Mechanical properties and characterisation of substrates for flexible displays

This project is concerned with the electro-mechanical reliability and characterisation of ITO coated polyester substrates for use in touch screen and flexible display applications. Flexible display anode components such as ITO coated polyesters are common in almost all flexible display technologies. However, these hybrid thin systems are unusual in mechanical terms. There is a mismatch between the mechanical properties of the inorganic coating and the organic substrate. It is therefore important to investigate the electromechanical response of such flexible anodes under various stress states and deformation modes. It is also important to develop new mechanical testing techniques for flexible displays. Numerous experimental techniques were used in order to characterise and test the available ITO coated/uncoated PET and PEN substrates. Also, the development of new experimental mechanical testing methods, such as the biaxial 'bulge' apparatus, was undertaken. During this work, various ITO coated polyester substrates were mechanically tested under uniaxial tension, controlled buckling and biaxial tension. In-situ electrical resistance monitoring and ex-situ atomic force microscopy, were used in order to detect and characterise ITO failure mechanisms. Tribological investigation of bare polyester substrates was undertaken. Preliminary nanoscratch and nanoindentation studies were also conducted on coated and uncoated systems. Overall it was shown that ITO coated polyester flexible display electrodes can properly function up to relatively low strains. Electrical resistance generally does not recover during unloading in cyclic experiments. These factors currently limit the use of such components to slightly curbed displays. Various ITO failure modes were observed, depending on the applied deformation mode. It was also shown, that the ITO adhesive failure is as critical as cohesive failure

Non-Muscle Myosin II Isoforms Have Different Functions in Matrix Rearrangement by MDA-MB-231 Cells

The role of a stiffening extra-cellular matrix (ECM) in cancer progression is documented but poorly understood. Here we use a conditioning protocol to test the role of nonmuscle myosin II isoforms in cell mediated ECM arrangement using collagen constructs seeded with breast cancer cells expressing shRNA targeted to either the IIA or IIB heavy chain isoform. While there are several methods available to measure changes in the biophysical characteristics of the ECM, we wanted to use a method which allows for the measurement of global stiffness changes as well as a dynamic response from the sample over time. The conditioning protocol used allows the direct measurement of ECM stiffness. Using various treatments, it is possible to determine the contribution of various construct and cellular components to the overall construct stiffness. Using this assay, we show that both the IIA and IIB isoforms are necessary for efficient matrix remodeling by MDA-MB-231 breast cancer cells, as loss of either isoform changes the stiffness of the collagen constructs as measured using our conditioning protocol. Constructs containing only collagen had an elastic modulus of 0.40 Pascals (Pa), parental MDA-MB-231 constructs had an elastic modulus of 9.22 Pa, while IIA and IIB KD constructs had moduli of 3.42 and 7.20 Pa, respectively. We also calculated the cell and matrix contributions to the overall sample elastic modulus. Loss of either myosin isoform resulted in decreased cell stiffness, as well as a decrease in the stiffness of the cell-altered collagen matrices. While the total construct modulus for the IIB KD cells was lower than that of the parental cells, the IIB KD cell-altered matrices actually had a higher elastic modulus than the parental cell-altered matrices (4.73 versus 4.38 Pa). These results indicate that the IIA and IIB heavy chains play distinct and non-redundant roles in matrix remodeling

Graphene Flake Self-Assembly Enhancement via Stretchable Platforms and External Mechanical Stimuli

