Layer-by-Layer Assembled Nanowire Networks Enable Graph Theoretical Design of Multifunctional Coatings

Multifunctional coatings are central for information, biomedical, transportation and energy technologies. These coatings must possess hard-to-attain properties and be scalable, adaptable, and sustainable, which makes layer-by-layer assembly (LBL) of nanomaterials uniquely suitable for these technologies. What remains largely unexplored is that LBL enables computational methodologies for structural design of these composites. Utilizing silver nanowires (NWs), we develop and validate a graph theoretical (GT) description of their LBL composites. GT successfully describes the multilayer structure with nonrandom disorder and enables simultaneous rapid assessment of several properties of electrical conductivity, electromagnetic transparency, and anisotropy. GT models for property assessment can be rapidly validated due to (1) quasi-2D confinement of NWs and (2) accurate microscopy data for stochastic organization of the NW networks. We finally show that spray-assisted LBL offers direct translation of the GT-based design of composite coatings to additive, scalable manufacturing of drone wings with straightforward extensions to other technologies

Aging of polymeric composite specimens for 5000 hours at elevated pressure and temperature, Composite Science and Technology 61

] 2s open-hole compression. The materials used were selected to evaluate the test method and not as candidate materials for use at higher temperatures. The test results show a distinct accelerating eect with the use of elevated pressures especially for the tensile shear coupons. The results also suggest that elevated pressure may be a good tool for signi®cantly reducing screening times for material that will be subjected to long exposures in oxygen-containing environments at elevated temperatures.

Controlling the sub-molecular motions to increase the glass transition temperature of polymers

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Insights into the Mechanism and Kinetics of Thermo-Oxidative Degradation of HFPE High Performance Polymer

The growing requisite for materials having high thermo-oxidative stability makes the design and development of high performance materials an active area of research. Fluorination of the polymer backbone is a widely applied strategy to improve various properties of the polymer, most importantly the thermo-oxidative stability. Many of these fluorinated polymers are known to have thermo-oxidative stability up to 700 K. However, for space and aerospace applications, it is important to improve its thermo-oxidative stability beyond 700 K. Molecular-level details of the thermo-oxidative degradation of such polymers can provide vital information to improve the polymer. In this spirit, we have applied quantum mechanical and microkinetic analysis to scrutinize the mechanism and kinetics of the thermo-oxidative degradation of a fluorinated polymer with phenylethenyl end-cap, HFPE. This study gives an insight into the thermo-oxidative degradation of HFPE and explains most of the experimental observations on the thermo-oxidative degradation of this polymer. Thermolysis of C–CF₃ bond in the dianhydride component (6FDA) of HFPE is found to be the rate-determining step of the degradation. Reaction pathways that are responsible for the experimentally observed weight loss of the polymer is also scrutinized. On the basis of these results, we propose a modification of HFPE polymer to improve its thermo-oxidative stability

Low-density and high-modulus carbon fibers from polyacrylonitrile with honeycomb structure

The density of commercially available polyacrylonitrile-based carbon fibers is in the range of 1.75-1.93 g/cm(3). It will be of great benefit to reduce the density of carbon fiber without compromising mechanical properties, so that high-performance structures made from such fibers can be lighter than those made from the solid carbon fibers. With the goal to produce high-strength and high-modulus carbon fibers with densities in the range of 0.9-1.3 g/cm(3), polyacrylonitrile (PAN) based precursor fibers were produced with a honeycomb structure. Using dry-jet wet spinning and an islands-in-a-sea geometry bicomponent spinning method, honeycomb precursor fibers were manufactured that consisted of PAN as the sea component and poly(methyl methacrylate) (PMMA) as the islands component. Subsequently, the precursor fibers were stabilized and carbonized to produce hollow carbon fibers. Resulting carbon fibers have an estimated density of around 1.2 g/cm(3) with high tensile modulus of up to 209 N/tex. Raman spectroscopy mapping of the carbonized honeycomb fiber cross-section exhibited a strong Raman G-band intensity not only at the outer surface of the carbon fiber but also at the surface of inner walls of the honeycomb structure, suggesting that highly ordered graphitic structure was developed at these regions.close