Non-aligned Samples Research Articles

Characterisation of cement loaded with magnetically aligned nano-magnetite

In this study, the effect on the compressive strength of cement with the addition of 1–5 wt% nano-magnetite particles (nano-Fe3O4) is identified at the age of 7 days and 28 days of curing. In addition, an approach of aligning these nano-magnetite particles within cement using an external magnetic field is presented, where the orientation of nano-magnetite particles is aligned parallel to the compressive load. The effect of the compressive strength on cement mortar with the aligned nano-magnetite particles is compared with the non-aligned samples. Both aligned and non-aligned samples show positive effects on the compressive strengths as compared to the control samples, where the cement mortar with aligned nano-magnetite shows significant improvement on compressive strength up to 21%. This study also shows that the addition of 3 wt% nano-magnetite particles to cement mortar is the optimal amount to achieve maximum enhancement of compressive strengths.

Magnetic filler alignment of single graphene nanoplatelets modified by Fe3O4 to improve the thermal conductivity of the epoxy composite

In this paper, to improve the thermal conductivity of polymer composites, the epoxy matrix has been filled with single graphene nanoplatelets (SGNPs) modified by Fe3O4 magnetic nanoparticles. Fe3O4 modified graphene nanoplatelets were aligned by the magnetic field tunnel method in the epoxy matrix. The highest alignment and controlled orientation of the nanoplatelets were achieved in different composite samples. FT-IR and TEM tests were used to investigate the structure and characterization of SGNP@Fe3O4 synthesized nanoparticles. A constant intensity magnetic field at different times was used to control the nanoplatelets' orientation in the epoxy matrix. This controlled orientation and high alignment of the fillers lead to an increase in the thermal conductivity of the composite. The thermal conductivity of the EP/SGNP @Fe3O4 composite showed a 309% increase in high alignment compared to the non-aligned samples.

Residual Magnetic Moment Influences the Features of Fe3s XPS Spectrum: A Case Study

Background: Fe 3sXPS spectrum exhibits doublet peak instead of predicted singlet peak based on spin-orbit coupling theory. This anomalous behavior is considered to be of magnetic origin. However, the effect of residual magnetic moment on the features of Fe3s doublet peak is not understood fully. Objective: This study aims to verify the effect of residual magnetic moment on the spectral features of Fe3s XPS spectrum of magnetic material. Method: As a case study, we have carried out a high-temperature XPS study of the Fe 3s spectrum of magnetic domain aligned (MDA) sample with composition composed of SrFe10.8Al1.2O19. In addition, the XPS data have been compared with the data acquired at different temperatures of magnetic domain non-aligned (MDNA) sample. Results: The results show that the majority peak intensity and minority peak width of Fe 3s spectrum of MDA are smaller than those of the MDNA sample, and they increase systematically with increasing temperature. However, it is noted that the features of Fe3s spectrum of both MDA and MDNA samples completely overlap near and above the Curie temperature, Tc ~ 670K. Discussion: The residual magnetic flux in the MDA sample alters the interaction between 3s electrons and valence 3d spin. In addition, the presence of residual magnetic moment leads to deviation of the escaped electrons from their path, therefore the majority peak intensity of MDA sample becomes smaller than the MDNA sample at below the Curie temperature. Consequently, the spectral features of MDA samples are different than the MDNA samples at below the Curie temperature. Conclusion: The analysis of XPS data suggests that the residual magnetic moment influences the spectral features of the Fe3s spectrum. These results provide evidence that it is important to consider the contribution of the residual magnetic moment while deriving information from the Fe 3s XPS spectrum of the MDA sample.

Two-Step Affine Transformation Prediction for Visual Object Tracking

The main drawback of correlation filter scheme is that it can only predict translation of the object, ignoring the other affine transformations such as rotation, aspect ratio change, and scale change. This paper tries to address this problem by a two-step affine transformation prediction method. The first step is to predict coarse target translation by the correlation filter model with adaptive model update rate generation. Compared with fixed update rate in existing correlation filter based trackers, the presented method generates the update rate by Long Short-Term Memory model with inputs of historical target templates. The second step maps well-designed features to affine transformation parameters. The designed features contain the information of affine transformation which makes the learning of non-linear mapping function possible. The training samples for on-line filter model update are transformed to the same pose, and they help the learnt filter to represent the object better than non-aligned samples. The proposed network is trained from end to end and achieves competitive performance when comparing with state-of-the-arts trackers on four benchmarks, OTB100, UAV123, VOT2018, and VOT2020.

