Application of Two-Dimensional Correlation Analysis to Explosives Detection and Polymer Crystallization

Citation

Smirnova, Diana Sergeievna (2010) Application of Two-Dimensional Correlation Analysis to Explosives Detection and Polymer Crystallization. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/7PAR-VK52. https://resolver.caltech.edu/CaltechETD:etd-09112009-132932

Abstract

This thesis presents two novel applications of two-dimensional (2D) correlation analysis: (1) long standoff detection of explosives and (2) morphology development in semicrystalline materials.

Due to the dangers of improvised explosive devices (IEDs), effective detection of explosives at standoff distances can save lives. A scheme based on 2D correlation analysis in conjunction with thermal modulation is proposed to overcome weak signals that plague long standoff detection. Implementation of 2D correlation analysis results in significant enhancement of explosive signals relative to background. Effective separation of explosive features resulting from their unstable nature compared to common contaminants is demonstrated for two biogenic compounds. Several aspects of 2D correlation analysis are examined to optimize effectiveness of detection.

Ultimate physical properties of semicrystalline materials are directly related to their morphology through molecular characteristics and processing conditions. The effects of different molecular characteristics on morphology of model hydrogenated polybutadienes are examined by 2D correlation analysis of x-ray scattering data.

Model short-chain branched (SCB) polyethylenes are found to crystallize in three regimes during quiescent temperature ramps. "Primary-irreversible" crystallization occurs at the highest temperatures as primary lamellae propagate through unconstrained melt. During "secondary-irreversible" crystallization at intermediate temperatures, secondary lamellae grow in the largest non-crystalline regions between primary lamellae. “Reversible” crystallization at low temperatures is marked by the formation of fringed micelles. This is the first time that a physical justification is presented for the separation of the irreversible crystallization into primary- and secondary-irreversible regimes.

Each regime is identified by unique features in 2D correlation plots. Two-dimensional correlation analysis provides unique insight into subtle changes in morphology, such as the development of density heterogeneities in non-crystalline regions.

The presence of short-chain branches is found to have a profound, diminishing effect on the formation of oriented structures in response to flow-induced crystallization, which is further examined through blends containing linear and SCB polyethylene. Evidence presented suggests that a buildup of chain defects at the growth front results in a transition from oriented to isotropic crystallization. It is proposed that size of crystal structures can be controlled by dictating the amount of copolymer incorporated during crystallization.

Thesis Files