02: Molecular Level Understanding of Polymer Crystallization

This research is an NSF and DOE funded project where Akpalu is the principal investigator.

The formation of polymer crystals is a key step in the fabrication of polymeric fibers and films, as the morphology and properties of the final materials are strongly influenced by the processing conditions under which crystallization occurs. Because crystal formation depends on the molecular structure of polymer chains, there is a broad interest in correlating processing conditions with molecular structure of polymer chains. However, despite extensive investigation, the molecular mechanisms of polymer crystallization remain a subject of debate. This molecular level understanding can be achieved if clear structural information during early stage crystallization is available for distinguishing between proposed crystallization models, and for elucidating the influence of early stage crystallization on the final morphology of the polymer.

Recent results in our laboratory show that at the high temperatures required for resolving early stage polymer crystallization without the influence of lamellar crystal growth, clear structural information can be obtained by the combined use of polarized light and ultra-small angle X-ray scattering. Our results show that fractal objects with diffuse interfaces are formed initially, where the limiting slope of the scattering profiles increases from around 2 to 4 during early stage crystallization. This indicates that the interfaces of these domains sharpen with time. The interface sharpening process depends on crystallization temperature and the short chain branch length of the ethylene/olefin copolymers studied.

Our current efforts are to use our unique light and X-ray scattering capabilities to characterize the effect of nanoparticles on the crystallization of model synthetic and biopolymers.

Related Publications

• Zhicheng Xiao, Jan Ilavsky, Gabrielle G. Long and Yvonne A. Akpalu, “How do orientation fluctuations evolve to crystals?” in Lecture Notes in Physics: Progress in Understanding of Polymer Crystallization, Strobl (Eds.), Springer Press, 2007, Volume 714, Chapter 7.
• Z. Xiao, Y. A. Akpalu*, “New Insights into the characteristics of fluctuations during early stage crystallization of a polyethylene”, Polymer, accepted.