried out of a device intended to measure the cross-section for electrospray droplet–particle collisions in two limiting conditions of interest. • The device consists of a grounded metallic tube made of two electrically insulated segments. The tube is fed with a laminar gas flow loaded with measured fluxes of droplets and particles. • Taking advantage of the disparity between the electrical mobilities of the droplets and the particles, the collision cross-section is extracted from measurements of the electric currents in the wall of each tube segment. • The errors due to be finite value of the mobility ratio are estimated, and corrections are proposed. [ABSTRACT FROM AUTHOR]

An electrospray photolithographic patterning (EPP) process that integrates advantages of electrospray (ES) and digital light processing (DLP) for maskless fabrication of 3D porous microstructures is proposed here. First, monodisperse microparticles with controllable particle size produced by ES are deposited on a substrate to form a photoresist layer. Second, DLP exposure of the photoresist layer selectively irradiates the microparticles to form a desired pattern with complexity. Third, the repetitive steps of deposition and exposure enable layer‐by‐layer construction of a green part with embedded 3D patterns of irradiation. Finally, the irradiated microparticles are removed from the green part to form 3D particulate microstructures. With this process, freeform patterning of multiple micro‐electro‐mechanical system elements with controlled porosity, involving microfluidic channels, stamps, and power‐free pressure sensors is successfully demonstrated. The EPP process has a great technical potential for freeform and high‐throughput fabrication of multi‐layered porous microstructures in versatile applications such as micromixers, porous stamping, and microsensors. [ABSTRACT FROM AUTHOR]

We theoretically analyze the effectiveness of an electrospray of ultrafine droplets to filter out micron sized particles from a gas stream. To that end, we introduce an axisymmetric configuration where the airborne particles merge with the electrospray. The droplets attach to the particles, charging them, and both droplets and charged particles are eventually driven towards a collector by means of an electric field. The attachment process is described through a set of reaction constants based on calculated collision cross-sections, yielding particles with different charge levels. The problem involves computation of the concentrations of each type of particle, the gas flow, and the electric field due to the applied voltages and the space charge. Preliminary numerical simulations show a filtration efficiency that is above 95% for particles larger than about 2 μ m and rapidly declines for smaller particles, though this drop of the efficiency can be postponed to smaller particle sizes by decreasing the ratio of particle to electrospray fluxes or the ratio of the inlet velocity of the particle carrying gas to the velocity induced by electric forces inside the device. Pending an exhaustive numerical exploration of the parameter space of the system, these results also show that the gas flow structure, which is strongly affected by the charged particles, is key for high filtration efficiency. • Analysis of how microparticles get charged by ultrafine electrospray droplets. • Finding the cross-section of the droplet-to-particle attachment process. • CFD simulations of filtration using an electrospray of ultrafine droplets. • Studying the effect of some parameters on filtration efficiency. [ABSTRACT FROM AUTHOR]

Microsphere-based controlled release technologies have been utilized for the long-term delivery of proteins, peptides and antibiotics, although their synthesis poses substantial challenges owing to formulation complexities, lack of scalability, and cost. To address these shortcomings, we used the electrospray process as a reproducible, synthesis technique to manufacture highly porous (>94%) microspheres while maintaining control over particle structure and size. Here we report a successful formulation recipe used to generate spherical poly(lactic-co-glycolic) acid (PLGA) microspheres using the electrospray (ES) coupled with a novel thermally induced phase separation (TIPS) process with a tailored Liquid Nitrogen (LN 2 ) collection scheme. We show how size, shape and porosity of resulting microspheres can be controlled by judiciously varying electrospray processing parameters and we demonstrate examples in which the particle size (and porosity) affect release kinetics. The effect of electrospray treatment on the particles and their physicochemical properties are characterized by scanning electron microscopy, confocal Raman microscopy, thermogravimetric analysis and mercury intrusion porosimetry. The microspheres manufactured here have successfully demonstrated long-term delivery (i.e. 1 week) of an active agent, enabling sustained release of a dye with minimal physical degradation and have verified the potential of scalable electrospray technologies for an innovative TIPS-based microsphere production protocol. [ABSTRACT FROM AUTHOR]

Abstract: Images and droplet size measurements show that paper spray operates in two distinct spray modes. Mode 1 occurs in solvent-rich systems in which multiple Taylor conejets are created producing droplets of a range of sizes. Mode 2 occurs at low solvent flow rates and the higher currents (∼1uA) suggest a contribution from corona discharge. The latter experiment produces monodispersed droplet sizes. A distinguishing feature of paper spray in both modes is a fixed droplet velocity independent of droplet size. [Copyright &y& Elsevier]

