Recent research has begun to evaluate the role that the distribution of nanoscale fractional free volume (FFV) plays in the service life of high performance materials such as aramid or ultrahigh molar mass polyethylene fibers and composites. Such materials are formulated to maximize mechanical properties such as strain to failure and ultimate tensile strength, often at the expense of properties such as compressive modulus. The low compressive modulus of many such materials renders them susceptible to kink banding and void formation, which alters the free volume of the material. Recent research has also shown that kink banded regions of high performance fibers are more susceptible to mechanisms of degradation such as thermo-oxidation, which have been shown to reduce the ultimate tensile strength of the material. Positron annihilation lifetime spectroscopy (PALS) is a novel technique used to investigate voids or pores in many different materials that has been previously shown promise for the evaluation of FFV in high strength fibers and composites. The goal of this research is to correlate changes in FFV with changes in physical and chemical properties due to artificial ageing. Candidates should have experience with characterization of high strength fibers through techniques such as mechanical testing, positron annihilation lifetime spectroscopy, molecular spectroscopy, and atomic force microscopy

 

References

Forster AL, et al: “Long Term Stability of UHMWPE Fibers.” Mechanics of Composites and Multifunctional Materials 7: 369, 2016

Forster AL, et al: “Long Term Stability of UHMWPE Fibers.” Polymer Degradation and Stability 114: 45, 2015

Forster AL, et al: "Hydrolytic stability of polybenzobisoxazole and polyterephthalamide body armor.” Polymer Degradation and Stability 96: 247, 2011

 

key words

Positron annihilation lifetime spectroscopy; Polymers; High strength fibers; Composites; Body armor; Ballistic resistant; Long term stability; Artificial ageing;

Citizenship:  Open to U.S. citizens

Level:  Open to Postdoctoral applicants