|Ph.D Thesis||Department of Chemistry|
|Supervisors:||Prof. Hoffman Alon|
|Dr. Eitan Grossman|
External surfaces of spacecrafts in low earth orbit (LEO) are exposed to the various constituents of the space environment, including atomic oxygen (AO) and solar UV radiation. The present work studies the interactions of various polyethylenes with different RF oxygen plasma components simulating the LEO environment. Polyethylene is considered as a model compound for investigating the effect of the structure on the morphology of eroded polymers. The polyethylenes were exposed in the afterglow region, beyond the RF reactor exit, to the different species emanating from the RF oxygen plasma. The exposed samples were characterized by various surface sensitive techniques, such as XPS, AFM, FTIR and more.
Erosion of the samples showed an etching rate that is dependent on the degree of crystallinity: the higher the crystallinity level the lower the erosion rate. The addition of VUV radiation to the AO flux resulted in a significant increase of the etching rate.
A process is reported whereby ordered nano domains are formed and a morphological reconstruction is generated into row-structure on the surface of Ultra-Strong, Ultra-High Molecular Weight Polyethylene (UHMWPE) fibers as a result of the simultaneous exposure to oxygen and UV radiation in the afterglow of RF oxygen plasma at ambient temperatures. The orientation of the rows is perpendicular to the fiber direction. A possible explanation for this phenomenon is that the combined irradiation resulted in selective etching of the amorphous phase and release of polyethylene nano-rods of which the fiber is composed. Subsequently these nano-rods self-assembled on the surface of the fiber into row-structures.