Inkjet printing technology has been developing rapidly during recent years, pressing the ink and paper manufacturers to develop a better understanding of the mechanism of fixation of inkjet dye into the substrate. The aim of the work described in this thesis was to investigate the three-dimensional distribution of inkjet dye in paper and the interaction between dye and paper using advanced fluorescence microscopy techniques, Confocal Laser Scanning Microscopy (CLSM), and Two-photon Fluorescence Lifetime Imaging Microscopy (2P-FLIM). It has been shown that CLSM is a valuable, non-destructive, rapid technique for threedimensional imaging of printed samples and evaluation of print quality. The intrinsic fluorescence of both the inkjet dye and the paper substrate can be used to determine the spread and penetration of ink droplets in different inkjet papers. The optical sectioning capability of CLSM enables the position of the ink layer relative to the paper surface and the penetration depth of the ink to be quantified. It was observed that while in the microporous type of inkjet paper the penetration depends on the quantity of ink in the printed sample, in the swellable type of inkjet paper the penetration is almost the same for different amounts of ink. 2P-FLIM has been employed to spatially map, in three-dimensions, fluorescence lifetimes by measuring the lifetime at each pixel in the image. Fluorescent molecules in both the ink and paper were analysed. Because the fluorescence lifetime is affected by the local molecular environment, the fluorescence lifetime maps provide information on the interaction between inkjet dye and paper. Analysis of fluorescence lifetime maps reveals the interaction between dye molecules and silica or alumina particles in the paper, variations of the molecular environment within a single ink dot and that interaction between dye and paper is affected by pH.

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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.

Continuous InkJet (CIJ) printing is a common 2-Dimensional printing technique that creates jets of ink that breakup into drops as they are propelled towards a substrate to create a print. Inkjet printing has been used not only to print on paper, but to manufacture a variety of devices including OLEDs, solar cells and microfluidic devices. In many cases, the ‘ink’ consists of a polymer dissolved in a volatile solvent. As this ink is sprayed on to the substrate, the solvent evaporates, leaving the polymer behind as the print. The addition of the polymer alters the physics of the problem significantly enough that it varies greatly from jetting only a fluid with nothing dissolved in it. Polymers impart viscoelasticity to the solution, creating ink jets that are long-lived and difficult to break into droplets. In order to maintain the formation of drops in a repeatable, uniform fashion, a disturbance of known magnitude is imposed upon the jet. While jetting a liquid with no additives in it, this disturbance governed jet breakup leads to the formation of satellite drops, smaller drops of fluid in-between the main jet drops. Satellite drops are an undesirable occurrence in inkjet printing because of their unpredictable behavior and potential to affect the quality of the print. However, the addition of polymers to the liquid can control and potentially suppress the formation of these satellite drops, greatly improving the print quality. The elasticity of iv the polymer and its ability to influence the jet behavior and formation of satellite drops is highly dependent on multiple factors including the backbone rigidity, molecular weight and the concentration in which it is present in the fluid. Strongly viscoelastic effects have a marked effect on the jet and their presence can be quantified quite easily. However, some polymers show weak viscoelastic behavior while present in the ink fluids and may or may not affect the jetting process. The objective of this study is to examine such a class of polymeric fluids that are weakly viscoelastic in the context of inkjet printing and satellite drop formation. Firstly, the fluids are tested in an extensional rheology setup called Capillary Breakup Extensional Rheometry – Drop-on-Substrate (CaBER-DoS) to quantify their extensional properties. Then, they are tested in an emulated inkjet printing setup. The goal is to quantify the impact of the aforementioned factors on jetting and using satellite drop behavior as a guiding metric to understanding viscoelastic behavior in inkjet printing fluids.

