104 research outputs found

    Fluid characterisation and drop impact in inkjet printing for organic semiconductor devices

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    An inkjet printer can deposit a very small volume of liquid with high positional accuracy, high speed and low cost. As a maskless, non-contact additive patterning method, inkjet printing technology is increasingly being explored as an alternative to lithography, etching and vapour deposition processes to pattern electrical conductors and thin films with applications in printed electronic devices. The functional inks used in many of the applications involve non-linear viscoelasticity and their behaviours in the context of inkjet printing have not been fully understood. This thesis aims to characterise Newtonian and non-Newtonian properties of inkjet fluids and identify the key parameters affecting drop impact and spreading processes. Various fluid characterisation techniques such as the filament stretching rheometer and piezoelectric axial vibrator are explored. We propose an experimental method to assess the jettability of non-Newtonian inkjet fluids, without using an inkjet print head. The oblique collision of two continuous liquid jets leads to the formation of a thin oval liquid sheet bounded by a thicker rim which disintegrates into ligaments and droplets. Under certain conditions the flow structure exhibits a remarkably symmetrical “fishbone” pattern composed of a regular succession of longitudinal ligaments and droplets. Good correlation was found between the maximum included angle of the fishbone pattern and the maximum ligament length in the jetting experiments, which suggests that a test based on oblique impinging jets may be useful in the development of fluids for ink jet printing. High-speed imaging is used to analyse the impact and spreading of sub-30 μm drops of diethyl phthalate or polystyrene solutions in diethyl phthalate on to smooth glass surfaces with controlled wettability at speeds from 3 to 8 m s-1, under conditions representative of drop-on-demand inkjet printing. Data on drop height and spreading diameter are generated with high time and spatial resolution, over eight orders of magnitude in timescale. The effects of fluid viscosity and elasticity, which significantly affect jetting performance, are negligible throughout the whole deposition process, with no significant difference between spreading curves. The values of the fluid surface tension and the substrate wettability also have no effect on the kinematic, spreading or relaxation phases, but a marked influence on the wetting phase, in terms of the speed of expansion of the contact diameter and the final spreading factor

    Laser-induced forward transfer (LIFT) of water soluble polyvinyl alcohol (PVA) polymers for use as support material for 3D-printed structures

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    The additive microfabrication method of laser-induced forward transfer (LIFT) permits the creation of functional microstructures with feature sizes down to below a micrometre [1]. Compared to other additive manufacturing techniques, LIFT can be used to deposit a broad range of materials in a contactless fashion. LIFT features the possibility of building out of plane features, but is currently limited to 2D or 2½D structures [2–4]. That is because printing of 3D structures requires sophisticated printing strategies, such as mechanical support structures and post-processing, as the material to be printed is in the liquid phase. Therefore, we propose the use of water-soluble materials as a support (and sacrificial) material, which can be easily removed after printing, by submerging the printed structure in water, without exposing the sample to more aggressive solvents or sintering treatments. Here, we present studies on LIFT printing of polyvinyl alcohol (PVA) polymer thin films via a picosecond pulsed laser source. Glass carriers are coated with a solution of PVA (donor) and brought into proximity to a receiver substrate (glass, silicon) once dried. Focussing of a laser pulse with a beam radius of 2 µm at the interface of carrier and donor leads to the ejection of a small volume of PVA that is being deposited on a receiver substrate. The effect of laser pulse fluence , donor film thickness and receiver material on the morphology (shape and size) of the deposits are studied. Adhesion of the deposits on the receiver is verified via deposition on various receiver materials and via a tape test. The solubility of PVA after laser irradiation is confirmed via dissolution in de-ionised water. In our study, the feasibility of the concept of printing PVA with the help of LIFT is demonstrated. The transfer process maintains the ability of water solubility of the deposits allowing the use as support material in LIFT printing of complex 3D structures. Future studies will investigate the compatibility (i.e. adhesion) of PVA with relevant donor materials, such as metals and functional polymers. References: [1] A. Piqué and P. Serra (2018) Laser Printing of Functional Materials. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA. [2] R. C. Y. Auyeung, H. Kim, A. J. Birnbaum, M. Zalalutdinov, S. A. Mathews, and A. Piqué (2009) Laser decal transfer of freestanding microcantilevers and microbridges, Appl. Phys. A, vol. 97, no. 3, pp. 513–519. [3] C. W. Visser, R. Pohl, C. Sun, G.-W. Römer, B. Huis in ‘t Veld, and D. Lohse (2015) Toward 3D Printing of Pure Metals by Laser-Induced Forward Transfer, Adv. Mater., vol. 27, no. 27, pp. 4087–4092. [4] J. Luo et al. (2017) Printing Functional 3D Microdevices by Laser-Induced Forward Transfer, Small, vol. 13, no. 9, p. 1602553

    Proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress

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    Published proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress, hosted by York University, 27-30 May 2018

