Recent advancements in the use of aerosol-assisted atmospheric pressure plasma deposition

Atmospheric pressure plasma allows for the easy modification of materials' surfaces for a wide range of technological applications. Coupling the aerosol injection of precursors with atmospheric pressure plasma largely extends the versatility of this kind of process; in fact solid and, in general, scarcely volatile precursors can be delivered to the plasma, extending the variety of chemical pathways to surface modification. This review provides an overview of the state of the art of aerosol-assisted atmospheric pressure plasma deposition. Advantages (many), and drawbacks (few) will be illustrated, as well as hints as to the correct coupling of the atomization source with the plasma to obtain specific coatings. In particular, the deposition of different organic, hybrid inorganic-organic and bioactive nanocomposite coatings will be discussed. Finally, it will be shown that, in particular cases, unique core-shell nanocapsules can be obtained

Depósito de capas superhidrófobas de carbón mediante electrospray: aplicación en pilas de combustible de membrana protónica

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Químicas, Departamento de Ingeniería Química, leída el 29/10/2019Fuel cells are electrochemical devices that allow the production of clean, safe and renewable electrical energy. Facing the uncertainty of the upcoming end of the oil era, fuel cells are highly regarded as strong candidates for future portable, transportation and stationary applications. In particular, proton exchange membrane (PEM) fuel cells use hydrogen fuel to produce energy with high efficiency and no greenhouse gasses emission. However, a widespread market deployment is limited by the cost and durability of the components, especially the catalyst layers that requires platinum. To overcome these problems, among other approaches, the use of more efficient methods to prepare PEM fuel cell catalyst layers is studied. Electrospray is a method of liquid atomization based on the ejection of a solution or suspension under the influence of a strong electric field, without any additional physical force playing a role in the atomization process. It is a suitable technique to fabricate thin films of controlled morphology from colloidal suspensions of catalyst particles ('catalytic inks'), leading to particle monodispersity and homogeneous distribution on the substrate. Film morphology and properties strongly depend on particles disposition and stacking upon arrival to the substrate, so electrospray deposition allows the production of films of excellent quality, reducing the number of voids, flaws and cracks, and ensuring a homogenous thickness throughout the surface of the films. Electrospray is also very appropriate for depositing expensive materials, like platinum-based catalysts, because it allows high deposition efficiency of the target material, with minimal losses compared with regular ink-based methods...Las pilas de combustible son dispositivos electroquímicos que permiten una producción de energía eléctrica limpia, renovable y de forma segura. La incertidumbre que provoca el inminente fin de la era del petróleo, hace que las pilas de combustible sean consideradas como firmes candidatas para ser utilizadas en aplicaciones portátiles, estacionarias o de transporte. En particular, las pilas de combustible de membrana protónica emplean hidrógeno como combustible para producir energía eléctrica con una gran eficiencia de conversión sin producir gases de efecto invernadero. Sin embargo, la penetración de esta tecnología en el mercado está limitada por el coste y la durabilidad de sus componentes, especialmente de los catalizadores, dado que se fabrican utilizando platino. Actualmente, para superar estas limitaciones, la investigación en pilas de combustible se centra, entre otras soluciones, en el uso de métodos más eficientes para la preparación de capas de catalizador. El electrospray es un método de atomización de líquidos que se basa en la eyección de una disolución (o suspensión) bajo la influencia de un campo eléctrico, sin que ninguna otra fuerza participe en el proceso de atomización, siendo adecuada para fabricar capas delgadas de morfología controlada a partir de suspensiones coloidales de catalizador. Las propiedades y la morfología de las capas dependen fundamentalmente de la disposición de las partículas y de su ordenamiento al llegar al sustrato, por lo que el electrospray permite la fabricación de láminas de gran calidad, espesor homogéneo y bajo número de defectos. Además, es una técnica especialmente apropiada para materiales de alto coste ya que el proceso de depósito tiene una alta eficiencia, con pérdidas mínimas de material en comparación otros métodos...Depto. de Ingeniería Química y de MaterialesFac. de Ciencias QuímicasTRUEunpu

Electrospray Systems And Methods

Electrospray systems, electrospray structures, removable electrospray structures, methods of operating electrospray systems, and methods of fabricating electrospray systems, are disclosed.Georgia Tech Research Corporatio

Electro-Hydrodynamic Spot-Spray Application of Food-Grade Oil & Emulsifier Blends As a Release Agent in Baking

