Shielding Anisotropy Research Articles

Multinuclear solid state NMR spectroscopy of ternary rare-earth silicides RET 2Si2 and germanides LaT 2Ge2 (RE = Sc, Y, La, Lu; T = Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, Au)

Abstract A series of ternary rare earth – transition metal – tetrelides RET 2 Tt 2 (RE = Sc, Y, La, Lu; T = Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, Au; Tt = Si, Ge) was synthesized by arc melting of the elements and subsequent annealing. The samples were characterized by powder X-ray diffraction and in addition, the structures of REOs2Si2 (RE = Y, La, Lu), LaAu2Si2, LaAg2Ge2 and LaAu2Ge2 were refined from single crystal X-ray diffractometer data. The tetrelides crystallize with the ThCr2Si2 type (I4/mmm) except the platinum compounds which adopt the klassengleiche superstructure of the CaBe2Ge2 type (P4/nmm). The transition metal atoms have tetrahedral tetrel coordination and the tetrahedra condense to layers via common edges. The stacking of these layers leads to Tt−Tt bonds in the ThCr2Si2 type phases and heteroatomic T−Tt bonds in the CaBe2Ge2 type phases. The rare earth atoms fill larger cages within these three-dimensional networks (coordination number 16 with RE@T 8 Tt 8) with site symmetries 4/mmm (ThCr2Si2 type) and 4mm (CaBe2Ge2 type). Systematic multinuclear solid state NMR spectroscopic investigations allowed observing the effect of the involved rare-earth metal, transition metal and tetrel group element, respectively. In particular, 29Si isotropic resonance shifts can be predicted from element-specific increments and interatomic Si–Si bonding interactions manifest themselves in axially symmetric magnetic shielding anisotropies.

Accurate Prediction of NMR Chemical Shifts: Integrating DFT Calculations with Three-Dimensional Graph Neural Networks.

Computer prediction of NMR chemical shifts plays an increasingly important role in molecular structure assignment and elucidation for organic molecule studies. Density functional theory (DFT) and gauge-including atomic orbital (GIAO) have established a framework to predict NMR chemical shifts but often at a significant computational expense with a limited prediction accuracy. Recent advancements in deep learning methods, especially graph neural networks (GNNs), have shown promise in improving the accuracy of predicting experimental chemical shifts, either by using 2D molecular topological features or 3D conformational representation. This study presents a new 3D GNN model to predict 1H and 13C chemical shifts, CSTShift, that combines atomic features with DFT-calculated shielding tensor descriptors, capturing both isotropic and anisotropic shielding effects. Utilizing the NMRShiftDB2 data set and conducting DFT optimization and GIAO calculations at the B3LYP/6-31G(d) level, we prepared the NMRShiftDB2-DFT data set of high-quality 3D structures and shielding tensors with corresponding experimentally measured 1H and 13C chemical shifts. The developed CSTShift models achieve the state-of-the-art prediction performance on both the NMRShiftDB2-DFT test data set and external CHESHIRE data set. Further case studies on identifying correct structures from two groups of constitutional isomers show its capability for structure assignment and elucidation. The source code and data are accessible at https://yzhang.hpc.nyu.edu/IMA.

Vertically aligned carbon fiber/polydimethylsiloxane composites prepared by lyophilization with exceptional thermal conductivity and electromagnetic interference shielding performance

Composites with high thermal conductivity and exceptional electromagnetic interference (EMI) shielding properties are crucial for ensuring the long-term stability of electronic devices. One-dimensional carbon fibers (CFs) stand out as promising materials due to their excellent thermal and electrical conductivity. However, the anisotropic nature of CFs limits the overall electrical and thermal conductivity of the composite, thus impeding its practical application. To address this limitation, we investigated the effect of different freezing methods on CF orientation using the ice template method. Subsequently, CF-150/PDMS and CF-250/PDMS composites with varying average lengths of CFs were prepared using the unidirectional freezing technique. We studied the influence of CF content and average length on the anisotropic thermal conductivity and EMI shielding properties of the composites. The CF-250/PDMS composite, with a CF content of 15.71 vol%, exhibits a remarkable thermal conductivity of 9.07 W·m−1·K−1 and a low thermal resistance of 2.61 °C·cm2‧W−1. The thermal conductive mechanism of CF/PDMS composites was simulated by thermal conduction model and finite element analysis. Furthermore, it demonstrates longitudinal electromagnetic interference shielding effectiveness (EMI SE) reaches up to 39.66 dB, while the transverse EMI SE reaches up to 52.55 dB. The vertically aligned CF/PDMS composites exhibit significant potential for a range of applications in thermal management and EMI shielding.