    NASA Tech Briefs, September 2011

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    Topics covered include: Fused Reality for Enhanced Flight Test Capabilities; Thermography to Inspect Insulation of Large Cryogenic Tanks; Crush Test Abuse Stand; Test Generator for MATLAB Simulations; Dynamic Monitoring of Cleanroom Fallout Using an Air Particle Counter; Enhancement to Non-Contacting Stress Measurement of Blade Vibration Frequency; Positively Verifying Mating of Previously Unverifiable Flight Connectors; Radiation-Tolerant Intelligent Memory Stack - RTIMS; Ultra-Low-Dropout Linear Regulator; Excitation of a Parallel Plate Waveguide by an Array of Rectangular Waveguides; FPGA for Power Control of MSL Avionics; UAVSAR Active Electronically Scanned Array; Lockout/Tagout (LOTO) Simulator; Silicon Carbide Mounts for Fabry-Perot Interferometers; Measuring the In-Process Figure, Final Prescription, and System Alignment of Large; Optics and Segmented Mirrors Using Lidar Metrology; Fiber-Reinforced Reactive Nano-Epoxy Composites; Polymerization Initiated at the Sidewalls of Carbon Nanotubes; Metal-Matrix/Hollow-Ceramic-Sphere Composites; Piezoelectrically Enhanced Photocathodes; Iridium-Doped Ruthenium Oxide Catalyst for Oxygen Evolution; Improved Mo-Re VPS Alloys for High-Temperature Uses; Data Service Provider Cost Estimation Tool; Hybrid Power Management-Based Vehicle Architecture; Force Limit System; Levitated Duct Fan (LDF) Aircraft Auxiliary Generator; Compact, Two-Sided Structural Cold Plate Configuration; AN Fitting Reconditioning Tool; Active Response Gravity Offload System; Method and Apparatus for Forming Nanodroplets; Rapid Detection of the Varicella Zoster Virus in Saliva; Improved Devices for Collecting Sweat for Chemical Analysis; Phase-Controlled Magnetic Mirror for Wavefront Correction; and Frame-Transfer Gating Raman Spectroscopy for Time-Resolved Multiscalar Combustion Diagnostics

    Droplet impact and contact angle dynamics: From spreading and splashing to 3D printing.

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    PhD ThesisUnderstanding the contact line dynamics during droplet impact is critically important for industrial processes such as coating, the spraying of pesticides and for the design of anti-icing surfaces or impermeable clothing. It is known that, upon impacting on a solid, a droplet can spread, bounce off the substrate or splash depending on the liquid characteristics, the solid properties, the impact speed and the ambient pressure. In this thesis, we explore droplet impact in terms of some of these variables. Consequently, this work is focused on the experimental study of the contact line dynamics of impacting droplets on substrates ranging from wettable to non-wettable and from porous to non-porous. In particular, we focus on the parameters affecting: i) the splashing threshold of impacting droplets on solid substrates and ii) the penetration of impacting droplets through textiles. Furthermore, we apply our findings to the development of a liquid latex droplet-on-demand printing system. Most of the experiments in this thesis consist of the visualisation, by high speed imaging, of the impact of ethanol, water and aqueous glycerol droplets on solid and textile substrates. In addition, we present a custom-made Matlab algorithm that uses a polynomial fitting approach to extract the dynamic contact angle as a function of the contact line velocity. Moreover, we analyse the effect of droplet shape, the order of the fitting polynomial and the fitting domain, on the measurement of the contact angle on various stages following droplet impact. We use our experimental setup to demonstrate the importance of wettability and substrate roughness on the contact line dynamics and the impacting outcome. For smooth surfaces, we show that the maximum advancing contact angle ( max) is greater than 87 degrees for all the liquid/substrates. Moreover, we show that splashing depends on the substrate wettability and its threshold can be parameterised by max and the splashing ratio. Correspondingly, for rough surfaces, we determine that max increases with increasing substrate roughness. Furthermore, we establish that the ratio of the peak to peak roughness to the surface feature mean width, in conjunction with max and the splashing ratio, adequately predict the splashing threshold. Similarly, for the droplet impact dynamics on textiles, we find that the textile characteristics, such as the pore size and solid fraction, are critical for the impact outcome. Correspondingly, we find three different impact regimes, namely, ‘no penetration’, ‘capture’ and ‘complete penetration’. Additionally, by balancing the kinematic pressure with the capillary pressure, we find a critical pore size for the transition from capture to complete droplet penetration in terms of the Weber number. Finally, we present a setup that permits the printing, by droplet impact, of liquid latex on paper with a high solid content (60 wt %). The process is controllable and reliable, making the printing of patterns possible. With this setup, multilayer objects were created from pure liquid latex, as well as from micronized rubber powder and latex suspensions. These results demonstrate the potential of droplet-based additive manufacturing processes to produce prints of liquid latex and tire rubber reuse

