TY - JOUR A1 - Wang, Ningzhen A1 - van Turnhout, Jan A1 - Daniels, Robert A1 - Wu, Chao A1 - Huo, Jindong A1 - Gerhard, Reimund A1 - Sotzing, Gregory A1 - Cao, Yang T1 - Ion-boosting the charge density and piezoelectric response of ferroelectrets to significantly high levels JF - ACS applied materials & interfaces N2 - In contrast to molecular-dipole polymers, such as PVDF, ferroelectrets are a new class of flexible spatially heterogeneous piezoelectric polymers with dosed or open voids that act as deformable macro-dipoles after charging. With a spectrum of manufacturing processes being developed to engineer the heterogeneous structures, ferroelectrets are made with attractive piezoelectric properties well-suited for applications, such as pressure sensors, acoustic transducers, etc. However, the sources of the macro-dipole charges have usually been the same, microscopic dielectric barrier discharges within the voids, induced when the ferroelectrets are poled under a large electric field typically via a so-called corona poling, resulting in the separation and trapping of opposite charges into the interior walls of the voids. Such a process is inherently self-limiting, as the reverse internal field from the macro-dipoles eventually extinguishes the microdischarges, resulting in limited density of ions and not too high overall piezoelectric performance. Here, a new method to form ferroelectrets with gigantic electroactivity is proposed and demonstrated with the aid of an external ion booster. A laminate consisting of expanded polytetrafluoroethylene (ePTFE) and fluorinated-ethylene-propylene (FEP) was prefilled with bipolar ions produced externally by an ionizer and sequentially poled to force the separation of positive and negative ions into the open fibrous structure, rendering an impressive piezoelectric d(33)( )coefficient of 1600 pC/N-an improvement by a factor of 4 in comparison with the d(33) of a similar sandwich poled with nonenhanced corona poling. The (pre)filling dearly increases the ion density in the open voids significantly. The charges stored in the open-cell structure stays at a high level for at least 4 months. In addition, an all-organic nanogenerator was made from an ePTFE-based ferroelectret, with conducting poly(3,4-ethylene dioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) coated fabric electrodes. When poled with this ion-boosting process, it yielded an output power twice that of a similar sample poled in a conventional corona-only process. The doubling in output power is mainly brought about by the significantly higher charge density achieved with the aid of external booster. Furthermore, aside from the bipolar ions, extra monopolar ions can during the corona poling be blown into the open pores by using for instance a negative ionic hair dryer to produce a unipolar ePTFE-based ferroelectret with its d(33) coefficient enhanced by a factor of 3. Ion-boosting poling thus unleashes a new route to produce bipolar or unipolar open-cell ferroelectrets with highly enhanced piezoelectric response. KW - ePTFE ferroelectret KW - corona charging KW - ion boost KW - bipolar and unipolar charging KW - piezoelectric response KW - wearable energy harvester Y1 - 2022 U6 - https://doi.org/10.1021/acsami.2c12185 SN - 1944-8244 SN - 1944-8252 VL - 14 IS - 37 SP - 42705 EP - 42712 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Metzler, Ralf A1 - Rajyaguru, Ashish A1 - Berkowitz, Brian T1 - Modelling anomalous diffusion in semi-infinite disordered systems and porous media JF - New journal of physics : the open-access journal for physics N2 - For an effectively one-dimensional, semi-infinite disordered system connected to a reservoir of tracer particles kept at constant concentration, we provide the dynamics of the concentration profile. Technically, we start with the Montroll-Weiss equation of a continuous time random walk with a scale-free waiting time density. From this we pass to a formulation in terms of the fractional diffusion equation for the concentration profile C(x, t) in a semi-infinite space for the boundary condition C(0, t) = C-0, using a subordination approach. From this we deduce the tracer flux and the so-called breakthrough curve (BTC) at a given distance from the tracer source. In particular, BTCs are routinely measured in geophysical contexts but are also of interest in single-particle tracking experiments. For the "residual' BTCs, given by 1- P(x, t), we demonstrate a long-time power-law behaviour that can be compared conveniently to experimental measurements. For completeness we also derive expressions for the moments in this constant-concentration boundary condition. KW - diffusion KW - anomalous diffusion KW - breakthrough curves KW - constant boundary concentration Y1 - 2022 U6 - https://doi.org/10.1088/1367-2630/aca70c