Wednesday  |  Carnegie III  |  10:50 AM–11:10 AM

#13332, Elucidation of the Creep Response of Polymers using Light-matter Interactions

Polymers are notorious for their rate and time-dependent properties such that they exhibit high sensitivity to loading rate and duration. Therefore, polymers creep poses several technological challenges when this class of materials is integrated into load-bearing applications. Polyurea is used as a model material, where samples are loaded for an extended duration while nondestructively observing the molecular evolution using electromagnetic waves. Polyurea is a thermoset elastomer with superior mechanical properties such as high extensibility, water and chemical resistance, and excellent impact mitigation. These attributes exemplify the suitability of polyurea for many industrial applications. This research aims to elucidate the molecular mechanisms responsible for the creep response of elastomeric polymers. Specifically, the loaded polyurea samples are interrogated using a developed in-house terahertz wave spectrometer, operating in the transmission mode. Terahertz time-domain spectroscopy (THz-TDS) is conducive for the investigation of polymers during loading due to the penetrative, nondestructive, and nonionizing nature of terahertz waves. Polyurea samples are extracted from films, with a thickness of 100 um, fabricated using spin coating technique. This thickness was selected based on the available bandwidth of the THz-TDS spectrometer. The samples are loaded for three decades of time using newly developed magnetic clamps to ensure uniform loading throughout the measurement duration. The spectroscopic data is analyzed in the time and frequency domains to extract evolution in the refractive index, related to entropic changes in the material. Concurrently, light diffraction analysis is performed by capturing images of monochromatic light passing through companion samples undergoing the same loading conditions. The diffraction images are analyzed in the frequency domain to elucidate the stress-induced lensing effect. Correlations between terahertz and diffraction results are deduced and reported. The novel loading and characterization approaches can be utilized to investigate a broad range of polymers nondestructively and noninvasively during in situ mechanical and thermal loadings.

Nha Uyen Huynh   San Diego State University
George Youssef   San Diego State University