    Microfluidics and Nanofluidics Handbook

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    The Microfluidics and Nanofluidics Handbook: Two-Volume Set comprehensively captures the cross-disciplinary breadth of the fields of micro- and nanofluidics, which encompass the biological sciences, chemistry, physics and engineering applications. To fill the knowledge gap between engineering and the basic sciences, the editors pulled together key individuals, well known in their respective areas, to author chapters that help graduate students, scientists, and practicing engineers understand the overall area of microfluidics and nanofluidics. Topics covered include Finite Volume Method for Numerical Simulation Lattice Boltzmann Method and Its Applications in Microfluidics Microparticle and Nanoparticle Manipulation Methane Solubility Enhancement in Water Confined to Nanoscale Pores Volume Two: Fabrication, Implementation, and Applications focuses on topics related to experimental and numerical methods. It also covers fabrication and applications in a variety of areas, from aerospace to biological systems. Reflecting the inherent nature of microfluidics and nanofluidics, the book includes as much interdisciplinary knowledge as possible. It provides the fundamental science background for newcomers and advanced techniques and concepts for experienced researchers and professionals

    NASA Propulsion Engineering Research Center, Volume 2

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    This is the second volume in the 1994 annual report for the NASA Propulsion Engineering Research Center's Sixth Annual Symposium. This conference covered: (1) Combustors and Nozzles; (2) Turbomachinery Aero- and Hydro-dynamics; (3) On-board Propulsion systems; (4) Advanced Propulsion Applications; (5) Vaporization and Combustion; (6) Heat Transfer and Fluid Mechanics; and (7) Atomization and Sprays

    Jetting of multiple functional materials by additive manufacturing

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    The rise and consolidation of Additive Manufacturing (AM) as a technology has made possible the fabrication of highly customised and complex products in almost every industry. This not only allows the creation of objects that were impossible just a few decades ago but also facilitates the production of small runs of products at a reasonable cost, which reduces the design-prototyping cycles and boosts product innovation. However, to produce truly functional parts it is desirable for these systems to be able to deposit multiple complex materials in a single process to locally embed controllable properties such as electrical conductivity or sensing capabilities into the produced geometries. Consequently, a review of current AM technologies capable of depositing conductive materials is performed in this PhD and discussed to find the most suitable approaches. Similarly, existing multi-material set-ups are studied to find limitations and common practices to create a system that is capable of fulfilling the objectives of this work. Piezo-activated inkjet printing (PIJ) is identified as an appropriate technology for multi-material applications due to its non-contact nature, high spatial resolution, capability of mixing and digitally grading materials and simple scale-up of the process. Furthermore, in the last decade it has been shown that jetting can be used for the accurate deposition of a wide range of functional materials. However, upon detailed review of this method, the limitations that it imposes on the compositions of the inks are identified as its main drawback. Specifically, the solid content and molecular weight of the fluids that can be jetted are restricted by the viscosity of the final ink, typically under 40 mPa·s. This is problematic in the case of jetting conductive materials, since it forces the solid content to be very low, therefore yielding very thin and often inhomogeneous layers. Additionally, all the organic components on the inks added to facilitate its ejection need to be removed, which typically means longer and more aggressive post-processes before rendering the printed tracks conductive. For this reason, drop-on-demand micro-dispensing valves were chosen as a high viscosity jetting (HVJ) approach in this work, with the intention of assessing their capability as a suitable tool for multi-material AM of functional inks. However, since their resolution and speed are lower than conventional inkjet, a hybrid approach is presented including micro-dispensing valves and inkjet printheads capable of depositing a wide range of viscosities in a single process. A comprehensive description of the hybrid set-up is given, discussing its main elements including the printing heads, the custom design printer assembly, the ultraviolet (UV) and infrared (IR) lamps installed for in-situ processing, the monitoring system and the set-up to measure the evolution of the electrical resistance in printed tracks in real time during post-processing. Additionally, the printing strategy and process flow is discussed. The investigated set-up was used to study the printability and performance of several functional materials ranging from UV-curable polymers to conductive formulations such as carbon paint, a silver nanoparticle-based paste and a dispersion of PEDOT:PSS. Each material was thoroughly characterised prior to printing with a special focus on viscosity. Their drop formation and deposition processes were studied at different printing settings using high speed imaging and footprint analysis of the deposited drops. These tests were used to obtain sets of working parameters that allow reliable printing and were used to produce 2D patterns with different resolutions to find the drop spacing that results in flat homogeneous films. Later, these films were post-treated according to the requirements of each material and multilayer structures were produced and analysed with an optical profilometer. The cross-section of these 3D tracks was used together with the measured resistance to obtain the electric conductivity of the materials under the printing conditions used. Finally, the accumulated information during the previous stages of printing was used to produce 3D multi-material demonstrators with incorporated conductive tracks, electric components and electroluminescent elements. These proof-of-concept samples were used to discuss limitations of the approach and showcase future possibilities of the system

    Bibliography of Lewis Research Center Technical Publications announced in 1991

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    This compilation of abstracts describes and indexes the technical reporting that resulted from the scientific engineering work performed and managed by the Lewis Research Center in 1991. All the publications were announced in the 1991 issues of STAR (Scientific and Technical Aerospace Reports) and/or IAA (International Aerospace Abstracts). Included are research reports, journal articles, conference presentations, patents and patent applications, and theses
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