skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Ex situ Spectroscopic Characterization of Residual Effects of Thermomechanical Loading on Polyurea
Abstract The residual effect of thermally and mechanically loaded polyurea samples was investigated in this study using terahertz time-domain spectroscopy (THz-TDS). Samples of different thicknesses were submerged in liquid nitrogen and allowed to reach cryogenic isothermal conditions while another set of samples were extracted from quasi-statically loaded strips. All samples were interrogated using THz-TDS since terahertz waves exhibit non-ionizing, nondestructive interactions with polymers. The time-domain terahertz signals were used to extract the optical and electrical properties as a function of sample thickness and loading conditions. The residual effect was prominent in the mechanically loaded samples compared to a nearly negligible presence in thermally loaded polyurea. On average, the results of the thermally loaded samples were subtle when compared to the virgin samples, whereas samples that were mechanically stretched showed a considerable difference in the characteristics of the time-domain signals. For example, the peak amplitude in the time-domain signal of the stretched thick sample showed a 9% difference from that of the virgin sample, whereas the thermally loaded sample saw only a 4.9% difference. Spectral analysis reported the frequency-dependent, complex refractive index of virgin and loaded polyurea as a function of thickness and spectral peaks associated with fundamental vibrational modes of the polyurea structure. The disappearance of three spectral peaks, 0.56 THz, 0.76 THz, and 0.95 THz, elucidated the residual effect of the mechanically loaded samples. In general, terahertz spectroscopy was shown to be a promising tool for future in situ and in operando investigations of field-dependent polymer responses.  more » « less
Award ID(s):
1925539
PAR ID:
10337476
Author(s) / Creator(s):
;
Date Published:
Journal Name:
Journal of Engineering Materials and Technology
Volume:
144
Issue:
3
ISSN:
0094-4289
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; (, Macromolecular Materials and Engineering)
    Abstract The core of this research is separated into three domains, the ultrahigh strain rate response of elastomeric polymers, laser‐induced shock waves , and terahertz time‐domain spectroscopy (THz‐TDS). Elastomers, e.g., polyurea, constitute an advance class of materials suitable for many applications, specifically in high impact loading scenarios, thus, a laser‐induced shock wave (LSW) experimental technique is used to investigate the mechanical response of shock‐loaded polyurea. LSW can submit samples to a strain rate exceeding 106s−1at low strains, enabling determination of material intrinsic failure modes. The large deformation induced during shock loading may alter the macromolecule structure, which can only be detected spectroscopically. Therefore, this research incorporated terahertz bulk spectroscopy to detect and report molecular conformational changes. Microscopy techniques were also used to elucidate changes in the microscale properties, morphology, and topography. The interpretation of the results explicated brittle failure in terms of partial and total spallation and, remarkably, ductile failure leading to plastic deformation, including plastic bulging and adiabatic shearing, not previously associated with LSW technique. Furthermore, spectral changes found in the terahertz regime substantiated the validity of terahertz spectroscopy in elucidating the underlying mechanism associated with the impact mitigating properties of dynamically loaded polyurea. 
    more » « less
  2. (, Digest IEEE Antennas and Propagation Society International Symposium)
    IEEE (Ed.)
    This paper presents fabrication and experimental measurements of broadband terahertz (THz) photoconductive antennas (PCAs), based on the conventional low temperature gallium arsenide (LT-GaAs) material. Various antenna electrode geometries, that were previously designed through computer simulations, are fabricated using the electron beam lithography (EBL). The generated time domain pulse is measured using a time domain spectroscopy system (TDS). The bandwidth of each emitting device is obtained using the fast Fourier transform of the generated electric field pulse. 
    more » « less
  3. (, IEEE Antennas and Propagation Symposium)
    null (Ed.)
    This paper presents the signal generation measurements of LT-GaAs photoconductive antenna (PCA) emitters. These measurements were developed in an open-bench time-domain spectroscopy (TDS) system. The main challenges presented here are associated with the alignment of the PCA devices and the location of the terahertz (THz) pulse with respect to the optical delay in the system. The position of the slow delay line was crucial for the location of the THz pulse, which helped in the correct alignment process of the emitter and detector devices. 
    more » « less
  4. ; (, Antennas and Propagation Society International Symposium)
    This paper presents the signal generation measurements of LT-GaAs photoconductive antenna (PCA) emitters. These measurements were developed in an open-bench time-domain spectroscopy (TDS) system. The main challenges presented here are associated with the alignment of the PCA devices and the location of the terahertz (THz) pulse with respect to the optical delay in the system. The position of the slow delay line was crucial for the location of the THz pulse, which helped in the correct alignment process of the emitter and detector devices. 
    more » « less
  5. ; ; (, Journal of Physics: Condensed Matter)
    Abstract Two-dimensional (2D) van der Waals materials are shaping the landscape of next-generation devices, offering significant technological value thanks to their unique, tunable, and layer-dependent electronic and optoelectronic properties. Time-domain spectroscopic techniques at terahertz (THz) frequencies offer noninvasive, contact-free methods for characterizing the dynamics of carriers in 2D materials. They also pave the path toward the applications of 2D materials in detection, imaging, manufacturing, and communication within the increasingly important THz frequency range. In this paper, we overview the synthesis of 2D materials and the prominent THz spectroscopy techniques: THz time-domain spectroscopy (THz-TDS), optical pump THz probe (OPTP) technique, and optical pump--probe (OPP) THz spectroscopy. Through a coalescence of experimental findings, numerical simulation, and theoretical analysis, we present the current understanding of the rich ultrafast physics of technologically significant 2D materials: graphene, transition metal dichalcogenides, MXenes, perovskites, topological 2D materials, and 2D heterostructures. Finally, we offer a perspective on the role of THz characterization in guiding future research and in the quest for ideal 2D materials for new applications. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email