10 research outputs found
Dielectric properties of 3D printed polylactic acid
3D printers constitute a fast-growing worldwide market. These printers are often employed in research and development fields related to engineering or architecture, especially for structural components or rapid prototyping. Recently, there is enormous progress in available materials for enhanced printing systems that allow additive manufacturing of complex functional products, like batteries or electronics. The polymer polylactic acid (PLA) plays an important role in fused filament fabrication, a technique used for commercially available low-budget 3D printers. This printing technology is an economical tool for the development of functional components or cases for electronics, for example, for lab purposes. Here we investigate if the material properties of “as-printed” PLA, which was fabricated by a commercially available 3D printer, are suitable to be used in electrical measurement setups or even as a functional material itself in electronic devices. For this reason, we conduct differential scanning calorimetry measurements and a thorough temperature and frequency-dependent analysis of its dielectric properties. These results are compared to partially crystalline and completely amorphous PLA, indicating that the dielectric properties of “as-printed” PLA are similar to the latter. Finally, we demonstrate that the conductivity of PLA can be enhanced by mixing it with the ionic liquid “trihexyl tetradecyl phosphonium decanoate.” This provides a route to tailor PLA for complex functional products produced by an economical fused filament fabrication
Tetramethylbenzidine-TetrafluoroTCNQ: A narrow-gap semiconducting salt with room temperature relaxor ferroelectric behavior
We present an extension and revision of the spectroscopic and structural data
of the mixed stack charge transfer (CT) crystal
3,3,5,5-tetramethylbenzidine--tetrafluoro-tetracyanoquinodimethane
(TMB-TCNQF4), associated with new electric and dielectric measurements.
Refinement of syncrotron structural data at low temperature has led to revise
the previously reported [Phys. Rev. Mat. 2, 024602 (2018)] structure.
The revised structure is , with two dimerized stacks per unit cell, and
is consistent with the vibrational data. However, polarized Raman data in the
low-frequency region also indicate that by increasing temperature above 200 K
the structure presents an increasing degree of disorder mainly along the stack
axis. X-ray diffraction data at room temperature have confirmed that the
correct structure is -- no phase transitions -- but did not allow to
definitely substantiate the presence of disorder. On the other hand, dielectric
measurement have evidenced a typical relaxor ferroelectric behavior already at
room temperature, with a peak in real part of dielectric constant
around 200 K and 0.1 Hz. The relaxor behavior is explained
in terms of the presence of spin solitons separating domains of opposite
polarity that yield to ferroelectric nanodomains. TMB-TCNQF4 is confirmed to be
a narrow gap band semiconductor ( eV) with room temperature
conductivity of cm.Comment: 21 pages, including the Supporting Information in the same file.
Version 3 updates the x-ray structural data at room temperatur
Ionische Flüssigkeiten für zukünftige Energiespeicher - eine umfassende dielektrische Charakterisierung
Ionische Flüssigkeiten für zukünftige Energiespeicher - eine umfassende dielektrische Charakterisierung
Ionische Flüssigkeiten für zukünftige Energiespeicher - eine umfassende dielektrische Charakterisierung
Supercooled water confined in a metal-organic framework
Within the so-called "no-man's land" between about 150 and 235 K,
crystallization of bulk water is inevitable. The glasslike freezing and a
liquid-to-liquid transition of water, predicted to occur in this region, can be
investigated by confining water in nanometer-sized pores. Here we report the
molecular dynamics of water within the pores of a metal-organic framework using
dielectric spectroscopy. The detected temperature-dependent dynamics of
supercooled water matches that of bulk water as reported outside the borders of
the no-man's land. In confinement, a different type of water is formed,
nevertheless still undergoing a glass transition with considerable molecular
cooperativity. Two different length scales seem to exist in water: A smaller
one, of the order of 2 nm, being the cooperativity length scale governing
glassy freezing, and a larger one (> 2 nm), characterizing the minimum size of
the hydrogen-bonded network needed to create "real" water with its unique
dynamic propertiesComment: This is a pre-print of an article published in "Communication
Physics". The final authenticated version is available online at:
https://doi.org/10.1038/s42005-020-0363-x
Spin probe dynamics of n-hexadecane in confined geometry
A combined study of the rotational dynamics of the stable free radical 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and the phase behavior of n-hexadecane (n-HXD) in the bulk and the confined states in a series of silica gels (SG) by means of ESR and DSC is presented. A slow to fast motion transition of the spin probe TEMPO in the bulk n-HXD occurs at T50 G,bulk ≪ Tm,bulk, i.e., well below the melting temperature due to its trapping and localized mobility in the interlamellar gap of the crystallites [J. Bartoš, H. Švajdlenková, M. Zaleski, M. Edelmann, M. Lukešová, Physica B 430, 99 (2013)]. On the other hand, the dynamics of the TEMPO in the confined systems is strongly slowing down with T50 G (Dpore) >Tm(Dpore) and slightly increases with the pore size Dpore = 60, 100 and 300 Å of the SG’s. At the same time, both the corresponding melting temperature, Tm (Dpore), and melting enthalpy, ΔHm (Dpore), decrease with Dpore together with the mutual anti-correlation between T50 G and Tm as a function of the inverse of pore diameter, 1/Dpore. Moreover, the dynamic heterogeneity of the TEMPO in the confined state below T50 G (Dpore) is closely related to the phase transformation. The strong slowing down of the spin probe motion likely results from its preferential localization at the interface layer of the matrix pore due to specific interaction of TEMPO molecules with the polar silanol groups of the SG matrix. This is supported by special study on a series of the variously filled n-HXD/SG systems, other similar experimental findings as well as by theoretical spectral argument
Tetramethylbenzidine-TetrafluoroTCNQ (TMB-TCNQF(4)) : a narrow-gap semiconducting salt with room-temperature relaxor ferroelectric behavior
Single-Crystal to Single-Crystal Transformation of a Nonporous Fe(II) Metal–Organic Framework into a Porous Metal–Organic Framework via a Solid-State Reaction
We
report the synthesis of an air-stable nonporous coordination compound
based on iron(II) centers, formate anions, and a 4,4′-bipyrazole
(H<sub>2</sub>BPZ) ligand. Upon thermal treatment, a porous metal–organic
framework (MOF) formed due to decomposition of the incorporated formate
anions. This decomposition step and the following structural changes
constituted a single-crystal to single-crystal transformation. The
resulting [Fe(BPZ)] framework contained tetrahedrally coordinated
iron(II) metal centers. The framework was sensitive toward oxidation
by molecular oxygen even at temperatures of 183 K, as followed by
oxygen sorption measurements and a color change from colorless to
metallic black. The semiconductor properties of the oxidized material
were studied by diffuse reflectance UV/vis/NIR spectroscopy and dielectric
spectroscopy