We are developing photopolymer resins with a toughness exceeding 25 MJ/m3, with a strain capacity of >200%, which are low odor, and which can be additively manufactured into a mesh of effective density <50 kg/m3 with individual strut thickness of <250 µm. We are optimizing placement of individual Digital Micromirror Device (DMD) chips (visual field overlap, optics train, staggering, rotation) in LightBars™, which consist of arrays of up to 64 DMDs with sufficient overlap to cure part layers at an anticipated 10 mm/sec to cover 500 mm wide at a voxel resolution of <200 µm such that each voxel is “patterned” by >1,000 different mirrors. Different resins have been tailored with different additive cocktails for rapid manufacturing at different wavelengths ranging from 355 nm to 385 nm to 405 nm.
We made low-resistance electrodes for a dielectric elastomer system (DES) without the use of thin film deposition or wet lab processes by utilizing a stretchable conductive fabric, Less EMF Stretch Conductive Fabric (SCF), for electrode material. Carbon-based DES electrodes are easy to make, but they have high resistances (kilo ohms) that hamper dynamic operation and reduce energy efficiency. Metal and hydrogel DES electrodes have much lower resistances (tens to hundreds of ohms), but they require complex manufacturing processes, such as thin film deposition or wet lab synthesis. Conductive fabrics can have low resistance and they can be made into DES electrodes with merely a laser cutter and a dry lab environment, but their stiffness may hinder DES performance. This work reports electrical and mechanical properties of SCF and a more compliant, though less conductive fabric, MedTex P70+B, and describes the assembly and performance of DES variable stiffness modules using them.
SCF had low sheet resistance, less than 3.0 ohm/square even during 125% biaxial stretch, and both fabrics stretched beyond 200 % uniaxial elongation before mechanical failure. The assembly of modules with conductive fabric electrodes was comparable in terms of difficulty to that with carbon powder electrodes, and produced functional modules. However, the stiffness of the fabrics diminished DES stiffness-reduction performance to merely 12.8 % and 13.4 % compared to the 24.5 % stiffness reduction a DES module with carbon powder electrodes achieved. Future work should investigate or develop more compliant conductive fabrics that would yield greater DES performance.
Solution deposition has potential for highly cost-effective fabrication of thin film transistors (TFTs) on flexible substrates. Shape memory polymer (SMP), with improved thermal mechanical response, may enable large-area flexible devices, as well as add control to the product shape and modulus. Until date, TFTs made on SMP substrates have been limited to vacuum-deposition methods. While TFTs processed through more economical solution-based techniques achieve device performance close to their vacuum-processed counterparts, they have not yet been demonstrated on SMP substrates due to the required high calcination temperatures (> 500 °C). To take full advantages of SMP, low temperature (< 200 °C) solution-based processing is highly desirable. Compatibility of the deposition process with the substrate and previously deposited films is essential. Here, we develop a process that incorporates direct UV patterning that would allow for fabrication of oxide TFTs on SMP using a reduced number of processing steps. Rigid In2O3 TFTs, deposited from solution-combustion synthesis, are fabricated on Si substrates with different solution-deposited dielectrics to evaluate their potential for transferring to SMP.
In this talk, we will discuss recent advances in the science and engineering of organic light-emitting diodes (OLEDs). First, we will focus on materials in which light emission involves the process of thermally activated delayed fluorescence (TADF). In these materials, triplet excited states can convert into optically emissive singlet excited states by reverse intersystem crossing, allowing for nearly 100% internal quantum efficiency. This process can be used to design a new class of materials that are all organic, offering a lower cost alternative to conventional electrophosphorescent materials that contain heavy and expensive elements such as Pt and Ir. We will discuss molecular design strategies and present examples of materials that can be used as emitters or hosts in the emissive layer.
In a second part of this talk, we will review recent progress in fabricating OLEDs on shape memory polymer substrates (SMPs). SMPs are mechanically active, smart materials that can exhibit a significant drop in modulus once an external stimulus such as temperature is applied. In their rubbery state upon heating, the SMP can be easily deformed by external stresses into a temporary geometric configuration that can be retained even after the stress is removed by cooling the SMP to below the glass transition temperature. Reheating the SMP causes strain relaxation within the polymer network and induces recovery of its original shape. We will discuss how these unique mechanical properties can also be extended to a new class of OLEDs.
We demonstrate top-gate organic field-effect transistors (OFETs) with a bilayer gate dielectric and doped contacts fabricated on shape-memory polymer (SMP) substrates. SMPs exhibit large variations in Young’s modulus dependent on temperature and have the ability to fix two or more geometric configurations when a proper stimulus is applied. These unique properties make SMPs desirable for three-dimensional shape applications of OFETs. The electrical properties of OFETs on SMP substrates are presented and compared to those of OFETs on traditional glass substrates.
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