Anisotropic electromagnetic wave shielding performance in Janus cellulose nanofiber composite films

Herein, Janus multi-walled carbon nanotubes/cellulose nanofibers/poly (3, 4-ethylenedioxythiophene):polystyrene sulfonate (CNT/CNF/PEDOT:PSS) composite films were prepared via a layer-by-layer vacuum filtration to achieve anisotropic electromagnetic wave shielding materials. Conductive CNT/CNF and PEDOT:PSS are located on both sides of the composite film to create Janus structure, while insulated CNF acts as an intermediate layer to separate the two conductive layers. The Janus conductive structure of the composite film gives anisotropic electromagnetic interference shielding effectiveness (EMI SE). The EMI SE values of electromagnetic waves incident from the CNT/CNF layer and PEDOT:PSS layer are much different. The average differentiation of SE at two sides (ΔSE‾) values are much dependent on surface conductive differentiation and thickness of middle layer. The maximum ΔSE‾ can reach 20.5 dB for the samples with 60 % CNT in CNT/CNF layer, 2 ml PEDOT:PSS solution in PEDOT:PSS layer and 50 mg CNF in middle layer. In addition, the electromagnetic simulation is also carried to discuss the anisotropic shielding mechanism of the samples. The simulation results are consistent with the experimental results to further explore the EMI mechanism of the Janus composite films.

Foam with direction: unraveling the anisotropic radiation shielding properties of 2D boron nitride nanoplatelet foams

Neutron radiation exposure is one of the main challenges faced during space missions. There is a critical need for advanced lightweight radiation shielding materials. Two-dimensional (2D) boron nitride nanoplatelets (BNNP) are excellent candidates for polymer matrix nanofillers due to their superior neutron shielding and thermal and mechanical properties. Furthermore, the 2D material anisotropic behavior unlocks the potential for composite property tailoring. This study fabricated ultra-lightweight lamellar BNNP foams (density 0.05 g cm–3 and 97.5% porous) via freeze-drying processing. The neutron shielding effectiveness or mass absorption coefficient of the BNNP foams with walls perpendicular to the direction of the radiation source was 14.47 cm2 g–1, while that of the foam with parallel configuration was only 8.51 cm2 g–1. The orientation-dependent neutron radiation shielding properties were modeled using the Beer-Lambert law for porous composite materials. The BNNP foam in this study has the potential to benefit advanced tailorable radiation shielding technologies for future aerospace missions.

Hybrid Foams based on Multi‐Walled Carbon Nanotubes and Cellulose Nanocrystals for Anisotropic Electromagnetic Shielding and Heat Transport

AbstractLightweight and mechanically robust hybrid foams based on cellulose nanocrystals (CNC) and multi‐walled carbon nanotubes (MWCNT) with an anisotropic structure are prepared by directional ice‐templating. The anisotropic hybrid CNC‐MWCNT foams displayed a combination of highly anisotropic thermal conductivity and an orientation‐dependent electromagnetic interference (EMI) shielding with a maximum EMI shielding efficiency (EMI‐SE) of 41–48 dB between 8 and 12 GHz for the hybrid foam with 22 wt% MWCNT. The EMI‐SE is dominated by absorption (SEA) which is important for microwave absorber applications. Modelling of the low radial thermal conductivity highlighted the importance of phonon scattering at the heterogeneous CNC‐MWCNT interfaces while the axial thermal conductivity is dominated by the solid conduction along the aligned rod‐like particles. The lightweight CNC‐MWCNT foams combination of an anisotropic thermal conductivity and EMI shielding efficiency is unusual and can be useful for directional heat transport and EMI shielding.

The EFG Rosetta Stone: translating between DFT calculations and solid state NMR experiments.