All-Optically Controllable Photonic Crystals Based on Chiral-Azobenzene-Doped Blue Phase Liquid Crystals

In this study, the all-optical control properties of photonic crystals based on self-assembled chiral-azobenzene-doped blue phase liquid crystals (CA-BPLCs) were investigated. The difference in the photothermal characteristics of CA-BPLCs with and without homogeneous surface alignment was discussed. Results revealed that surface alignment could induce more uniform and diverse blue phase (BP) structures, including BPII, BPI, and BPS-like phases during cooling. Consequently, the temperature range of BP was wider than that of the sample without surface alignment. All-optical control experiments with light illumination were then performed on the aligned or nonaligned CA-BPLC samples. During continuous irradiation with light beams at wavelengths of 405 and 450 nm, CA dopants underwent trans→cis and cis→trans back photoisomerizations, respectively. These processes promoted isothermal phase transition and wavelength shifting, which further enabled the all-optical control of the CA-BPLC samples. Various optical control modes of BPLC could be achieved through phase change and wavelength shifting by appropriately selecting the working temperature and surface treatment of BPLC. This study could be further used as a basis for developing photoswitchable and tunable BPLC photonic devices, such as light-controllable gratings, filters, mirrors, and lasers.

The Effects of Magnetic Field Alignment on Lithium Ion Transport in a Polymer Electrolyte Membrane with Lamellar Morphology.

The transport properties of block copolymer-derived polymer electrolyte membranes (PEMs) are sensitive to microstructural disorder originating in the randomly oriented microdomains produced during uncontrolled self-assembly by microphase separation. This microstructural disorder can negatively impact performance due to the presence of conductivity-impeding grain boundaries and the resulting tortuosity of transport pathways. We use magnetic fields to control the orientational order of Li-doped lamellar polyethylene oxide (PEO) microdomains in a liquid crystalline diblock copolymer over large length scales (>3 mm). Microdomain alignment results in an increase in the conductivity of the membrane, but the improvement relative to non-aligned samples is modest, and limited to roughly 50% in the best cases. This limited increase is in stark contrast to the order of magnitude improvement observed for magnetically aligned cylindrical microdomains of PEO. Further, the temperature dependence of the conductivity of lamellar microdomains is seemingly insensitive to the order-disorder phase transition, again in marked contrast to the behavior of cylinder-forming materials. The data are confronted with theoretical predictions of the microstructural model developed by Sax and Ottino. The disparity between the conductivity enhancements obtained by domain alignment of cylindrical and lamellar systems is rationalized in terms of the comparative ease of percolation due to the intersection of randomly oriented lamellar domains (2D sheets) versus the quasi-1D cylindrical domains. These results have important implications for the development of methods to maximize PEM conductivity in electrochemical devices, including batteries.

Arrangement at the nanoscale: Effect on magnetic particle hyperthermia.

In this work, we present the arrangement of Fe3O4 magnetic nanoparticles into 3D linear chains and its effect on magnetic particle hyperthermia efficiency. The alignment has been performed under a 40 mT magnetic field in an agarose gel matrix. Two different sizes of magnetite nanoparticles, 10 and 40 nm, have been examined, exhibiting room temperature superparamagnetic and ferromagnetic behavior, in terms of DC magnetic field, respectively. The chain formation is experimentally visualized by scanning electron microscopy images. A molecular Dynamics anisotropic diffusion model that outlines the role of intrinsic particle properties and inter-particle distances on dipolar interactions has been used to simulate the chain formation process. The anisotropic character of the aligned samples is also reflected to ferromagnetic resonance and static magnetometry measurements. Compared to the non-aligned samples, magnetically aligned ones present enhanced heating efficiency increasing specific loss power value by a factor of two. Dipolar interactions are responsible for the chain formation of controllable density and thickness inducing shape anisotropy, which in turn enhances magnetic particle hyperthermia efficiency.

Structural, magnetic and electromagnetic properties of SrFe12O19 ferrite with particles aligned in a magnetic field

Plate-like hexagonal SrFe12O19 particles were synthesized by hydrothermal process. The as-synthesized particles were dispersed evenly in epoxy resin and then took root in the curing epoxy matrix under a uniform magnetic field. The microstructures, morphologies, magnetic and electromagnetic properties of the composites were studied. The plate-like particles were arranged with the plates perpendicular to the field direction. This demonstrated that the easy axis of the particle was perpendicular to the plate. There were obvious differences in remanent magnetization (Mr) among the aligned sample with the plates parallel to the testing direction (parallel sample), the aligned one with the plates perpendicular to the testing direction (perpendicular sample), and the nonaligned one (nonaligned sample). The perpendicular sample was better at storage capacity of electric and magnetic energy than the others. This indicated both the polarization and domain wall displacement were different between the easy axis direction and the hard axis one. The parallel sample caused maximum dielectric loss and the perpendicular sample caused minimum dielectric loss in the frequency range 2–12 GHz and 14.4–18 GHz, while it was reverse in the frequency range 12–14.4 GHz. The nonaligned sample caused maximum magnetic loss in the low frequency range, while the aligned samples were not superior at magnetic loss in the whole frequency range.