Abstract: An Eulerian model is proposed for a dilute spray of electrically charged drops moving in a gas under the action of electric forces in conditions such that the fluctuations of the drop velocities about a local macroscopic value are small. The model consists of mass and momentum conservation equations for the drops and a Poisson equation for the electric potential of the macroscopic field induced by the charge of the drops and an externally applied voltage. When it is applicable, the model gives realistic results at a fraction of the cost of a Lagrangian simulation. Results are presented for the spray of liquid drops generated by a single electrospray source between plane parallel extractor and collector electrodes. The maximum flux of drops that can be passed from extractor to collector when the effect of the inertia of the drops is negligible is computed, and the minimum injection velocity required to prevent fly back of the drops toward the extractor for values of the flux above this maximum is determined as a function of an inertia parameter. Results for a spray with two different drop sizes show that, in agreement with experimental results published in the literature, the small drops are the first to fly back toward the extractor when the flow rate of liquid sprayed increases. [Copyright &y& Elsevier]

Abstract: Electrosprays, a unique physical phenomenon has in the past decade or so been investigated for several applications spanning the physical and life sciences. Recently, these electrified jets were established for directly forming self-assembled structures with a range of non-conducting nanomaterials [Physica E 33 (2006) 398]. The current work demonstrates the ability to directly form functionalised building blocks in the nano-range with conducting nanoparticulates. In the remit of these investigations, we also studied whether particulate loading in suspension has an affect on the forming of these nanoscaled self-assemblies. Thus, these results have widespread promising implications for patterning a wide range of surface topographies either as near-annular islands—or track-like structures. Hence, such nano-assemblies formed by means of this top-down approach could be explored as a bottom-up methodology for encouraging cell migration to those architectures for forming cell patterns to nano-electronics, which are a few examples, respectively. [Copyright &y& Elsevier]

Abstract: An induction charging nozzle has been developed for use with a fully hydraulic, flat fan, water spray. Charging is achieved by passing the spray between two relatively small diameter electrodes whose position can be changed to impart the maximum deposition current on a collection screen. A simple, analytic model was first derived to gain fundamental knowledge about the relationships between the variables that determine the deposition current (x and y electrode position, power supply voltage, and nozzle pressure), and to aid in the prediction of the optimum electrode location. The nozzle was then tested to verify the trends indicated by the model and test the hypotheses concerning the choice of electrode design. The model and experimental data trends matched well. The hypothesis for using small electrodes to help avoid issues associated with electrode wetting was verified. As also indicated by the model, experiments showed that decreasing the x-spacing between the electrodes and the spray resulted in an increase in deposition current; however, in the experimental case, droplet impact issues were revealed as the x-spacing became very small. The best y-location, relative to the nozzle orifice, for the electrodes was also clearly revealed. [Copyright &y& Elsevier]

The unearthing of fundamental science and technology associated with microencapsulation is an ongoing exciting scientific endeavour focused on by several scientists. Encapsulated structures (containing either a gas, molecules or materials) previously have been shown as having widespread applications across the physical and life sciences. In particular, such methodologies used for forming encapsulations in medical-related studies have shown great promise from diagnostics and imaging, to gene therapy and drug delivery which are only a few amongst several other applications. At present there are numerous 'jet-based' manifestations available for microencapsulation, these primarily root from either capillary or channel-based techniques. The driving mechanisms employed in these approaches exploit aerodynamic/pressure gradients to piezoelectricity. In this paper submerged electrosprays a multipurpose electric field driven jet-based technique is explored for forming near mono-dispersed encapsulations sized in the micrometer range. Our studies elucidate the ability to form microencapsulations containing either a gas or a micro/nanoparticulate-based material suspension as capsules sized in the ranges ∼65-80 µm, ∼8-25 µm to ∼3-14 µm, respectively. We believe this technique can significantly contribute to the microencapsulation field of research based on both the size of the generated encapsulations to the containment of immiscible high viscosity particulate-based suspensions. Furthermore our investigations show the ability to control the production of these encapsulations in terms of both their size and rate of generation with ease; hence demonstrating this electrospray-assisted microencapsulation route as having a wide range of applications. It should be noted that in its present form this technique could be explored for generating emulsions with a variety of materials especially with living organisms for applications in the clinical and biomedical areas of research. [ABSTRACT FROM AUTHOR]

This review surveys some capillary flows capable of stretching fluid interfaces down to the micrornetric dimension and below. These types of flows have become the basis for attractive techniques to produce monodisperse micro- and nanoparticles with either simple or core-shell structure (micro- and nanocapsules, coaxial nanofibers, and hollow nanofibers). These techniques enable precise control on the particle mean size. We also review the basic physics of the flow and the dimensionless parameters that govern these capillary flows. Some examples of the types of particles produced by a few devices are also presented. [ABSTRACT FROM AUTHOR]