We present a comprehensive study on the best practices for integrating first principles simulations in experimental quadrupolar solid-state nuclear magnetic resonance (SS-NMR), exploiting the synergies between theory and experiment for achieving the optimal interpretation of both. Most high performance materials (HPMs), such as battery electrodes, exhibit complex SS-NMR spectra due to dynamic effects or amorphous phases. NMR crystallography for such challenging materials requires reliable, accurate, efficient computational methods for calculating NMR observables from first principles for the transfer between theoretical material structure models and the interpretation of their experimental SS-NMR spectra. NMR-active nuclei within HPMs are routinely probed by their chemical shielding anisotropy (CSA). However, several nuclear isotopes of interest, e.g.7Li and 27Al, have a nuclear quadrupole and experience additional interactions with the surrounding electric field gradient (EFG). The quadrupolar interaction is a valuable source of information about atomistic structure, and in particular, local symmetry, complementing the CSA. As such, there is a range of different methods and codes to choose from for calculating EFGs, from all-electron to plane wave methods. We benchmark the accuracy of different simulation strategies for computing the EFG tensor of quadrupolar nuclei with plane wave density functional theory (DFT) and study the impact of the material structure as well as the details of the simulation strategy. Especially for small nuclei with few electrons, such as 7Li, we show that the choice of physical approximations and simulation parameters has a large effect on the transferability of the simulation results. To the best of our knowledge, we present the first comprehensive reference scale and literature survey for 7Li quadrupolar couplings. The results allow us to establish practical guidelines for developing the best simulation strategy for correlating DFT to experimental data extracting the maximum benefit and information from both, thereby advancing further research into HPMs.

Dual cross-linked and vertically oriented MXene/polyvinyl alcohol aerogel for ultrabroadband electromagnetic interference shielding and thermal camouflage

Lightweight and porous conductive aerogels have demonstrated great potential in electromagnetic interference (EMI) shielding and thermal camouflage, while the poor mechanical properties and structural stability usually limit their applications. Herein, vertically oriented and physically/chemically dual cross-linked Ti3C2TX MXene/polyvinyl alcohol (PVA) composite aerogel is prepared by ice-templated unidirectional freezing process and subsequent glutaraldehyde (GA) treatment. GA induced covalent crosslinking leads to the significantly enhanced structural stability and mechanical strength of the resultant MXene/PVA composite aerogels, which also endows them with desirable flame retardancy. The honeycomb-like structure of the composite aerogel contributes to its good anisotropic absorption-dominated EMI shielding performance over an ultrabroadband frequency range (8.2–40 GHz) with a low MXene content of 3.81 vol%. Furthermore, the excellent thermal insulation properties and low infrared emissivity of the highly oriented arranged MXene sheets bring the composite aerogel promising applications in thermal camouflage. Therefore, the lightweight and robust MXene/PVA composite aerogel demonstrates great potential in multi-scenario applications as a high-performance multifunctional EMI shielding material.

Electronic Structure, Aromaticity and Optical Properties of Dehydro[10]annulene.

Dehydro[10]annulene had been prepared experimentally recently, which is considered to be a highly rigid structure with planar configuration. In this paper, the electronic structure and bonding character of dehydro[10]annulene had been studied by means of molecular orbital (MO), density of states (DOS), bond order (BO) and interaction region indicator (IRI) analyses. The delocalization characters of out-of-plane and in-plane π-electrons (πout - and πin -electrons) of the bond regions were studied by using localized orbital locator (LOL). The anisotropy of the induced current density (AICD), iso-chemical shielding surface (ICSS) and anisotropy of the gauge-including magnetically induced current (GIMIC) were used to investigate the molecular response to external magnetic field, including the induced ring current and the magnetic shielding characteristic. The results showed that the electron delocalization of dehydro[10]annulene is mainly contributed by πout system. The apparent clockwise current in the πout system proved that dehydro[10]annulene is πout aromatic. Finally, the photophysical properties and (hyper)polarizability of dehydro[10]annulene were studied by TD-DFT calculation. The results showed that dehydro[10]annulene has strong local excitation characters. Its (hyper)polarizability decreases with the increase of frequency and has the characteristics of nonlinear anisotropy.

Anisotropic Shape Memory Composite for Dynamically Adjustable Electromagnetic Interference Shielding

Smart electromagnetic interference (EMI) shielding materials that enable dynamical adjustment of electromagnetic wave transmission are highly desirable for various applications. Nevertheless, ordinary materials show nonadjustable EMI shielding performance after deployment. Herein, an anisotropic smart EMI shielding composite is presented, which shows tunable EMI shielding effectiveness by rotation, shape memory, and simple stacking. The composite possesses a sandwich structure consisting of two graphene fibrous films (GFFs) with intermediate shape memory poly(ethylene-co-vinyl acetate) (EVA). Owing to the aligned graphene fibers of GFF, the GFF/EVA composite showed anisotropic mechanical property, shape memory property, and shielding effectiveness. The composite shows high tensile strength but declined shape memory property in the axial direction (0°) of the graphene fibers. In the 0° direction of the GFF/EVA composite, a total shielding effectiveness (SET) of >40.8 dB in the X-band is observed, which is much higher than that in the 90° direction (vertical, <8.1 dB). The rotation-modulated EMI shielding of GFF/EVA is achieved by the anisotropy-dependent EMI shielding performance. Moreover, tunable EMI shielding is demonstrated through the shape memory process of the composite and the average SET can be adjusted in the range from 43.2 to 33.1 dB by fixing a tensile strain from 0 to 100%. Furthermore, the EMI shielding of the multilayered composite can be modulated by stacking individual GFF/EVA composites at different angles. The smart GFF/EVA composite with tunable and function-switchable features is demonstrated, which will contribute to the development of smart EMI shielding materials and devices for electromagnetic applications in various fields.