Magnetization reversal behavior of SmCo6.6Nb0.4 nanoflakes prepared by surfactant-assisted ball milling

In this paper, the recoil loops of SmCo6.6Nb0.4 nanoflakes prepared by the surfactant-assisted high energy ball milling (SA-HEBM) were systematically studied. The recoil loop openness was observed in both the aligned and non-aligned samples. Reversible and irreversible portions of the demagnetization process derived from the recoil loop were also investigated. For both the aligned and non-aligned samples, reversible portion (▵mrev) is too small to determine the coercivity. Irreversible portion (▵mirrev) shows similar tendency, i.e. increasing slowly at low reverse field and then growing up rapidly after a critical field (nucleation field Hno). The demagnetization process can be described as following: the reversible demagnetization is dominant when the applied reverse field is lower than 8 kOe, under which the irreversible nucleation also occurs. The reverse domain walls are pinned by the grain boundaries until the reverse field is larger than 8 kOe. With increasing field, the pinning effects are weakened and the rapid reversible demagnetization starts. Finally, the demagnetization process is accomplished. The values of ΔM in the Henkel plots are totally opposite for the aligned and non-aligned SmCo6.6Nb0.4 nanoflakes.

Scalable fabrication of polymer membranes with vertically aligned 1 nm pores by magnetic field directed self-assembly.

There is long-standing interest in developing membranes possessing uniform pores with dimensions in the range of 1 nm and physical continuity in the macroscopic transport direction to meet the needs of challenging small molecule and ionic separations. Here we report facile, scalabe fabrication of polymer membranes with vertically (i.e., along the through-plane direction) aligned 1 nm pores by magnetic-field alignment and subsequent cross-linking of a liquid crystalline mesophase. We utilize a wedge-shaped amphiphilic species as the building block of a thermotropic columnar mesophase with 1 nm ionic nanochannels, and leverage the magnetic anisotropy of the amphiphile to control the alignment of these pores with a magnetic field. In situ X-ray scattering and subsequent optical microscopy reveal the formation of highly ordered nanostructured mesophases and cross-linked polymer films with orientational order parameters of ca. 0.95. High-resolution transmission electron microscopy (TEM) imaging provides direct visualization of long-range persistence of vertically aligned, hexagonally packed nanopores in unprecedented detail, demonstrating high-fidelity retention of structure and alignment after photo-cross-linking. Ionic conductivity measurements on the aligned membranes show a remarkable 85-fold enhancement of conductivity over nonaligned samples. These results provide a path to achieving the large area control of morphology and related enhancement of properties required for high-performance membranes and other applications.

Photopyroelectric Calorimetry Study of the Smectic A-Hexatic B Transition in Single Homeotropic Domain 65OBC Liquid Crystal Samples

The work deals with the investigations of the smecticA-hexaticB phase transition in n-hexyl-4′-n-pentyloxybiphenyl-4-carboxylate liquid crystal compound in a single domain homeotropic sample and in a nonaligned sample. The specific heat, the thermal diffusivity, and the enthalpy exchange were monitored over the transition and, at the same time, polarization microscopy observations could be carried out. The transition during the first cooling run was found to be accompanied by a considerably larger defect annealing in the non aligned sample than in the homeotropic one.

Study of the smecticA–hexaticB phase transition in homeotropic single domain samples of 65OBC liquid crystal by photopyroelectric calorimetry

The smecticA-hexaticB phase transition was studied in a homeotropic single domain sample and in a non-aligned sample of n-hexyl-4'-n-pentyloxybiphenyl-4-carboxylate liquid crystal compound to probe the effect of different amount of defects on the phase transition. The specific heat, the thermal diffusivity and the enthalpy exchange were monitored over the transition and, at the same time, polarization microscopy observations could be carried out. The transition during the first cooling run was found to be accompanied by a considerably larger defect annealing in the non-aligned sample than in the homeotropic one, but the critical behaviour of the specific heat remained substantially the same.

