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

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

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