Coated polymers, mass loss

The erosion yield of a polymer is typically measured by two methods (1) recession and (2) mass loss. Recession measurements are made by masking an area of a sample surface from attack and measuring the step height difference between exposed and unexposed areas. The thickness loss divided by the exposure fluence is the erosion yield. Mass loss measurements are made either by weighing a sample before and after exposure or by monitoring the mass loss in situ of a material that was coated onto a quartz crystal microbalance. Care must be taken in mass loss measurements to ensure that outgassing from the material in the vacuum of the exposure environment does not affect the results. The calculation of the erosion yield from a mass loss measurement requires knowledge of the density of the material and the surface area exposed, as well as the exposure fluence. 

Reimer [1121 found a moderate reduction in mass loss rate for coated PMMA. Salih and Cosslett [113] coated an aromatic organic crystal and found that the dose needed to destroy the diffraction pattern increased by five times. Fryer and Holland [114] found factors of three to ten times improvement for a wide range of organic crystals. No reports have been published for diffraction lifetimes from coated polymer films, but with a very simple technique promising significant gains, it is worth a try. 

One approach to compensate for buoyancy and general baseline issues encountered with very small mass loss is to perform a second experiment with a closely matching inert sample and subsequently subtracting this blank experiment. A series of such experiments can be stored for future use. An excellent example of this technique was the determination of the coating thickness on fused-silica fibers (Gallagher 1992). Fibers were initially heated in an oxidizing atmosphere to burn off the very thin polymer coating. They were... 

Polymers, their blends and composites may be exposed to radiation during radiation processing, or when exposed to irradiation (e.g., irradiative sterilization, exposure to radiation in space, exposure to radiation during wire coating) In space (hard vacuum and cold) the radiation may lead to mass loss (progressive surface erosion). However, in inert atmosphere, irradiation may cause crossUnking, degradation or both. 

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