SN - 1367-2630 VL - 24 IS - 12 PB - IOP Publ. Ltd. CY - London ER - TY - JOUR A1 - Pan, Hanya A1 - Liu, Rui A1 - Gou, Tingyu A1 - Kliem, Bernhard A1 - Su, Yingna A1 - Chen, Jun A1 - Wang, Yuming T1 - Pre-eruption splitting of the double-decker structure in a solar filament JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - Solar filaments often erupt partially. Although how they split remains elusive, the splitting process has the potential of revealing the filament structure and eruption mechanism. Here we investigate the pre-eruption splitting of an apparently single filament and its subsequent partial eruption on 2012 September 27. The evolution is characterized by three stages with distinct dynamics. During the quasi-static stage, the splitting proceeds gradually for about 1.5 hr, with the upper branch rising at a few kilometers per second and displaying swirling motions about its axis. During the precursor stage that lasts for about 10 minutes, the upper branch rises at tens of kilometers per second, with a pair of conjugated dimming regions starting to develop at its footpoints; with the swirling motions turning chaotic, the axis of the upper branch whips southward, which drives an arc-shaped extreme-ultraviolet front propagating in a similar direction. During the eruption stage, the upper branch erupts with the onset of a C3.7-class two-ribbon flare, while the lower branch remains stable. Judging from the well-separated footpoints of the upper branch from those of the lower one, we suggest that the pre-eruption filament processes a double-decker structure composed of two distinct flux bundles, whose formation is associated with gradual magnetic flux cancellations and converging photospheric flows around the polarity inversion line. KW - Solar filament eruptions KW - Solar active region magnetic fields KW - Solar KW - flares KW - Solar filaments Y1 - 2021 U6 - https://doi.org/10.3847/1538-4357/abda4e SN - 0004-637X SN - 1538-4357 VL - 909 IS - 1 PB - Institute of Physics Publ. CY - London ER - TY - JOUR A1 - Campbell, Richard A1 - Kairaliyeva, Talmira A1 - Santer, Svetlana A1 - Schneck, Emanuel A1 - Miller, Reinhard T1 - Direct resolution of the interactions of a hydrocarbon gas with adsorbed surfactant monolayers at the water/air interface using neutron reflectometry JF - Colloids and interfaces N2 - We have directly resolved in the present work the interfacial composition during and after the interactions of a saturated atmosphere of oil vapor with soluble surfactant solutions at a planar water/air interface for the first time. Experiments were conducted on interactions of hexane vapor with solutions of alkyltrimethylammonium bromides and sodium dodecyl sulfate to observe the balance between cooperativity and competition of the components at the interface. In all cases, hexane adsorption was strongly enhanced by the presence of the surfactant, even at bulk surfactant concentrations four orders of magnitude below the critical micelle concentration. Cooperativity of the surfactant adsorption was observed only for sodium dodecyl sulfate at intermediate bulk concentrations, yet for all four systems, competition set in at higher concentrations, as hexane adsorption reduced the surfactant surface excess. The data fully supported the complete removal of hexane from the interface following venting of the system to remove the saturated atmosphere of oil vapor. These results help to identify future experiments that would elaborate and could explain the cooperativity of surfactant adsorption, such as on cationic surfactants with short alkyl chains and a broader series of anionic surfactants. This work holds relevance for oil recovery applications with foam, where there is a gas phase saturated with oil vapor. KW - surfactant adsorption KW - alkyltrimethylammonium bromides KW - sodium dodecyl sulfate KW - water/hexane vapor interface KW - neutron reflectometry KW - mixed adsorption layer KW - cooperative adsorption KW - competitive adsorption Y1 - 2022 U6 - https://doi.org/10.3390/colloids6040068 SN - 2504-5377 VL - 6 IS - 4 PB - MDPI CY - Basel ER - TY - JOUR A1 - Serrano-Munoz, Itziar A1 - Ulbricht, Alexander A1 - Fritsch, Tobias A1 - Mishurova, Tatiana A1 - Kromm, Arne A1 - Hofmann, Michael A1 - Wimpory, Robert C. A1 - Evans, Alexander A1 - Bruno, Giovanni T1 - Scanning manufacturing parameters determining the residual stress state in LPBF IN718 small parts JF - Advanced engineering materials N2 - The influence of scan strategy on the residual stress (RS) state of an as-built IN718 alloy produced by means of laser powder bed fusion (LPBF) is investigated. Two scan vector rotations (90 degrees-alternation and 67 degrees-rotation), each produced following two different scan vector lengths (long and short), are used to manufacture