Abstract by Shawn Averett
Chemistry and Biochemistry
Surface Response of High Density Polyethylene to Mechanical Deformation
It is projected that the global demand for polyethylene will reach 99.6 million tons, enough to fill nearly thirty four thousand NFL stadiums, by 2018. This huge amount of polymer will be used to make a wide range of products including plastic bags, pipes, cosmetics, and artificial joints. In addition to being an important material in its own right, polyethylene is also used as a model for understanding the behavior of other semicrystalline polymers like nylon and polypropylene. Because of its important role, polyethylene has been extensively studied for decades, however a molecular level understanding of how polyethylene surfaces respond to mechanical stress has not been developed. Because chemical interactions and failure processes both start at the material surface, an in depth understanding of this region is critical. We used vibrational sum frequency generation spectroscopy (VSFG) to probe structural changes due to mechanical deformation. When samples were pulled to the point that a neck formed, polymer chains were consistently found to be aligned with the direction of pull with the methylene groups oriented roughly normal to the surface.