While the green production and application of 2D functional nanomaterials, such as graphene flakes, in films for stretchable and wearable technologies is a promising platform for advanced technologies, there are still challenges involved in the processing of the deposited material to improve properties such as electrical conductivity. In applications such as wearable biomedical and flexible energy devices, the widely used flexible and stretchable substrate materials are incompatible with high-temperature processing traditionally employed to improve the electrical properties, which necessitates alternative manufacturing approaches and new steps for enhancing the film functionality. We hypothesize that a mechanical stimulus, in the form of substrate straining, may provide such a low-energy approach for modifying deposited film properties through increased flake packing and reorientation. To this end, graphene flakes were exfoliated using an unexplored combination of ethanol and cellulose acetate butyrate for morphological and percolative electrical characterization prior to application on polydimethylsiloxane (PDMS) substrates as a flexible and stretchable electrically conductive platform. The deposited percolative free-standing films on PDMS were characterized via in situ resistance strain monitoring and surface morphology measurements over numerous strain cycles, with parameters extracted describing the dynamic modulation of the film’s electrical properties. A reduction in the film resistance and strain gauge factor was found to correlate with the surface roughness and densification of a sample’s (sub)surface and the applied strain. High surface roughness samples exhibited enhanced reduction in resistance as well as increased sensitivity to strain compared to samples with low surface roughness, corresponding to surface smoothing, which is related to the dynamic settling of graphene flakes on the substrate surface. This procedure of incorporating strain as a mechanical stimulus may find application as a manufacturing tool/step for the routine fabrication of stretchable and wearable devices, as a low energy and compatible approach, for enhancing the properties of such devices for either high sensitivity or low sensitivity of electrical resistance to substrate strain

Taking Professional Development From 2D to 3D: Design-Based Learning, 2D Modeling, and 3D Fabrication for Authentic Standards-Aligned Lesson Plans

There is currently significant interest in 3D fabrication in middle school classrooms. At its best 3D printing can be utilized in authentic design projects that integrate math, science, and technology, which facilitate deep learning by students. In essence, students are able to tinker in a virtual world using 3D design software and then tinker in the real world using printed parts. We describe a professional development activity we designed to enable middle school teachers who had taken part in a three-year Math Science Partnership program to authentically integrate 3D printing into design-based lessons. We include some examples of successful design-based lesson plans

Stimulus Responsive Nanoparticles

Disclosed are various embodiments of methods and systems related to stimulus responsive nanoparticles. In one embodiment includes a stimulus responsive nanoparticle system, the system includes a first electrode, a second electrode, and a plurality of elongated electro-responsive nanoparticles dispersed between the first and second electrodes, the plurality of electro-responsive nanorods configured to respond to an electric field established between the first and second electrodes

Biocompatible rapid few-layers-graphene synthesis in aqueous lignin solutions

Ultrasonic-Assisted Liquid Phase Exfoliation (UALPE) is considered one of the most promising approaches for the scale-up of graphene production. The process is based on the isolation and stabilization of layers of 2D materials, such as graphene: the selection of a proper stabilizing/exfoliating agent is crucial to achieve a stable Few-Layers-Graphene (FLG) dispersion. In the present work we propose the use of alkali lignin (AL) as a polymeric stabilizing agent for the rapid ( ≤3 hours) synthesis of FLG. Sonication time and graphite-to-lignin (Gr/AL) ratios were investigated as the primary operational parameters to identify the optimal working conditions. Spectroscopical characterization of the samples were employed to assess the quality of the synthesized material: the analysis of the Raman and XPS spectra provided insight on the number of layers and the nature of the limited defects introduced with the exfoliation procedure. Low-defectivity FLG was obtained at Gr/AL = 8 and a sonication time of 3 hours. Furthermore, Scan- ning Electron Microscopy and Dynamic Light Scattering were performed to investigate the size of the exfoliated flakes ( ∼400 nm). The procedure proposed represents a rapid route for the synthesis of FLG, which will be further explored for composites in chemiresistive devices

On the Unusual Amber Coloration of Nanoporous Sol-gel Processed Al-doped Silica Glass: An Experimental Study

Silica is the most abundant component on the earth’s surface. It plays an important role in many natural processes. Silica is also a critical material for a wide range of technical applications such as in optics and electronics. In this work, we discuss our recent experimental observation of the unusual amber coloration of aluminum doped sol-gel glass that has not been reported in the past. We characterized Al-doped sol-gel glasses, prepared at different sintering temperature, using a plethora of techniques to investigate the origin of this unusual coloration and to understand their structural and chemical properties. We used these experimental results to test a number of possible coloring mechanisms. The results suggested this coloring is likely caused by temperature-dependent aluminum-associated defect centers associated with different amorphous-to-crystalline ratios of the annealed sol-gel silica glass structures