Composite phase change materials embedded into cellulose/polyacrylamide/graphene nanosheets/silver nanowire hybrid aerogels simultaneously with effective thermal management and anisotropic electromagnetic interference shielding

Exploiting an advanced material simultaneously with effective thermal management (TM) and electromagnetic interference (EMI) shielding capacity is ungently demanded yet challenging for the miniaturized and integrated electronics. Anisotropic networks can be impregnated with phase change materials (PCMs) to fabricate multifunctional shape-stable PCMs (ss-CPCMs) simultaneously with excellent TM and EMI shielding, which is rarely reported. Herein, the anisotropic cellulose/polyacrylamide/graphene nanosheet/silver nanowire (CPGxAy) hybrid aerogels were successfully prepared using directional freeze-drying method, and then utilized as supporting skeletons to embed polyethylene glycol (PEG) via vacuum-assistant impregnation. Profited by the synergistic effect of graphene nanosheets (GNPs) and silver nanowires (AgNWs), the resultant polyethylene glycol@cellulose/polyacrylamide/graphene nanosheet/silver nanowire hybrid aerogel (PEG@CPGxAy) ss-CPCMs exhibit fascinating thermal conductivity (TC) of 0.84 W/m·K (200% increase in comparison with that of pure PEG) and anisotropic average EMI shielding effectiveness (SE) of 71.08 dB along the transverse direction and 35.21 dB along the longitudinal direction, while remaining high melting and crystallization enthalpy efficiency of 93.47% and 93.08%, respectively. In addition, PEG@CPGxAy ss-CPCMs also display great shape stability, thermal stability, and cyclic reusability in the storing/releasing latent heat processes. This investigation sheds new light on designing and fabricating ss-CPCMs with pretty comprehensive properties for TM and EMI shielding of modern electronics.Graphical Abstract

Methods for Determination of Absolute Configurations of Chiral Diols by THENA Ester and NMR Shift Difference

AbstractDetermination of the absolute configuration of chiral secondary diols by chiral derivatizing agent (CDA) and NMR shift difference is of great challenge due to the complication from the interference of the aromatic anisotropic shielding effect of the two CDAs in close proximity. In this work, tetrahydro-1,4-epoxynaphthalene-1-carboxylic acid (THENA) was introduced as an alternative CDA for diols to overcome such complexity. Since the deshielding effect of THENA is weaker than the shielding effect of other CDAs, THENA would allow the direct analysis of the chemical shift difference in determining the absolute configuration of the chiral diols. In addition, an analytical method based on Riguera’s model could also be used to confirm the assignment. With a good agreement between the assigned configuration based on both analytical models, the absolute configuration of the chiral diols could be assigned with reliability.

Chemical shielding and electric field gradient tensors of disodium 5′-adenosine triphosphate trihydrate determined by solid-state NMR spectroscopy and ab initio calculations

The tri-phosphate and sodium ion environments in well crystallized disodium 5′adenosine triphosphate trihydrate (ATP•3H2O) are investigated using high-resolution solid-state NMR spectroscopy and ab initio calculations. The six inequivalent phosphorus sites resolved in 31P MAS spectra have been assigned on the basis of experimentally obtained results and theoretical ab initio quantum chemical calculations of 31P chemical shielding tensors with increased numerical accuracy. Aided by 31P-31P dipolar connectivity established in DQ-SQ correlation experiment and DFT calculations carried out at the B3LYP/(aug-cc-pDVZ(3s,2p,1d), 6–31G(d,p)) level, phosphorus resonance assignments in MAS spectra have been made and the 31P chemical shielding anisotropies and tensor orientations in the molecule-fixed frame have been determined. 31P shielding tensors are found to be oriented with the most shielded direction nearly perpendicular to the O-P-O plane involving the two adjoining oxygens. The complete resolution of the four sodium sites has been achieved from 3Q-MAS experiments performed at 7.05 T and this has enabled 23Na quadrupole parameters to be determined experimentally and compared with theoretical calculations. Besides aiding a partial resonance assignment of the 23Na 3Q-MAS spectrum, our HF/6–311++G(2d,2p) calculations of 23Na EFG tensors show that for two sodium sites which are tightly coordinated the orientation of the EFG tensor is distinct. These exhibit unique directions along which the field gradient is the smallest and largest.