In-vitro electronic devices are promising to dynamically monitor minute-changes in biological systems. Electronic devices based on conducting polymers such as poly(3,4- ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) provide suitable and attractive substrates for biointerfacing. The soft polymer surface acts as a cushion for the living systems to interface while electronically detecting their properties. However, to this date, most bioelectronics devices have been fabricated via multi-step lithography techniques, which do not allow for mass fabrication and hence high throughput biosensing. Inkjet printing presents an alternative to fabricate organic bioelectronic devices. Besides being low-cost, inkjet printing allows to fabricate several devices in a short time with flexible design patterns and minimal material waste. Here, using inkjet printing, we fabricated PEDOT:PSS based organic electrochemical transistors (OECTs) for biomembrane interfacing. We optimized the deposition of various inks (silver nanoparticles (AgNPs), PEDOT:PSS, and the dielectric SU-8) used during the fabrication of these devices. We characterized the electrical characteristics of all-printed OECTs with various geometries and identified the high-performing ones. Due to the flexibility of ink optimization and design patterns, these all inkjet-printed electronic devices provide an alternative for mass production of biointerfacing platforms.

The stability of inkjet print is influenced by a lot of factors. Just the surrounding environment in image stability plays an important role. When the prints fade, not only this does occur by light exposure, but also considerable effect has relative humidity, ozone and other air pollutants. The types of receiving layers or ink composition belong to other factors, which affect the stability of prints. This diploma thesis deals with the long-term ageing of digital prints produced by ink jet technology. The study of resistance of inkjet prints was realized on nine different types of media. Samples were prepared with use of dye-based and pigment-based inks. The attention was especially focused on the influence of light on print durability, but study was also oriented on the impact of ozone. The samples were exposed to the indoor daylight. Changes in printed colours were measured and evaluated in colorimetric quantities. In this study of inkjet prints degradation the dependence of colour gamut volumes on UV and VIS exposure dose was evaluated.

Wearables for health monitoring are rapidly advancing as evidenced by the number of wearable products on the market. More recently, the US Food and Drug Administration approved the Apple Watch for heart monitoring, indicating that wearables are going to be a part of our lives sooner than expected. However, wearables are still based on rigid, conventional electronic materials and fabrication procedures. The use of flexible conducting materials fabricated on flexible substrates allows for more comprehensive health monitoring because of the seamless integration and conformability of such devices with the human skin. Many materials can be used to fabricate flexible electronics such as thin metals, liquid metals, conducting polymers, and 1D and 2D materials. Ti3C2 MXene is a promising 2D material that shows flexibility as well as desirable electronic properties. Ti3C2 MXene is easily processable in aqueous solutions and can be an excellent functional ink for inkjet printing. Here we report the fabrication and the properties of Ti3C2 MXene films inkjet-printed from aqueous dispersions with a nonionic surfactant. The films are uniform and formed with only a few layers on glass and tattoo paper. The MXene films printed on tattoo are used to record ECG signals with comparable signal-to-noise ratio to commercial Ag/AgCl electrodes despite the absence of gels to lower skin-contact impedance. Due to their high charge storage capacity and mixed (ionic and electronic) conductivity, inkjet-printed MXene films open up a new avenue for applications beyond health monitoring.

<div>With an eye towards applications such as the selective sensing of volatile organic compounds (VOCs) or micro-scale thrust generation, inkjet printing was explored as a means to selectively deposit functional materials. The work detailed herein explores a series of fundamental steps to gain expertise related to the piezoelectric inkjet printing of functional materials. The successful printing of nanothermite was demonstrated with two unique printing techniques. Furthermore, the integration of this material with an ignition mechanism was shown to create a fully printed igniter energetic system. These advancements support future work related to the printing of other energetic materials necessary to create tunable reactive systems. This knowledge was then translated into the development of resonant mass sensing devices that are selectively functionalized using inkjet printing. This approach to functionalization allowed for the precise deposition of receptive chemistries on devices resulting in selective, highly-sensitive devices that successfully detected biomarkers secreted after traumatic brain injuries and harmful VOCs. This work implemented oscillator-based sensors to achieve a low-cost, low-power sensor platform with redundant elements. Furthermore, the predictive capabilities of these devices were explored using least squares and linear regression modeling.</div>