Limited to nonvaporizing spray cases, this work discusses the transport of charged droplets within a cylinder of a motored axisymmetric model electrosprayed direct injection spark ignition (eDISI) engine with electrified walls. The concept engine investigated here is assumed to operate with an electrostatic atomizer previously studied for application in fuel burners [Yule et al., 1994, Fuel, 74(7), pp. 1094-1103]. A split/multiple injection strategy is employed in which three pulses of 5 mg each are made at crank angles of 80, 150 and 300 deg ATDC of the intake, which fall within the intervals for stable combustion of either early or late injection modes of operation of DISI engines [Jackson et al., 1997, SAE Paper No. 970543]. The direct Simulation Monte Carlo (DSMC) approach embodied in an in-house CFD research code is used to simulate the discrete phase flow with the electrical charge distribution for different instants within the computational cells being computed by simple addition of the droplet charges residing in particular cells at particular instants of time. It is shown in the half engine cycle investigated that the use of charged sprays in eDISI engines may help to reduce the in-cylinder wall-wetting phenomenon. In addition, pockets of highest electrical charge are found to populate the region near the spark plug by 345 deg CA, which may be a path for improved combustion efficiency. [ABSTRACT FROM AUTHOR]

Abstract: A concentrated nanoparticulate-based ethylene glycol suspension was prepared and electrosprayed at optimum and stable cone-jet mode conditions. Using laser spectroscopy, the droplets were measured and found to range within ∼0.23–3.8μm. In parallel to spectroscopy-assisted sizing, a volume equivalence route for estimating droplet sizes was carried out by measuring contact angles and diameters of the deposits. The electrosprayed nanosuspension relics were examined using optical and transmission electron microscopy. These deposits were further characterized using energy-dispersive X-rays and selected area electron diffraction. Simultaneously deposits were formed by a controlled route through needle deposition without the presence of an electric field. The structures formed in this non-electric field driven route are compared with those formed with electric fields. Thus, elucidating electrosprays as a competing nanofabrication route for forming self-assemblies with a wide range of nanomaterials in the nanoscale for top-down based bottom-up assembly of structures. [Copyright &y& Elsevier]

The calculated effects on injected charged sprays of dielectric and conductive in-cylinder wall materials are presented for a half-cycle of an axisymmetric flow model direct-injection spark-ignition (DISI) engine. A plain orifice electrostatic atomizer, previously used in experiments for application in fuel burners, is embodied into the EPISO code and this is assumed to pump a charged spray while working at moderate pressures of 5 MPa and fuel deliveries of 5 cm3/s, the maximum rates currently reported in electrostatic atomization of hydrocarbons. The transition mode operation of DISI engines is selected for the study and this consists of multiple pulses of 5 mg each, occurring at 80, 150, and 300° crank angle with the engine running at 3000 r/min. In the case of the third pulse, which impinges on the piston surface, the wall impaction model of Park and Watkins is used particularly when an electric potential of 1 kV is applied on this surface for it helps to reduce excessive fuel film build-up. Particles impinging on the cylinder roof and liner are treated with the stick impaction model of Naber and Reitz. A simple axisymmetric engine geometry of flat piston and cylinder heads is considered and computations of an uncharged spray are taken as a reference case. It is found in the study, firstly, that charge improves mixture preparation when dielectric in-cylinder surfaces are used, secondly, that the need for charge drainage in metallic surfaces produces poor spray characteristics in comparison with an ideal charged spray with boundary electric fields (this is shown by the large impingement of drop parcels relative to an ordinary spray as well as to a charged spray with electric boundary fields) and, thirdly, that charge reduces the fuel film thickness on the piston surface during late injection. [ABSTRACT FROM AUTHOR]

An experimental study of polarity inversion effects in electrohydrodynamic spraying is developed by characterizing the several atomization regimes that can be observed by varying liquid flow rate and applied voltage, n-Heptane, doped with an antistatic additive, is atomized in a classical needle-to-plate system. The study allows for the determination of two-dimensional maps of the stability regimes occurring by varying the controlling parameters. These maps have been obtained by comparison of results of direct visualization, by means of a digital camera, and Particle Dynamics Analyzer (PDA) measurements of droplet size and velocity components. Results show that occurrence of the regimes is not qualitatively influenced by polarity inversion, but in the negative polarity case any modification on spraying modes needs higher variation in applied voltage, and so the regimes are stable in larger voltage ranges. [ABSTRACT FROM AUTHOR]

Butanol produced from agricultural sources is emerging as a potentially renewable biofuel for use in engine applications. In this work, butanol electrostatic sprays were established within a narrow region of low flow rates. Spray phenomenology was investigated through high-speed visualization for the low flow rate conditions in the vicinity of the lowest voltage for which electrosprays (e-sprays) could be sustained. Spray structure was studied through droplet size and velocity measurements for a combination of conditions, performed by using phase Doppler anemometry. Combined with high-speed spray visualization, these measurements revealed a stable e-spray operation with narrow droplet size and velocity distributions; i.e., spray behavior was close to monodisperse. A similarity analysis was performed to develop an empirical expression correlating appropriately dimensionless average diameter, flow rate, and applied voltage. [ABSTRACT FROM AUTHOR]