four rectangular prisms. Neutron diffraction (ND) and laboratory X-ray diffraction (XRD) techniques are used to map the bulk and surface RS state, respectively. The distortion induced upon removal from the baseplate is measured via profilometry. XRD measurements show that the two long scan vector strategies lead to higher RS when compared with the equivalent short scan vector strategies. Also, the 67 degrees-rotation strategies generate lower RS than their 90 degrees-alternation counterparts. Due to the lack of reliable stress-free d0 references, the ND results are analyzed using von Mises stress. In general, ND results show significant RS spatial non-uniformity. A comparison between ND and distortion results indicates that the RS component parallel to the building direction (Z-axis) has a predominant role in the Z-displacement. The use of a stress balance scheme allows to discuss the d0 variability along the length of the specimens, as well as examine the absolute RS state. KW - AM as-built IN718 alloy KW - distortion upon baseplate removal KW - laser powder KW - bed fusion technique KW - neutron diffraction KW - residual stress state KW - influence of scan strategy KW - stress balance conditions Y1 - 2021 U6 - https://doi.org/10.1002/adem.202100158 SN - 1438-1656 SN - 1527-2648 VL - 23 IS - 7 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Balcerek, Michal A1 - Burnecki, Krzysztof A1 - Thapa, Samudrajit A1 - Wylomanska, Agnieszka A1 - Chechkin, Aleksei T1 - Fractional Brownian motion with random Hurst exponent BT - accelerating diffusion and persistence transitions JF - Chaos : an interdisciplinary journal of nonlinear science N2 - Fractional Brownian motion, a Gaussian non-Markovian self-similar process with stationary long-correlated increments, has been identified to give rise to the anomalous diffusion behavior in a great variety of physical systems. The correlation and diffusion properties of this random motion are fully characterized by its index of self-similarity or the Hurst exponent. However, recent single-particle tracking experiments in biological cells revealed highly complicated anomalous diffusion phenomena that cannot be attributed to a class of self-similar random processes. Inspired by these observations, we here study the process that preserves the properties of the fractional Brownian motion at a single trajectory level; however, the Hurst index randomly changes from trajectory to trajectory. We provide a general mathematical framework for analytical, numerical, and statistical analysis of the fractional Brownian motion with the random Hurst exponent. The explicit formulas for probability density function, mean-squared displacement, and autocovariance function of the increments are presented for three generic distributions of the Hurst exponent, namely, two-point, uniform, and beta distributions. The important features of the process studied here are accelerating diffusion and persistence transition, which we demonstrate analytically and numerically. Y1 - 2022 U6 - https://doi.org/10.1063/5.0101913 SN - 1054-1500 SN - 1089-7682 VL - 32 IS - 9 PB - American Institute of Physics CY - Woodbury, NY ER - TY - JOUR A1 - Fornieri, Ottavio A1 - Zhang, Heshou T1 - MHD decomposition explains diffuse 𝛾-ray emission in Cygnus X JF - Physical review : D, Particles, fields, gravitation, and cosmology N2 - Cosmic-ray (CR) diffusion is the result of the interaction of such charged particles against magnetic fluctuations. These fluctuations originate from large-scale turbulence cascading toward smaller spatial scales, decomposed into three different modes, as described by magnetohydrodynamics (MHD) theory. As a consequence, the description of particle diffusion strongly depends on the model describing the injected turbulence. Moreover, the amount of energy assigned to each of the three modes is, in general, not equally divided, which implies that diffusion properties might be different from one region to another. Here, motivated by the detection of different MHD modes inside the Cygnus-X star-forming region, we study the 3D transport of CRs injected by two prominent sources within a two-zone model that represents the distribution of the modes. Then, by convolving the propagated CR distribution with the neutral gas, we are able to explain the 𝛾-ray diffuse emission in the region, observed by the Fermi-LAT and HAWC Collaborations. Such a result represents an important step in the long-standing problem of connecting the CR observables with the microphysics of particle transport. Y1 - 2022 U6 - https://doi.org/10.1103/PhysRevD.106.103015 SN - 2470-0010 SN - 2470-0029 SN - 2470-0037 VL - 106 IS - 10 PB - American Physical Society CY - Ridge, NY ER - TY - JOUR A1 - Chen, Jialin A1 - Su, Yingna A1 - Liu, Rui A1 - Kliem, Bernhard A1 - Zhang, Qingmin