Influence of POSS Type on the Space Environment Durability of Epoxy-POSS Nanocomposites

In order to use polymers at low Earth orbit (LEO) environment, they must be protected against atomic oxygen (AO) erosion. A promising protection strategy is to incorporate polyhedral oligomeric silsesquioxane (POSS) molecules into the polymer backbone. In this study, the space durability of epoxy-POSS (EPOSS) nanocomposites was investigated. Two types of POSS molecules were incorporated separately—amine-based and epoxy-based. The outgassing properties of the EPOSS, in terms of total mass loss, collected volatile condensable material, and water vapor regain were measured as a function of POSS type and content. The AO durability was studied using a ground-based AO simulation system. Surface compositions of EPOSS were studied using high-resolution scanning electron microscopy and X-ray photoelectron spectroscopy. It was found that with respect to the outgassing properties, only some of the EPOSS compositions were suitable for the ultrahigh vacuum space environment, and that the POSS type and content had a strong effect on their outgassing properties. Regardless of the POSS type being used, the AO durability improved significantly. This improvement is attributed to the formation of a self-passivated AO durable SiO2 layer, and demonstrates the potential use of EPOSS as a qualified nanocomposite for space applications

Cure kinetics of bismaleimides as basis for polyimidelike inks for PolyJet3Dprinting

Since polyimides are well known for their excellent chemical and thermal stability and outstanding mechanical properties there is increasing interest in developing polyimidebased inks to produce additively manufactured parts with properties superior to those of currently available materials. Usage of bismaleimides (BMI) as precursors allows polyimides to be fabricated via PolyJet printing (Stratasys Ltd., Rehovot, Israel). Characterization of the curing kinetics is a central part of process development, as fast curing initiated by UV light is desired. Here, a comprehensive study of thermal and UV curing of BMI oligomers with various molecular weights and chemical structures is presented. Fourier transform infrared spectroscopy serves as a tool for determining the curing degree. Furthermore, an estimation of the activation energy for thermal curing is performed. UV curing of the selected BMIs leads to highly crosslinked, thermoset polymers with excellent chemical resistance and thermal stability which are of great interest for PolyJet 3D printing.685937(VLID)356919

High Rate of Hydrogen Incorporation in Vertically Aligned Carbon Nanotubes during Initial Stages of Growth Quantified by Elastic Recoil Detection

We quantified the amount of hydrogen in as-grown vertically aligned multiwall CNTs at different stages of growth using elastic recoil detection analysis (ERDA). We suggest that hydrogen is associated with atomic defects and/or amorphous carbon impurities formed at earlier deposition stages. We found that the highest amount of hydrogen (2.3 wt %) was incorporated during the initial growth stage (15–20 s). Our results show a decrease of hydrogen content with increasing deposition time and/or with decreasing growth rate, which points to dynamical self-annealing of hydrogen-saturated defects. Consequently, the decrease of hydrogen-related defects leads to a higher quality of MWCNTs, which can be easily detected by ERDA. This research provides new insight into the nanotube growth mechanism and provides a new characterization approach for quantifying hydrogen-saturated atomic defects in MWCNTs

Novel timed and self-resistive heating shape memory polymer hybrid for large area and energy efficient application

Shape memory polymers (SMPs) are a polymeric smart material that can register two or more temporary shapes and transform to one another through an external stimulus. Despite their compactness and customizability, SMPs haven't been able to be adopted for mainstream applications. Since the majority of SMPs are triggered by heat, and SMPs have a very poor thermal conductivity, large thermal gradients within the polymer appear which cause slow response, inhomogeneous heat distribution and thus non-uniform transformation of shapes and cracks. Many have attempted to improve their thermal performance through the incorporation of filler-based nanomaterials. However, the outcome is ineffective as the spatial dispersion of fillers within the SMP is inhomogeneous and leads to performance loss. Contrastingly, the herein presented new class of nanocomposite-SMP, composed by 3D-foam fillers, showcase a much more efficient SMP adaptable to larger area with faster transformation speed and without any performance loss. Furthermore, the improved thermal properties lead to a decrease in required input energy, as well as render the SMP a self-heating capability which can be further designed into timed multi-step SMP behavior

POSS enhanced 3D graphene - polyimide film for atomic oxygen endurance in low earth orbit space environment

Recently, 3D-graphene infused polyimide (3DC/PI) films have shown to be an effective protection coating for electrostatic discharge in spacecraft. However, these films are not suitable for Low Earth Orbit (LEO) due to atomic oxygen (AO) erosion. Here, we used Polyhedral Oligomeric Silsesquioxane (POSS) to enhance the AO durability of 3D-C/PI films. Three different ways of adding POSS to the composite films were studied with ground-based AO exposure. For all infusion approaches, their electrical conductivity behaviour is well preserved and the presence of POSS results in reduced AO erosion yield. Of all the methods studied here, incorporating POSS directly into PI results in the lowest erosion yield of 4.67 × 10−25 cm3/O-atom (one order of magnitude lower than that of Kapton). Adding POSS to PI, extends the durability of the composite film beyond 10 years, making it an ideal protective material for long term mission in LEO.Accepted versio