Fabrication of Aligned-Carbon-Nanotube-Composite Paper with High and Anisotropic Conductivity

A functional carbon-nanotube (CNT)-composite paper is described in which the CNTs are aligned. This “aligned-CNT composite paper” is a flexible composite material that has CNT functionality (e.g., electrical conductivity) despite being a paper. An advanced fabrication method was developed to overcome the problem of previous CNT-composite papers, that is, reduced conductivity due to random CNT alignment. Aligning the CNTs by using an alternating current (AC) field was hypothesized to increase the electrical conductivity and give the paper an anisotropic characteristic. Experimental results showed that a nonionic surfactant was not suitable as a CNT dispersant for fabricating aligned-CNT composite paper and that catechin with its six-membered rings and hydrophilic groups was suitable. Observation by scanning electron microscopy of samples prepared using catechin showed that the CNTs were aligned in the direction of the AC field on the paper fibers. Measurement of the electric conductivity showed that the surface resistance was different between the direction of the aligned CNTs (high conductivity) and that of verticality (low). The conductivity of the aligned-CNT-composite paper samples was higher than that of nonaligned samples. This unique and functional paper, which has high and anisotropic conductivity, is applicable to a conductive material to control the direction of current.

Effect of aligning magnetic field on the magnetic and calorimetric properties of ferrimagnetic bioactive glass ceramics for the hyperthermia treatment of cancer

The magnetic and heat generating properties of the ferrimagnetic zinc-ferrite containing bioactive glass ceramics have been enhanced by aligning magnetic field, without any compositional or micro-structural changes in the material. The glass ceramics were heated to 600 °C and cooled in an aligning magnetic field of 1 T. Magnetically aligned samples were compared with the non-aligned samples. VSM measurements taken at 500 Oe showed that coercive force, remanance magnetization and hysteresis area increased for the aligned samples. This occurred because the aligning magnetic field setup an easy axis for the magnetic domains. After cooling, the domains were trapped and became stable along the direction of aligning field. Now stronger magnetic field was required to turn the domains away from their aligned positions. Thus magnetic properties were enhanced by the aligning magnetic field and it led to enhance the heat generation under magnetic induction furnace operating at 500 Oe and 60 kHz for 2 min. Data showed that maximum specific power loss and temperature increase after 2 min were 4.4 W/g and 6.3 °C respectively for the aligned sample of maximum zinc-ferrite crystalline content having pseudo single domain crystalline structure. The glass ceramics were immersed in simulated body fluid over weeks. FTIR, SEM and EDX results indicated the growth of precipitated Hydroxyapatite suggesting the bioactivity of the materials.

Study of an anisotropic ferrimagnetic bioactive glass ceramic for cancer treatment

For the hyperthermia therapy of cancer, ferrimagnetic glass ceramics are a potential candidate. Ferrimagnetic zinc-ferrite-containing bioactive glass ceramics were prepared by quenching the glass ceramics from sintering temperature. Then the samples were heated to 600°C and cooled in an aligning magnetic field of 1 Tesla to cause anisotropy. The magnetically aligned samples were compared with non-aligned samples. Vibrating sample magnetometry measurements at 10 kOe showed that the magnetic properties were enhanced by the aligning magnetic field and it led to an enhancement of the magnetic heat generation under a magnetic induction furnace operating at 500 Oe and 400 kHz for 2 min. Data showed that the maximum specific power loss and temperature increase after 2 min were 31.5 W/g and 45°C, respectively, for the aligned sample of maximum zinc-ferrite crystalline content. The glass ceramics were immersed in simulated body fluid for 3 weeks. X-ray diffraction and Fourier transform infrared and atomic absorption spectroscopy results indicated the growth of precipitated hydroxyapatite, suggesting that the ferrimagnetic glass ceramics were bioactive and could bond to living tissues in physiological environment.

Patterns of Diacetylene-Containing Peptide Amphiphiles Using Polarization Holography

The polarization dependence of a diacetylene polymerization was studied. For this purpose, peptide amphiphile fibers with a diacetylene moiety, which could only polymerize in the direction of the fiber, were employed. If nonaligned samples were illuminated with polarized light, only the fibers parallel to the polarization direction of the light were polymerized. With magnetically aligned fibers, spatially selective polymerization was accomplished using polarization holography.

The Functional Curli Amyloid Is Not Based on In-register Parallel β-Sheet Structure

The extracellular curli proteins of Enterobacteriaceae form fibrous structures that are involved in biofilm formation and adhesion to host cells. These curli fibrils are considered a functional amyloid because they are not a consequence of misfolding, but they have many of the properties of protein amyloid. We confirm that fibrils formed by CsgA and CsgB, the primary curli proteins of Escherichia coli, possess many of the hallmarks typical of amyloid. Moreover we demonstrate that curli fibrils possess the cross-beta structure that distinguishes protein amyloid. However, solid state NMR experiments indicate that curli structure is not based on an in-register parallel beta-sheet architecture, which is common to many human disease-associated amyloids and the yeast prion amyloids. Solid state NMR and electron microscopy data are consistent with a beta-helix-like structure but are not sufficient to establish such a structure definitively.