Manufactured products, such as furniture, laminate flooring, and large signs, are very labour intensive, time-consuming, and costly to produce as they require multiple coating and cutting operations on a series of independent machines, which can each introduce manufacturing errors between the tools and the work piece. By combining the processes of printing and milling, printing integrated manufacturing has the potential to eliminate some of these steps, significantly reduce errors, and preserve resources. Inkjet printing is an ideal method for both image transfer and coating operations due to its non-contact method of directly depositing various types of fluid onto a substrate. With improved positioning accuracy and droplet miniaturisation, inkjet printing could even be used for future applications like the mass-production of MEMS devices, which are traditionally fabricated with a highly complex process involving photolithography. This thesis presents the integration of a Xaar 126 inkjet printing system with an existing industrial flatbed CNC router to develop a combined printing and cutting system. This integration required modification to the overall system through mechanical, electrical, and software means to the existing 3-axis CNC milling system. A secondary z-axis was installed onto the router gantry for positioning of the printheads relative to the substrate, which required development of a separate homing routine to consistently position the printheads to a specified location. Based on the identified frequency response of the machine, a loop-shaping controller was designed for improved y-axis positioning, which is one of the main contributions to droplet placement accuracy. This resulted in a continuous motion tracking accuracy within ±20.2 µm at 250 mm/sec along a print pass (measured by 1.22 nm resolution linear encoder), which is significantly better than the industrial benchmark of ±100 µm. Extensive image processing and calibration methods were utilised on various substrate preparations of paper, wood, and coatings, to demonstrate the capability of the printing system and quantify the quality of print resolution. Calibration results tested on high-gloss Hewlett-Packard paper showed that the swath angle could be aligned within ±1°. Also, bidirectional printing could be used to reduce print time by at least 15% in multi-colour printing with comparable droplet placement accuracy to unidirectional printing. The inkjet system was successfully used to print custom designs on paper and, to a certain extent, on medium density fibreboard at a feed rate of 250 mm/sec. It was difficult to achieve satisfactory image results on wood, as the wood or paint grain was visible through the ink. Thus, without a white pre-coat, the printed image would appear significantly darker than the original image, even after adjusting the image in a graphics editor. For better quality results, it is recommended that greyscale printheads be implemented for greater resolution and a UV system should be investigated for more versatility in printing on different substrates such as glass, metals, plastics, and ceramics.

Manufactured products, such as furniture, laminate flooring, and large signs, are very labour intensive, time-consuming, and costly to produce as they require multiple coating and cutting operations on a series of independent machines, which can each introduce manufacturing errors between the tools and the work piece. By combining the processes of printing and milling, printing integrated manufacturing has the potential to eliminate some of these steps, significantly reduce errors, and preserve resources. Inkjet printing is an ideal method for both image transfer and coating operations due to its non-contact method of directly depositing various types of fluid onto a substrate. With improved positioning accuracy and droplet miniaturisation, inkjet printing could even be used for future applications like the mass-production of MEMS devices, which are traditionally fabricated with a highly complex process involving photolithography. This thesis presents the integration of a Xaar 126 inkjet printing system with an existing industrial flatbed CNC router to develop a combined printing and cutting system. This integration required modification to the overall system through mechanical, electrical, and software means to the existing 3-axis CNC milling system. A secondary z-axis was installed onto the router gantry for positioning of the printheads relative to the substrate, which required development of a separate homing routine to consistently position the printheads to a specified location. Based on the identified frequency response of the machine, a loop-shaping controller was designed for improved y-axis positioning, which is one of the main contributions to droplet placement accuracy. This resulted in a continuous motion tracking accuracy within ±20.2 µm at 250 mm/sec along a print pass (measured by 1.22 nm resolution linear encoder), which is significantly better than the industrial benchmark of ±100 µm. Extensive image processing and calibration methods were utilised on various substrate preparations of paper, wood, and coatings, to demonstrate the capability of the printing system and quantify the quality of print resolution. Calibration results tested on high-gloss Hewlett-Packard paper showed that the swath angle could be aligned within ±1°. Also, bidirectional printing could be used to reduce print time by at least 15% in multi-colour printing with comparable droplet placement accuracy to unidirectional printing. The inkjet system was successfully used to print custom designs on paper and, to a certain extent, on medium density fibreboard at a feed rate of 250 mm/sec. It was difficult to achieve satisfactory image results on wood, as the wood or paint grain was visible through the ink. Thus, without a white pre-coat, the printed image would appear significantly darker than the original image, even after adjusting the image in a graphics editor. For better quality results, it is recommended that greyscale printheads be implemented for greater resolution and a UV system should be investigated for more versatility in printing on different substrates such as glass, metals, plastics, and ceramics.