Processing and characterization of silver-filled conductive polysulfide sealants for aerospace applications.

Polysulfide (PS) rubbers have been widely used as high performance sealants to line or seal aircraft fuel tanks. However, safety concerns arise when electrostatic charges are built up due to the motion of flammable fuels. In this report, electrically conductive sealants were designed in order to dissipate these hazardous charges. Silver fillers with various sizes and surface coatings were incorporated into a polysulfide matrix to make conductive sealants. The low electrical conductivity of the sealants led to the assumption that unique filler-resin interactions occurred at their interfaces. To verify this assumption, various characterization methods were employed to investigate the chemical, thermal, morphological, electrical, and mechanical properties of the sealants. In addition, carbon fillers and other room temperature-cured polymer resins were used for comparative study. The systematic analysis revealed that the formation of coordination compounds at silver/PS interfaces could block electron conduction pathways between fillers. Based on the chemical understanding, post cure thermal annealing was utilized to break the coordinated bonds and restore high conductivity (>106 S m-1) of the sealants. Conductivity change as a function of annealing temperature and time was also explored to optimize processing conditions.

Trade-off between Gradual Set and On/Off Ratio in HfOx-Based Analog Memory with a Thin SiOx Barrier Layer.

HfOx-based synapses are widely accepted as a viable candidate for both in-memory and neuromorphic computing. Resistance change in oxide-based synapses is caused by the motion of oxygen vacancies. HfOx-based synapses typically demonstrate an abrupt nonlinear resistance change under positive bias application (set), limiting their viability as analog memory. In this work, a thin barrier layer of AlOx or SiOx is added to the bottom electrode/oxide interface to slow the migration of oxygen vacancies. Electrical results show that the resistance change in HfOx/SiOx devices is more controlled than the HfOx devices during the set. While the on/off ratio for the HfOx/SiOx devices is still large (∼10), it is shown to be smaller than that of HfOx/AlOx and HfOx devices. Finite element modeling suggests that the slower oxygen vacancy migration in HfOx/SiOx devices during reset results in a narrower rupture region in the conductive filament. The narrower rupture region causes a lower high resistance state and, thus, a smaller on/off ratio for the HfOx/SiOx devices. Overall, the results show that slowing the motion of oxygen vacancies in the barrier layer devices improves the resistance change during the set but lowers the on/off ratio.

Surface Modification of Backsheets Using Coupling Agents for Roll-To-Roll Processed Thin-Film Solar Photovoltaic (PV) Module Packaging Application.

For many flexible electronic and photonic devices, moisture stability is one of the most important factors that affects its short- and long-term performance. To maintain the performance, the device should be packaged in such a way that it hermetically blocks moisture from the device; however, in practice, it is rather difficult to achieve. The more practical solution is to impede the moisture ingress to the device. In optoelectronic devices that will be outdoors like solar cells, the interfacial adhesion strength between the encapsulant layer (adhesive) and a moisture barrier layer is also a critical parameter. This paper presents surface modifications of poly(ethylene terephthalate) (PET) carrier films, one of the layers in the trilayer barrier film that directly adheres to an encapsulant, using chemical, UV/ozone, and both treatments to improve adhesion with the thermoset encapsulant polymer material. Whereas previous studies also utilized treatment methods to increase the wettability characteristics, in this paper, we not only present the results of the adhesion strength upon various techniques to achieve good adhesion but also screen their behavior upon exposure to a damp-heat (60 °C, 90% RH) environment. We found that the combined treatment method increases the adhesion by up to 12.1-fold and demonstrates up to a 200% increase in adhesion strength even upon our severe damp-heat environmental condition.

Atomic Modulation of 3D Conductive Frameworks Boost Performance of MnO2 for Coaxial Fiber-Shaped Supercapacitors.

Coaxial fiber-shaped supercapacitors are a promising class of energy storage devices requiring high performance for flexible and miniature electronic devices. Yet, they are still struggling from inferior energy density, which comes from the limited choices in materials and structure used. Here, Zn-doped CuO nanowires were designed as 3D framework for aligned distributing high mass loading of MnO2 nanosheets. Zn could be introduced into the CuO crystal lattice to tune the covalency character and thus improve charge transport. The Zn-CuO@MnO2 as positive electrode obtained superior performance without sacrificing its areal and gravimetric capacitances with the increasing of mass loading of MnO2 due to 3D Zn-CuO framework enabling efficient electron transport. A novel category of free-standing asymmetric coaxial fiber-shaped supercapacitor based on Zn0.11CuO@MnO2 core electrode possesses superior specific capacitance and enhanced cell potential window. This asymmetric coaxial structure provides superior performance including higher capacity and better stability under deformation because of sufficient contact between the electrodes and electrolyte. Based on these advantages, the as-prepared asymmetric coaxial fiber-shaped supercapacitor exhibits a high specific capacitance of 296.6 mF cm-2 and energy density of 133.47 µWh cm-2. In addition, its capacitance retention reaches 76.57% after bending 10,000 times, which demonstrates as-prepared device's excellent flexibility and long-term cycling stability.