In industrial baking, vegetable oil is used as a release agent for bread depanning. The conventional process of applying oil uses pressure and shear to atomize the oil. This works but generates over-spray and, thus, creates a sanitation problem and a potential food safety risk. The objective of this research project is to determine if the four major commercially available vegetable oils (Palm oil, Soybean Oil, Rapeseed oil, Sunflower Oil) can be made, by the introduction of an emulsifier/surfactant, to carry an electrical charge greater than the Rayleigh point so that they can be electro-hydrodynamically (EHD) atomized. Coulombic attraction pulls the atomized liquid to the target without the problem of over-spray. To accomplish this, each base oil was blended with a surfactant (Lecithin, Polysorbate, Propylene Glycol) at concentrations of 5% and 10%. The solution was sprayed through a capillary tube (19ga, 22ga) in a spot spray mode onto oil sensitive paper at 25kV and 50kV at varying temperatures and pressures. An ANOVA of the DOE structured experiment was performed to analyze the inputs (concentration, voltage, temperature, and pressure) relative to the outputs (droplet count, droplet size, coverage area, and sample weight) to determine the performance of the experiment at different interaction points.Twenty-four separate experiments involving 865 individual tests provided the data to determine EHD viability for each oil and emulsifier blend. The criteria of average droplet count >200/in2, average droplet size <1mm2, average coverage area between 15%-60%, and average sample weight <0.2g was used as a minimum target for success. Every experimental group tested with a 22ga capillary tube met or exceeded the target. Tests using the 19ga capillary produced generally poor results. From this, it was determined that energy density relative to mass flow was a determining factor in successful EHD atomization. Energy density relative to mass flow, at the given input 2.5 and 5 Joules followed the exponential regression of respectively Ed=6ṁ(-1.004)·102 and Ed=6ṁ(-1.004)·104 respectively. Based on the success of all four base oils with all three emulsifiers, it is reasonable to assume that other oils/emulsifiers might follow the same energy density curve.Biosystems and Agricultural Engineerin

Microbubbling and microencapsulation by co-axial electrohydrodynamic atomization

Microbubbles coated with polymers or surfactants have been used in medical imaging for several years as ultrasound contrast agent particles and are now being investigated by researchers as drug and gene delivery vehicles and blood substitutes. Current methods available for the preparation of microbubbles are insufficient as they result in microbubbles with a wide size distribution and as such filtration is necessary before their use. With a view to fill the above demand, a detailed investigation has been carried out in this research to learn the viability of co-axial electrohydrodynamic atomization (CEHDA) technique to prepare microbubbles. The research also focuses on the effects of the process parameters such as flow rates, applied voltage and material parameters such as electrical conductivity, surface tension and viscosity with the objective of preparing polymer or surfactant coated stabilized microbubbles with diameters < 8 μm and with a narrow size distribution. A model glycerol-air system was used so that the CEHDA technique was modified to generate suspensions of microbubbles to a diameter < 8 μm with a narrow size distribution and then to characterise the CEHDA microbubbling process in terms of size and stability with varying process parameters and material parameters. Construction of a parametric plot between the air flow rate and the liquid flow rate was extremely useful in identifying the flow rate regime of air and liquid or suspension or solution for the continuous microbubbling of the system used. With further investigations into the CEHDA microbubbling technique, it was possible to develop strategies, first, to prepare suspensions of stabilized phospholipids-coated microbubbles with a mean diameter of ~ 5 μm and a polydispersivity index of 9%, and second, polymeric microspheres with a mean diameter of 400 nm and a polydispersivity index of 8% using a biocompatible polymer

Bioinspired Design of Wetting and Anti-Wetting Surfaces via Thiol-ene Photopolymerization

Surface wettability is known to have a profound influence in both academic study and industrial application of materials. Superhydrophobic surfaces, with a static contact angle higher than 150° and a contact angle hysteresis lower than 10°, have received continued attention for their broad applications, such as self-cleaning, antifogging and frosting, and drag reduction. The continuous development of materials and approaches that used to create superhydrophobic surfaces has led to further exploration of coatings with other desirable properties such as superamphiphobicity, mechanical robustness and thermal stability. In this work, coatings with super wetting and super anti-wetting properties were designed and fabricated by tailoring the chemical composition and the morphology of the surface in an effort to expand the application and to improve the mechanical property of the coatings. In the first study, a superamphiphobic coating was prepared by spray deposition and followed up UV-polymerization of a hybrid organic-inorganic thiol-ene precursor. The combination of dual-scale roughness and low surface energy materials led to surfaces with strong water/ oil repellency and self-cleaning properties. In the second study, a superhydrophilic and superoleophobic membrane for oil/water separation applications was developed. The textured membrane morphology enhanced the hydrophilic and oleophobic properties of the surface. The efficiency of the superhydrophilic/superoleophobic membrane on oil/water separation was demonstrated by emulsion and dye contained emulsion separation studies. In the third study, a superhydrophobic surface was prepared with porogen leaching approach in an effort to reduce the loading level of NPs. The microphase separation and porogen leaching process resulted in microscale roughness. NPs migration from bulk to interphase led to the formation of nanoscale roughness. The combination of micro- and nano-scale feature provides the surface with superhydrophobicity with 50 wt.% reduced NPs loading level

Coating stent materials with polyhedral oligomeric silsesquioxane-poly(carbonateurea)urethane nanocomposites

