Date of Award

Fall 2019

Document Type

Open Access Dissertation

Department

Chemistry and Biochemistry

First Advisor

Michael L. Myrick

Abstract

The detection of blood on fabrics for forensic purposes is a widely studied topic in forensic science, and to that end, effort in this laboratory has been devoted to developing a thermal imaging method called steam thermography. Steam thermography is a method used to enhance chemical contrast in thermographic images by exposing a surface to water vapor during imaging. The exposure of water vapor to the surface generates heat, and can differentially increase the thermographically measured apparent temperature of imaged surfaces. This can result in thermographic contrast between surfaces with different chemical properties. Previously reported proposed mechanisms to describe the chemical contrast enhancement of dried blood stains on fabric during a steam thermography measurement include a radiant heat transfer which warms the blood and fabric differentially, a convective transfer of heat from the water vapor to the blood stains and fabric which result in a differential heating, the deposition of condensed airborne water droplets which results in a differential change in apparent temperature, a differential condensation of liquid water on the sample surface, a change in thermal emissivities of the bloodstain and fabric such that the difference in the emissive power of the surfaces increases, and lastly, a differential adsorption of the water vapor. The studies reported in this manuscript address the potential mechanisms of the enhanced chemical contrast observed during a steam thermography measurement, and in doing so provide evidence that the adsorption of water vapor is the primary (and in specifically designed experiments, the only) mechanism of the enhancement. Thermographic contrast enhancement for dried blood on acrylic, nylon, cotton, and polyester fabrics is demonstrated, along with measurements describing the change in emissivity as each of the fabrics and dried blood on acrylic fabric are exposed to varying amounts of humidity. The degree of contrast enhancement between dried blood stains on the above mentioned fabric substrates and the blank fabrics is also reported for the exposure of the samples to eight other solvent vapors during thermal imaging. Additionally, the effect to a steam thermography measurement of the silanization of a bloodstained cotton fabric using trimethylmethoxysilane is described.

Available for download on Wednesday, December 16, 2020

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