In Situ Synthesis and Alignment of Au Nanoparticles within Hexagonally Packed Cylindrical Domains of Diblock Copolymers in Bulk

We present a simple method to prepare hexagonally packed metallic nanocylinders based on gold nanoparticles embedded in a copolymeric matrix. The gold nanoparticles are generated selectively within the P4VP-rich cylindrical domains of a polystyrene-b-poly-4-vinylpyridine (PS-b-P4VP) diblock copolymer. In order to achieve this selectivity, a gold precursor (HAuCl4) is coupled to the pyridine blocks of a spherical PS327-b-P4VP27 block copolymer. In consequence, the hybrid block copolymer is able to self-assemble in a hexagonally packed cylinders morphology. The application of mechanical oscillatory shear improved markedly the alignment of these nanocylinders, while simultaneously the gold precursor was reduced in situ into gold nanoparticles. Following rheological characterization in the linear viscoelastic regime, a set of alignment parameters were comprehensively selected and checked with a series of transmission electron microscopy (TEM) micrographs. An optimal temperature of alignment was found after systematic evaluation of samples sheared at different temperatures. The block copolymer exhibited an increase in the domain period as a consequence of chain rearrangements around the newly formed gold nanoparticles. The hexagonally packed morphology was preserved, and under the optimal conditions single grain sizes showed significant improvement to macroscale order in comparison to nonaligned samples. In contrast to current multistep lithographic techniques, the present method constitutes a simple path to produce three-dimensional organic-inorganic conductive nanowires with periodicities at the macroscopic level.

Room-temperature discotic liquid-crystalline coronene diimides exhibiting high charge-carrier mobility in air

Six N,N′,5,11-tetrasubstituted coronene-2,3,8,9-tetracarboxydiimides have been synthesised incorporating 3,4,5-tri(n-dodecyloxy)phenyl or 2-(n-decyl)-n-tetradecyl groups in various positions. Differential scanning calorimetry, polarised optical microscopy, and X-ray diffraction indicate that all form columnar discotic mesophases from around room temperature to around 200 °C. Charge-carrier mobility values, which energetic considerations suggest are electron mobility values, have been determined in non-aligned samples cooled from the isotropic melt using the space-charge-limited current technique. The highest mobility, 6.7 cm2V−1 s−1, was found in N,N′-bis(n-2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecylfluorooctyl)-5,11-bis(3-[{3,4,5-tri(n-dodecyloxy)phenyl}carbonyloxy]-n-propyl)coronene-2,3,8,9-tetracarboxydiimide, which X-ray diffraction suggests is the most highly ordered of the materials examined.

Mössbauer morphological analysis of Fe-filled multiwalled carbon nanotube samples

We have performed morphological analysis of samples of Fe nanowires encapsulated into aligned multiwalled carbon nanotubes (Fe-MWCNTs) via Fe57 Mössbauer spectroscopy. The aligned Fe-MWCNTs were obtained by pyrolysis of ferrocene onto an oxidized Si substrate. Transmission Mössbauer spectroscopy (TMS) and backscattered conversion electron Mössbauer spectroscopy (CEMS) were applied in order to distinguish different Fe phases and their spatial distribution within the whole sample and along the tubes’ height. A characterization (on a large spatial scale) of the aligned CNT samples was performed by obtaining TMS spectra for selected spots positioned at different locations of the sample. While the total Fe content changes considerably from one location to another, the γ-Fe∕α-Fe phase ratio is constant onto a relatively large area. Using TMS and CEMS for all aligned Fe-MWCNT samples it is also shown that along the CNT axes, going to the top of the nanotube the relative content of the γ-Fe phase increases. Going to the opposite direction, i.e., towards the silicon substrate, the relative content of the Fe3C phase increases, which is in agreement with our previous works. The results of an additional Mössbauer spectroscopy experiment in TMS and CEMS modes performed on a nonaligned sample support the conclusion that in our case the iron phases in the channels of carbon nanotubes are spatially separated as individual nanoparticles. The relative intensity ratio of the α-Fe phase Mössbauer sextets shows good magnetic texture along the nanotubes’ axis for one of the aligned samples and the lack of such orientation for the others.