The Effects of Corrosion, Fatigue, and Corrosion-fatigue of Multilayer Coated Polyesters for Flexible Electronics Applications

We investigated the electrical and optical properties of ITO/Ag-alloy/ITO films in a corrosive NaCl solution. The effects of bending fatigue combined with aggressive environments pro-vided by the salt solution were also studied. It is shown that exposure to the salt solution can cause the ITO/Ag-alloy/ITO performance to degrade over time. In addition, greater changes in electrical resistance and lower values of optical transmittance were observed at higher concentrations of the salt solution. The combination of stress and corrosion by the aqueous NaCl solution was found to significantly reduce the conductivity of the ITO/Ag-alloy/ITO film. Furthermore, it is shown that the presence of structural defects in the deposited films can provide a driving force to form Ag agglomerations that, in turn, degrade the conductivity of the ITO/Ag-alloy/ITO film. This suggests that defects in the film should be minimized to avoid excessive corrosion

Mechanical properties of amorphous indium-gallium-zinc oxide thin films on compliant substrates for flexible optoelectronic devices

Amorphous indium–gallium–zinc-oxide (a-IGZO) thin films were deposited using RF magnetron sputtering on polyethylene naphthalate (PEN) and polyethylene terephthalate (PET) flexible substrates and their mechanical flexibility investigated using uniaxial tensile and buckling tests coupled with in situ optical microscopy. The uniaxial fragmentation test demonstrated that the crack onset strain of the IGZO/PEN was ~ 2.9%, which is slightly higher than that of IGZO/PET. Also, uniaxial tensile crack density analysis suggests that the saturated crack spacing of the film is strongly dependent on the mechanical properties of the underlying polymer substrate. Buckling test results suggest that the crack onset strain (equal to ~ 1.2%, of the IGZO/polymer samples flexed in compression to ~ 5.7 mm concave radius of curvature) is higher than that of the samples flexed with the film being in tension (convex bending) regardless whether the substrate is PEN or PET. The saturated crack density of a-IGZO film under the compression buckling mode is smaller than that of the film under the tensile buckling mode. This could be attributed to the fact that the tensile stress encouraged this crack formation originating from surface defects in the coating. It could also be due to the buckling delamination of the thin coating from the substrate at a lower strain than that at which a crack initiates during flexing in compression. These results provide useful information on the mechanical reliability of a-IGZO films for the development of flexible electronics.The authors would like to thank DuPont-Teijin for donating polymer samples. We would also like to thank Mr. Frank Biddlestone for his technical support and Mr. Warren Hay for his help in the workshop. Financial support from the Kurdistan Regional Government HCDP programme is gratefully acknowledged. The atomic force microscope used in this research was obtained, through Birmingham Science City: Innovative Uses for Advanced Materials in the Modern World (West Midlands Centre for Advanced Materials Project 2), with support from Advantage West Midlands (AWM) (DD-07) and partly funded by the European Regional Development Fund (ERDF) (SY/SP80). R.W. gratefully acknowledges funding from the EPSRC Centre for Doctoral Training in Photonic Systems Development.This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.tsf.2015.09.05

Direct foam writing in microgravity

Herein we report 2D printing in microgravity of aqueous-based foams containing metal oxide nanoparticles. Such hierarchical foams have potential space applications, for example for in situ habitat repair work, or for UV shielding. Foam line patterns of a TiO2-containing foam have been printed onto glass substrates via Direct Foam Writing (DFW) under microgravity conditions through a parabolic aircraft flight. Initial characterization of the foam properties (printed foam line width, bubble size, etc.) are presented. It has been found that gravity plays a significant role in the process of direct foam writing. The foam spread less over the substrate when deposited in microgravity as compared to Earth gravity. This had a direct impact on the cross-sectional area and surface roughness of the printed lines. Additionally, the contact angle of deionized water on a film exposed to microgravity was higher than that of a film not exposed to microgravity, due to the increased surface roughness of films exposed to microgravity