The long-term efficacy of coronary or peripheral stenting is limited by in-stent restenosis (ISR), which occurs in 15 to 30% of patients and is attributed primarily to neointimal hyperplasia. By adding a drug-eluting coating, this rate has been reduced to about 5% or less. However, recently longer-term follow-up data has highlighted problems with drug-coated stents, including late stage thrombosis. A bio-stable poly(carbonate-urea)urethane has been used for stent coating and the surface properties of the polymer have been optimised by incorporating the polyhedral oligomeric silsesquioxane molecule. These POSS polymers improve the adhesion and the growth of endothelial cells. The work described in this thesis, presents an innovative approach in self-expanding/balloon expandable coronary stent design that incorporates a NiTi/stainless steel alloy scaffold with a polyhedral oligomeric silsesquioxane- poly (carbonate-urea) urethane nanocomposite polymer (POSS-PCU) coating. Electrohydrodynamic spraying and ultrasonic atomization spraying of the non-biodegradable nanocomposite polyhedral oligomeric silsesquioxane (POSS) polymer have been investigated in detail for coating metallic stent materials and compared with dip coating. Because of the tight geometry of coronary stents, these new coating techniques have been shown to offer advantages over traditional coating techniques. These advantages include, reduced polymer consumption, precise coating thickness as low as 10 μm and a highly controllable spray which leads to consistent reproducible results. However, poor adhesion, or bond deterioration over the lifespan/ deployment of the device could reduces the efficiency and could impart even more complexity to the implant including formation of debris which can induce thrombus formation. Changing the surface physical property/chemical composition through the proposed protocol has been shown to increase the bonding strength by up to three times. This study has identified a new process and conditions which can be used in stent coating research

An investigation into the use of flow-focusing atomization with spray drying for the production of narrow particle size distributions

The droplet size distribution produced by the atomization system within a spray d1yer is vital in defining the output particle size distribution, which in turn can strongly influence the subsequent flow, dissolution, ingestion or bioavailability of the final product. This thesis explores the capability of a simple atomizing system for the production of narrow droplet size distributions within an industrially-relevant spray dryer. The combination of constrained droplet size distribution, defined solute concentration and selected processing conditions has been evaluated to determine the influence upon the physicochemical properties of a model active pharmaceutical ingredient, and the dosing characteristics of formulated products. The flow focusing atomizer was demonstrated to be capable of generating distinct droplet size distributions, and able to produce similar performance in the dynamic environment within a spray dryer. Experiments conducted using the inhaled corticosteroid mometasone furoate indicate that droplet size, concentration and drying conditions are important in determining the particle size, texture and thermodynamic properties of the output powder. Analysis of formulations containing the flow-focused mometasone furoate particles defined a clear link between the impaction profile in a cascade impactor and droplet size and spray d1ying conditions

Experimental and computational analysis of bubble generation combining oscillating fields and microfluidics

Microbubbles generated by microfluidic techniques have gained substantial interest in various fields such as food engineering, biosensors and the biomedical field. Recently, T-Junction geometries have been utilised for this purpose due to the exquisite control they offer over the processing parameters. However, this only relies on pressure driven flows; therefore bubble size reduction is limited, especially for very viscous solutions. The idea of combining microfluidics with electrohydrodynamics has recently been investigated using DC fields, however corona discharge was recorded at very high voltages with detrimental effects on the bubble size and stability. In order to overcome the aforementioned limitation, a novel set-up to superimpose an AC oscillation on a DC field is presented in this work with the aim of introducing additional parameters such as frequency, AC voltage and waveform type to further control bubble size, capitalising on well documented bubble resonance phenomena and properties. Firstly, the effect of applied AC voltage magnitude and the applied frequency were investigated. This was followed by investigating the effect of the mixing region and electric field strength on the microbubble diameter. A capillary embedded T-junction microfluidic device fitted with a stainless steel capillary was utilised for microbubble formation. A numerical model of the T-Junction was developed using a computational fluid dynamics-based multiphysics technique, combining the solution of transport equations for mass and momentum (Navier-Stokes Equations), a Volume of Fluid algorithm for tracking the gas-liquid interfaces, and a Maxwell Equations solver, all in a coupled manner. Simulation results were attained for the formation of the microbubbles with particular focus on the flow fields along the detachment of the emerging bubble. Experimental results indicated that frequencies between 2-10 kHz have a pronounced effect on the bubble size, whereas elevated AC voltages of 3-4 〖kV〗_(P-P) promoted bubble elongation and growth. It was observed that reducing the mixing region gap to 100 μm facilitated the formation of smaller bubbles due to the reduction of surface area, which increases the shear stresses experienced at the junction. Reducing the tip-to-collector distance causes a further reduction in the bubble size due to an increase in the electric field strength. Computational simulations suggest that there is a uniform velocity field distribution along the bubble upon application of a superimposed field. Microbubble detachment is facilitated by the recirculation of the dispersed phase. A decrease in velocity was observed upstream as the gas column occupies the junction suggesting the build-up in pressure, which corresponds to the widely reported ‘squeezing regime’ before the emerging bubble breaks off from the main stream. The novel set-up described in this work provides a viable processing methodology for preparing microbubbles that offers superior control and precision. In conjunction with optimised processing parameters, microbubbles of specific sizes can be generated to suit specific industrial applications