Yes / Thermal ink-jet printing (TIJP) is shown to be a rapid (minutes) method with which to prepare pharmaceutical co-crystals; co-crystals were identified in all cases where the co-formers could be dissolved in water and/or water/ethanol solutions.

During the operation of phase-change ink-jet printers a bubble formation phenomenon often occurs. These bubbles are detrimental to the operation of the printer and substantial efforts are made to remove them. The objective of this research was 1: to develop a fundamental understanding of how bubble or void formation occurs during the phase-change process, and, 2: to develop a simple computer model to simulate this behavior which can then be used as a tool for better design of print-head geometries. Preliminary experimental work indicated the void formation to be a result of the density change accompanying the phase-change process. The commercial numerical code, Flow 3-D, was used to model the phase-change process in print-head geometries and substantiate certain simplifying assumptions. These assumptions included the effect of convection on the process and the effect of the varying material properties. For channel sizes less than 0.5 cm the phase-change process was found to be a pure conduction process. Convection effects are thus negligible and can be eliminated from the model. The variability of density, specific heat and thermal conductivity must be included in the model, as they affect the phase-change process dramatically. Specific heat is the most influential of the properties and determines, along with the conductivity, the rate at which the phase change takes place. The density must be included since it is directly linked to the void formation. / Graduation date: 1994

An imaging system was developed to visualize Drop-on-Demand (DOD) inkjet drop formation and impaction on substrate over drop sizes and impaction speeds of the magnitudes encountered in applications of inkjet printing. Using a pulsed laser, a low-speed charge-coupled-device (CCD) camera, and signal generators, the imaging system based on flash photography was used to capture sharp images with a temporal resolution of 200 ns and a spatial resolution of 0.81 micron/pixel. First, the dynamics of DOD drop formation was studied experimentally. The effects of the driving signal, which controls the piezoelectric transducer that produces the pressure pulse to drive the liquid from the reservoir through the orifice, have been examined along with those of liquid properties. The main stages of DOD drop formation, including ejection and stretching of liquid, pinch-off of liquid thread from the nozzle exit, contraction of liquid thread, breakup of liquid thread into primary drop and satellites, and recombination of primary drop and satellites, are analyzed. A necessary condition for the recombination of the primary drop and satellite and the limit for liquid thread length without breakup during contraction are proposed. Second, using the visualization system coupled with a motorized stage, micron-drop impaction on a smooth substrate was investigated over a regime of We and Oh typical for inkjet printing applications. The results indicate that scaling of micron-drop impaction from millimeter-drop impaction, based on dimensionless numbers (Oh, We and cos ), is valid. The predictions of maximum spreading ratio by six existing models agree well with experimental values for high-We impaction, but not for low-We and low-contact-angle impactions; however, the model of Park et al. predicts well for high- and low-We impaction due to its inclusion of spontaneous spreading dissipation. Fingering and splashing do not occur in the micron drop impaction on either dry solid substrates or a pre-existing liquid layer. The drying time of a micron drop deposited on a substrate is less than one second and increases as the contact angle of the drop on the substrate increases.

A series of novel metallic nanoparticle and suspension were developed and synthesized for ink-jet printing and spin coating applications. Organic components, such as alkanethiols and amines, were used as new capping agent design. The suspension was characterized by NMR, ESCA, TEM, SEM, EDS, TGA, DTG, DSC, TA-MS for chemical composition and three-dimension SAMs desorption.

The research discussed in this dissertation was conducted to understand drop formation of inkjet printing with inks containing polymer. Solutions containing a water soluble polymer, poly ethylene oxide (PEO), with different molecular weights and polydispersities were used as inks. A flash photographic technique was used to visualize the whole process of DOD drop formation of dilute polymer solutions. The effects of driving signal, frequency and liquid properties on drop speed, drop size, breakup time and the formation of satellites were studied in detail. The addition of PEO increases the shear viscosity at all molecular weights, but the change is small for dilute solutions. However, the addition of a small amount of PEO can have a significant effect on the DOD drop formation process, increasing breakup time, decreasing primary drop speed and decreasing the number of satellites in some cases. The effects depend on both molecular weight and concentration. At lower molecular weights (14k and 35k g/mol), the effect of PEO was small when the drop formation process for the dilute solution was compared with that of a Newtonian liquid having similar shear viscosity, and the effect of PEO was small even at concentrations large enough that the solution does not fall in the dilute regime. As molecular weight is increased, the effects of PEO on DOD drop formation increase significantly, and the effects of concentration become important. These effects are explained by the fluid elasticity which increases with increasing in molecular weight and concentration. When the liquid jets out of the nozzle, the polymer chains are stretched, and thus depart from their ideal coiled state. As a result, an elastic stress develops in the liquid column and resists capillarity-driven pinch off from the nozzle and is responsible for the decrease in drop speed and longer breakup time. DOD drop formation data were shown to correlate closely with effective relaxation time, proposed by Tirtaatmadja based on Rouse-Zimm theory. When driving voltage amplitude is 44.2 V, two important parameters (breakup time and primary drop speed) in DOD drop formation for solutions containing monodispersed PEO and aqueous solutions containing mixtures of monodispersed PEO were closely predicted by correlation equations involving effective relaxation time . A mixture rule was developed to calculate the relaxation time for mixtures of monodispersed PEO. However, for polydispersed PEO, effective relaxation time was based on viscous molecular weight since the molecular weight distributions of the polydispersed PEO were unknown. When breakup time was plotted versus effective relaxation time for 1000k g/mol PEO, the data did not lie on the same line as that for the 100k and 300k g/mol PEO. This is believed to be due to the molecular weight distributions of the polydispersed PEO. When more than one species are present, viscous average molecular weight does not adequately account for the long chain species making up the polymer sample. DOD drop formation dynamics is highly affected by the actuating waveform, including the driving voltage, waveform shape, and frequency. The effects of parameters (jetting frequency, voltage amplitude and the shape of waveform) characterizing the signal were investigated. The open time and first drop problem were also studied. Research in this dissertation gives a better understanding of DOD drop formation process of polymer solutions, which may lead to improvement of inkjet printing quality for a variety of industry inks and polymer micro scale deposition and patterning in large areas.

