Abstract-Experimental measurement of temperature-dependent sellmeier coefficients and thermo-optic coefficients of polymers in terahertz spectral range

Muhammad Mumtaz, M.Ahsan, Mahmood, Sabih D. Khan, M. Aslam Zia, Mushtaq Ahmed, Izhar Ahmad,

 
https://www.sciencedirect.com/science/article/pii/S0925346719301661

Terahertz time-domain spectroscopy has been used to measure the temperature-dependent absorption coefficients and refractive indices of different polymers in 0.2–1.8 THz spectral frequency. The coefficients of temperature-dependent Sellmeier equation for all these polymers have also been evaluated by statistical fitting the measured data, which will be helpful for the evaluation of dispersion properties of the material. Additionally, the thermo-optic coefficients have been evaluated to be the range of $-1.230\times {10}^{-4}$ to $-2.50\times {10}^{-4}$ K−1 for 298–373 K. This data would be helpful for the applications of polymers as THz-waveguide and other temperature sensitive devices. These results provide a temperature-dependent database of optical properties of different polymers for their efficient utilization in THz technology.

Abstract-Double-Sided Terahertz Imaging of Multilayered Glass Fiber-Reinforced Polymer

Przemyslaw Lopato


http://www.mdpi.com/2076-3417/7/7/661

Polymer matrix composites (PMC) play important roles in modern industry. Increasing the number of such structures in aerospace, construction, and automotive applications enforces continuous monitoring of their condition. Nondestructive inspection of layered composite materials is much more complicated process than evaluation of homogenous, (mostly metallic) structures. Several nondestructive methods are utilized in this case (ultrasonics, shearography, tap testing, acoustic emission, digital radiography, infrared imaging) but none of them gives full description of evaluated structures. Thus, further development of NDT techniques should be studied. A pulsed terahertz method seems to be a good candidate for layered PMC inspection. It is based on picosecond electromagnetic pulses interacting with the evaluated structure. Differences of dielectric parameters enables detection of a particular layer in a layered material. In the case of multilayered structures, only layers close to surface can be detected. The response of deeper ones is averaged because of multiple reflections. In this paper a novel inspection procedure with a data processing algorithm is introduced. It is based on a double-sided measurement, acquired signal deconvolution, and data combining. In order to verify the application of the algorithm stress-subjected glass fiber-reinforced polymer (GFRP) was evaluated. The obtained results enabled detection and detailed analysis of delaminations introduced by stress treatment and proved the applicability of the proposed algorithm.

Abstract-Investigation of Dielectric Properties of Polymers and their Discrimination Using Terahertz Time-Domain Spectroscopy with Principal Component Analysis

Muhammad Mumtaz, Ahsan Mahmood, Sabih D. Khan, M. Aslam Zia, Mushtaq Ahmed, and Izhar Ahmad

https://www.osapublishing.org/as/abstract.cfm?uri=as-71-3-456&origin=search

Polymers are among the most commonly used materials in our everyday life. They are generally transparent to terahertz (THz) radiation, but are quite difficult to differentiate using optical techniques as few or no characteristic features exist in the spectral range of <2.0 THz for small and portable radiation systems. In this work, we report experimental measurement of refractive indices and absorption coefficients of styrene acrylonitrile (SAN) and Bakelite in the spectral range of 0.2–2.0 THz for the first time. Additionally, we demonstrate that by combining principle component analysis (PCA) with THz time-domain spectroscopy one can differentiate such polymers. In this analysis, the first three principle components PC1, PC2, and PC3 depict >94% variance with a distribution of 72.45%, 11.52%, and 9.38%, respectively.

Abstract-Terahertz imaging and tomography as efficient instruments for testing polymer additive manufacturing objects

J. B. Perraud, A. F. Obaton, J. Bou-Sleiman, B. Recur, H. Balacey, F. Darracq, J. P. Guillet, and P. Mounaix
https://www.osapublishing.org/ao/abstract.cfm?uri=ao-55-13-3462

Additive manufacturing (AM) technology is not only used to make 3D objects but also for rapid prototyping. In industry and laboratories, quality controls for these objects are necessary though difficult to implement compared to classical methods of fabrication because the layer-by-layer printing allows for very complex object manufacturing that is unachievable with standard tools. Furthermore, AM can induce unknown or unexpected defects. Consequently, we demonstrate terahertz (THz) imaging as an innovative method for 2D inspection of polymer materials. Moreover, THz tomography may be considered as an alternative to x-ray tomography and cheaper 3D imaging for routine control. This paper proposes an experimental study of 3D polymer objects obtained by additive manufacturing techniques. This approach allows us to characterize defects and to control dimensions by volumetric measurements on 3D data reconstructed by tomography.

© 2016 Optical Society of America

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Superlattices Patterned by Polymers

https://www-als.lbl.gov/index.php/science-highlights/science-briefs/1088

Scientists have shown that self-assembled superlattices, made up of nanoparticles with polymer chains grafted onto their surfaces (“hairy nanoparticles,” or polymer “brushes”), can be tailored to exhibit desired characteristics for applications ranging from nano- to biotechnology. Such multicomponent polymer-nanoparticle composites represent an important class of materials that exhibit emergent properties arising from their mesoscale structure.

The use of extended polymeric ligands on the nanoparticles’ surfaces (as opposed to the shorter ligands native to the nanoparticles) offers distinct advantages, as they allow for precise tuning of the effective size of the composite particles and of the “softness” of the interactions between them through changes in the polymer’s molecular weight, chemical nature, architecture, stiffness, and solvent.

With the help of grazing-incidence small-angle x-ray scattering (GISAXS) measurements at Beamline 7.3.3, the scientists developed a set of modular building blocks—the aforementioned polymer-grafted nanocrystals—in which the inorganic core and the organic ligand shell play complementary and equally important roles in dictating the structure and function of the final assembled phase.

They demonstrated the formation of a diverse array of self-assembled binary superlattices with both two- and three-dimensional ordering. The study will open up new and exciting opportunities for the bottom-up design of functional inorganic-organic hybrid materials with controlled nanoscale interfaces and mesoscale ordering.

Scanning electron microscopy image (left) and GISAXS pattern of AB-type two-dimensional superlattices (right). 
Left inset: Schematic illustration of nanoparticles end-grafted with polymer brushes.

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Work performed at Beamline 7.3.3.

Xingchen Ye, Chenhui Zhu, Peter Ercius, Shilpa N. Raja, BoH, Matthew R. Jones, Matthew R. Hauwiller, Yi Liu, Ting Xu, and A. Paul Alivisatos, “Structural diversity in binary superlattices self-assembled from polymer-grafted nanocrystals," Nature Communications 6, 10052 (2015).

Abstract- Structure-Sensitive Maxima in the Absorption Spectra of Polymers in the Terahertz Frequency Range

M. S. Kitai, 

M. M. Nazarov, 

D. A. Sapozhnikov, 

V. I. Bykov, 

M. V. Bermeshev, 

S. A. Bulgakova, 

B. F. Shklyaruk

http://link.springer.com/article/10.1007/s11141-015-9572-7
The basic sizes characterizing the morphology of a few practically important synthetic organic polymers in the glassy and viscoelastic states are confronted with the maxima of the absorption spectra in the terahertz frequency range. These sizes are determined using the X-ray diffraction technique. The absorption spectra of these polymers have been measured by the method of terahertz time-domain spectroscopy in the temperature range from helium to room temperatures.