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Understanding the interactions of the crystalline and the amorphous domains in semi-crystalline polymers, such as HDPE or PVDF, is a subject of ongoing research. Here, we apply terahertz time-domain spectroscopy to study the impact of the glass transition taking place in the amorphous phase on lattice modes associated with the crystalline domains.
We investigate the THz properties of nematic liquid crystals as a function of temperature. In particular we focus on the refractive index the absorption and the birefringence. From the measured data, molecular properties (polarizability and S parameter) are deduced. We discuss the impact of the molecular chain length on the polarizability.
Decreasing the temperature leads to a blue shift of the B1u lattice mode in different types of polyethylene, which can be observed using terahertz time-domain spectroscopy. Moreover, the frequency shift reveals the glass transition of high-density polyethylene due to the semi-crystalline nature in this polymer. In addition, morphological factors on the B1u lattice mode of LDPE, LLDPE, and HDPE are...
We present a time domain and a frequency domain based algorithm for the analysis of spectroscopic terahertz data. The thickness information as well as the frequency dependent complex material parameters are extracted. Both methods can evaluate data obtained from measurements on sub-100mum thick samples, even in case of overlapping Fabry Perot echoes in the time domain. While the frequency domain approach...
We investigate various composite systems in the terahertz frequency regime and apply different effective medium theories to model their dielectric response. A broad variety of composites is considered, ranging from polymeric compound mixtures to biological samples. For each case, the effective medium theory of choice is illuminated in detail.
The glass transition temperature Tg of polymers is identified by terahertz time-domain spectroscopy (TDS). The thermo-quasi-optic coefficient noticeably changes in the region of the glass transition. THz TDS can thus serve as a non-destructive and non-contact technique for polymer analysis.
We investigate the temperature dependent absorption characteristics of polyamides (PA) in the terahertz frequency range. The absorption spectra can be explained by inter-molecular bonding mechanisms. Experimental data is obtained by terahertz time-domain spectroscopy (THzTDS) on injection-molded specimens as well as on molten polyamides at different temperatures. The THzTDS data is compared to FTIR...
We present two fiber-coupled terahertz (THz) time-domain transceiver heads that are well suited for zero degree reflection measurements and allow for flexible handling. One consists of only one photoconductive switch that is capable of emitting and detecting at the same time and the other operates with two antennas and a beam splitter made from a polypropylene-titanium (PP-TiO2) compound.
We demonstrate the use of a fiber stretcher as an optical delay line in a fiber-coupled THz spectrometer. No measurable dispersion effects occur when extending the fiber. Measurements of the terahertz pulses at a stretching frequency of 20 Hz show the great potential of such a device for future all-fiber terahertz systems.
We present non-destructive and contactless inline measurements on the molten polymer polypropylene and on the polymeric compound polypropylene-CaCO3 carried out with a THz spectrometer. The effect of temperature and pressure on the THz properties of the molten polymeric material is investigated. Additionally, we analyze the additive content of the compound during the extrusion processing and compare...
Using THz time-domain and FTIR spectroscopy we measure the far-infrared absorption spectra of various biomolecular crystals with different numbers of hydrogen bonds of different strengths. The experimental data are compared to density functional theory calculations.
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