Ink-jet deposition is an emerging technology that provides a more efficient, economic, scalable method of manufacturing than other traditional additive techniques by laying down droplets layer by layer to build up 3-D objects. The focus of this thesis is to investigate the material interface evolution during the droplet deposition process, which holds the key to understanding the material joining process. Droplet deposition is a complicated process and can be broken down into droplet impingement dynamics and droplet hardening. This research focuses on the study of the interface dynamics of droplet impingement. In order to study the interface dynamics, a novel metric is developed to quantify the evolving geometry of the droplet interface in both 2-D and 3-D for single and multiple droplets respectively, by measuring the similarity between the evolving droplet geometry and a desired shape. With the developed shape metric, the underlying physics of the interface evolution for single droplet impingement are examined with simulations using an experimentally validated numerical model. Results show that the Weber number determines the best achievable shape and its timing during the droplet impingement when Ohnesorge number is smaller than 1, while the Reynolds number is the determining factor when Ohnesorge number is larger than 1. A regime map is constructed with the results and an empirical splash criterion to guide the choice of process parameters for given fluid properties in order to achieve the best shape without splash for single droplet impingement. In order to study the interface dynamics for multiple droplet interaction, which is computationally prohibitive for commercial software packages, an efficient numerical model is developed based on the Lattice Boltzmann (LB) method. A new LB formulation equivalent to the phase-field model is developed with consistent boundary conditions through a multiscale analysis. The numerical model is validated by comparing its simulation results with that of commercial software COMSOL and experimental data. Results show our LB model not only has significant improvement of computational speed over COMSOL but is also more accurate. Finally, the developed numerical solver is used to study the interface evolution of multiple droplet interaction with the aid of the 3-D shape metric proposed before. Simulations are performed on a wide range of impingement conditions for two-droplet, a-line-of-droplet, and an-array-of-droplet interactions. The underlying physics of the interface coalescence and breakup coupling with the impingement dynamics are examined. For line-droplet interaction, the strategy for achieving the equilibrium shape in the shortest time is studied. An important issue is discovered for array-droplet interaction, which is the air bubble formation during the droplet interaction. The mechanism for the air bubble formation is investigated and the strategy to avoid this undesirable effect is also suggested. This thesis has largely reduced the gap between basic science of studying droplet impingement dynamics and engineering application in inkjet deposition and provided preliminary insights on the material joining process for additive manufacturing.

The objective of the proposed research is to integrate nanotechnology, applied electromagnetics, and inkjet printing fabrication methods to develop a series of novel inkjet-printed RF modules for sensing and communication applications: wireless gas sensor, wearable RFID tag, and RF inductor. Passive, wireless sensors have various applications in a wide range of fields including military, industry, and medicine. However, there are issues such as cost, sensitivity of sensors, manufacturing complexities, and feasibility of further miniaturization of these RF modules. One aspect of this research investigates the feasibility of addressing these issues by integrating nanotechnology and applied electromagnetics. The underlying common theme for the three designs is inkjet-printing silver nanoparticles on organic paper substrate. The research will investigate the characterization of thin film carbon nanotubes and the optimization of inkjet-printing the CNT material on paper substrate followed by the design of a patch antenna based gas sensor. Measurement results from a closed measurement system will be shown. Secondly, an inkjet-printed, conformal, wearable RFID tag on an artificial magnetic conductor is designed and tested using an RFID Reader. Lastly an inkjet-printed high Q RF inductor is designed and integrated with magnetic nanomaterial to evaluate the feasibility of increasing inductance using high permeability nanomaterial. Through the design and testing of the aforementioned three designs, it will be shown that through a multidisciplinary design process, novel, low-cost RF modules can be designed for sensing and communication applications.

The effect of fabric structure and yarn-to-yarn liquid migration on the overall liquid transport behavior of fabrics is investigated in this research. Sorption of liquid from an unlimited reservoir as well as sorption of a limited quantity of liquid by fabrics representing different structural parameters is studied in detail. Sorption of a limited quantity of liquid is studied by performing drop spreading experiments on fabrics. The spreading and wicking of micron sized drops which are deposited on textile fabrics during ink jet printing is also studied. How the fabric structure related variables influence the spreading of ink drops and how exactly spreading influences printing quality is investigated in this research. Results showed that the wicking in fabrics is determined by the wicking rates of the yarns, thread spacing and more importantly by the rate at which liquid migrates from longitudinal to transverse threads and again from transverse threads back to longitudinal threads. Drop spreading rates were also determined by fabric structure. In general, compact and thinner fabrics showed highest drop spreading rates. Drop spreading rates are primarily affected by the manner and the rate at which liquid migrates from yarn to yarn. Analysis of the results of ink jet printing of pigment ink on textile fabrics showed that excessive drop spreading and higher line widths were observed where continuous and narrow capillaries prevail on the surface of yarns. Yarn surface characteristics are more important than fabric construction parameters.

Thesis (M.S.)--State University of New York at Binghamton, Thomas J. Watson School of Engineering and Applied Science, Department of Mechanical Engineering, 2009. / Includes bibliographical references.

Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Dr. Manos Tentzeris; Committee Member: Dr. Gregory Durgin; Committee Member: Dr. Joy Laskar.