A1 - Ji, Haisheng A1 - Liu, Tie T1 - Partial eruption, confinement, and twist buildup and release of a double-decker filament JF - The astrophysical journal : an international review of spectroscopy and astronomical physics. N2 - We investigate the failed partial eruption of a filament system in NOAA AR 12104 on 2014 July 5, using multiwavelength EUV, magnetogram, and H alpha observations, as well as magnetic field modeling. The filament system consists of two almost co-spatial segments with different end points, both resembling a C shape. Following an ejection and a precursor flare related to flux cancellation, only the upper segment rises and then displays a prominent twisted structure, while rolling over toward its footpoints. The lower segment remains undisturbed, indicating that the system possesses a double-decker structure. The erupted segment ends up with a reverse-C shape, with material draining toward its footpoints, while losing its twist. Using the flux rope insertion method, we construct a model of the source region that qualitatively reproduces key elements of the observed evolution. At the eruption onset, the model consists of a flux rope atop a flux bundle with negligible twist, which is consistent with the observational interpretation that the filament possesses a double-decker structure. The flux rope reaches the critical height of the torus instability during its initial relaxation, while the lower flux bundle remains in stable equilibrium. The eruption terminates when the flux rope reaches a dome-shaped quasi-separatrix layer that is reminiscent of a magnetic fan surface, although no magnetic null is found. The flux rope is destroyed by reconnection with the confining overlying flux above the dome, transferring its twist in the process. Y1 - 2021 U6 - https://doi.org/10.3847/1538-4357/ac2ba1 SN - 0004-637X SN - 1538-4357 VL - 923 IS - 2 PB - Institute of Physics Publ. CY - London ER - TY - JOUR A1 - Gostkowska-Lekner, Natalia A1 - Kojda, Sandrino Danny A1 - Hoffmann, Jan-Ekkehard A1 - May, Manfred A1 - Huber, Patrick A1 - Habicht, Klaus A1 - Hofmann, Tommy T1 - Synthesis of organic-inorganic hybrids based on the conjugated polymer P3HT and mesoporous silicon JF - Microporous and mesoporous materials : zeolites, clays, carbons and related materials N2 - Organic-inorganic hybrids are a class of functional materials that combine favorable properties of their constituents to achieve an overall improved performance for a wide range of applications. This article presents the synthesis route for P3HT-porous silicon hybrids for thermoelectric applications. The conjugated polymer P3HT is incorporated into the porous silicon matrix by means of melt infiltration. Gravimetry, sorption isotherms and energy dispersive X-ray spectroscopy (EDX) mapping indicate that the organic molecules occupy more than 50% of the void space in the inorganic host. We demonstrate that subsequent diffusion-based doping of the confined polymer in a FeCl3 solution increases the electrical conductivity of the hybrid by five orders of magnitude compared to the empty porous silicon host. KW - Mesoporous silicon KW - P3HT KW - Organic-inorganic hybrid KW - Melt infiltration Y1 - 2022 U6 - https://doi.org/10.1016/j.micromeso.2022.112155 SN - 1387-1811 SN - 1873-3093 VL - 343 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Hofmann, Tommy A1 - Kojda, Sandrino Danny A1 - Haseeb, Haider A1 - Wallacher, Dirk A1 - Sobolev, Oleg A1 - Habicht, Klaus T1 - Phonons in highly-crystalline mesoporous silicon: the absence of phonon-softening upon structuring silicon on sub-10 nanometer length scales JF - Microporous and mesoporous materials : the official journal of the International Zeolite Association N2 - This article presents inelastic thermal neutron scattering experiments probing the phonon dispersion in mesoporous silicon with pores 8 nm across. Scattering studies reveal the energy-momentum relation for transverse and longitudinal phonons along the high symmetry directions , and in the Brillouin zone. The dispersion up to phonon energies of 35 meV unambiguously proves that the phonon group velocities in highly-crystalline silicon are not modified by nanostructuring down to sub-10 nanometer length scales. On these length scales, there is apparently no effect of structuring on the elastic moduli of mesoporous silicon. No evidence can be found for phonon-softening in topologically complex, geometrically disordered mesoporous silicon putting it in contrast to silicon nanotubes and nanoribbons. KW - Mesoporous silicon KW - Inelastic neutron scattering KW - Phonon dispersion KW - Phonon-softening KW - Elasticity KW - Thermoelectric material Y1 - 2021 U6 - https://doi.org/10.1016/j.micromeso.2020.110814 SN - 1387-1811 SN - 1873-3093 VL - 312 PB - Elsevier CY - Amsterdam ER -