ABSTRACT
Thermo-analytical studies of thermoset adhesives, either during research and development or in quality assurance activities, involve the application of various analytical equipment for adhesive characterization, from initial mixing to final product decomposition. Gelation is usually measured with rheometers or dynamic mechanical analyzers (DMAs); curing, post-curing, and curing kinetics are often studied using differential scanning calorimetry (DSC). Glass transition temperature (Tg) is measured via DSC or DMA, and finally, thermal decomposition measurements are done using thermal gravimetric analysis. Here, we present a new curing kinetics optimization module (C-KOM), an extension to an axial DMA, and a protocol for its usage, which combines elements from all of the above thermo-analytical techniques into one tool. As a case study, we apply C-KOM to investigate the effect of the curing temperature on the physical properties of an epoxy adhesive including gelation and end of cure points as well as its Tg. The data collected via C-KOM were used to extract the adhesive's curing reaction rates and its activation energy. Our research allowed us to compare and evaluate previously suggested curing procedures and assess their validity. As a final step, the thermal decomposition temperature of the epoxy adhesive was also identified via C-KOM. The newly suggested C-KOM setup provides a fast path toward characterization and optimization of the curing processes of thermoset materials in a way that was not available before.
ABSTRACT
The materials of spacecraft external surfaces in low Earth orbit (LEO) are exposed to the various constituents of the space environment, including atomic oxygen (AO) and solar ultra violet (UV) radiation. Material degradation and erosion by LEO are simulated in ground laboratories using a variety of experimental facilities, each with their respective limitations. rf oxygen plasma is a simulation facility widely used for materials screening for LEO application. However, the complex plasma environment, which contains, in addition to the neutral oxygen atoms, excited species, electrons, and ions as well as vacuum ultraviolet (VUV) radiation, might lead to erroneous determination of materials reactivity with respect to LEO. This paper describes the development of a simple, low cost rf plasma system to produce a well-defined AO and VUV environment. The new system constrained the afterglow flow through two right-angle turns. The afterglow was characterized at three specific locations by (i) optical emission spectroscopy for assessment of electronically excited states, (ii) current measurements, and (iii) UV radiation measurements. KaptonR samples were exposed at the three specific locations in the system and characterized by mass loss for etch rate evaluation, and atomic force microscopy for surface modification. It was found that there is a significant reduction in ionic species, excited species, and UV radiation as the afterglow advances through the right-angle turns. The reduction in charged particle flux is due to recombination within the afterglow as well as neutralization by colliding with the grounded metal chamber walls; similar decrease in UV radiation flux occurs through radiation absorption by the chamber walls. Finally, it is shown that the ground state AO is the dominant reactive specie of the plasma afterglow after passing through the two right-angle turns.
ABSTRACT
This paper describes computational and experimental work on pattern formation in Drosophila egg development (oogenesis), an established experimental model for studying cell fate diversification in developing tissues. Epidermal growth factor receptor (EGFR) is a key regulator of pattern formation and morphogenesis in Drosophila oogenesis. EGFR signalling in oogenesis can be genetically manipulated and monitored at many levels, leading to large sets of heterogeneous data that enable the formulation of increasingly quantitative models of pattern formation in these systems.