Graphene fibre film/polydimethylsiloxane nanocomposites for high-performance electromagnetic interference shielding.

Exploration of high-performance electromagnetic interference (EMI) shielding materials has become a trend to address the increasing electromagnetic (EM) wave pollution environment. In this paper, oriented graphene fibre film (GFF)/polydimethylsiloxane (PDMS) nanocomposites with one-ply unidirectional, two-ply cross-ply, and two-ply unidirectional configurations were prepared using wet-spinning and hot-pressing techniques in a two-step process. Due to the anisotropic electrical performance of GFF, the one-ply laminate exhibits EMI shielding anisotropy that is affected by fibre orientation relative to the electric field component in EM waves. The maximum shielding difference at 8.8 GHz is up to 32.0 dB between the fibre orientation parallel to and perpendicular to the electric field component. In addition, we found that adding a layer of GFF is an intuitive method to enhance the shielding efficiency (SE) of GFF/PDMS nanocomposites by providing more interfaces to enhance absorption losses. An optimal EMI shielding performance of a two-ply unidirectional laminate is observed with an SE value of 50.6 dB, which shields 99.999% of EM waves. The shielding mechanisms are also discussed and clarified from the results of both experimental and theoretical analyses by adjusting the GFF structural parameters, such as the fibre orientation, areal density, number of plies and stacking sequence.

Isolated Solid Wall-Assisted Thermal Conductive Performance of Three-Dimensional Anisotropic MXene/Graphene Polymeric Composites.

The introduction of three-dimensional (3D) continuous conformations in polymer materials is a convincing proposal for acquiring the desirable multifunction to fulfill the urgent demands of highly integrated electronic devices. However, the limited functional design of the filled aligned network remains challenging. Herein, directional self-assembly 3D MXene/graphene aerogels are fabricated as conductive networks for polyethylene glycol (PEG) matrix. Based on the uniaxial and biaxial ice template method, the temperature gradient affects the aligned arrangement of the 3D microstructure. The biaxial PEG/MXene/GR composites exhibit an enhanced through-plane thermal conductivity of 1.64 W m-1 K-1 at 10.6 vol % content, which is 522% higher than that of pure PEG. The influence of the biaxial self-assembly strategy compared with that of the uniaxial one on the thermal conductivity reaches the highest 333% when the weight ratio equals 1:1. Meanwhile, the same difference also occurs in the electromagnetic shielding interference (EMI) property. The advanced EMI-shielding effectiveness of the biaxial PM1G1 composites reaches ∼36 dB at the 2.5 mm thickness. This research provides valuable guidance for designing high-performance applications of anisotropic thermal management and EMI shielding in 5G telecommunications and mobile electronic devices.

SWCNTs Interaction with Dopamine and Serotonin Anticancer Through QM/MM Methods: A Drug Delivery Approaches

Objetive: Dopamine and Serotonin are the two important biological transmitters that have hormonal activities and responsible for happiness and felling well. The aim of this article was to study theoretically the structure features of Dopamine and Serotonin in the complex of single-walled carbon nanotube as a neurotransmitter. Material and Methods: The structure of Dopamine and Serotonin binding with SWCNT with four different diameters (7.0,7.5,7.7,10.0 nm) was studied by using molecular mechanic (MM) and quantum mechanic (QM). The remarkable energies including potential energy, total energy and kinetic energy in time of simulation 10 ns steps in two temperatures (298, 310 kelvin degree) were investigated by Monte Carlo method with opls force filed. NMR shielding tensor data by B3LYP level of theory with 6-31 G(d) as a basis set and semi empirical method have been also fulfilled. Results: Theoretical computations were performed to study NMR chemical shift data including magnetic shielding tensor (σ, ppm), shielding asymmetry (η), magnetic shielding anisotropy (σaniso), magnetic shielding isotropy (σiso) , skew of a tensor (Κ) and chemical shift anisotropy (Δσ) and span (Ω) at various rotation angles around a specific rotation, physical and chemical properties of atomic nuclei. Semi empirical calculations such as total energy, binding energy, isolated atomic energy, electronic energy, core–core interaction and heat of formation in AM1 were revealed. Conclusion: It is figured out in Monte Carlo method our two specific drug and its nanotube with small diameter are the most stable one than the others. The larger diameter leads the combination stability into lower value.

Effective Local Geometry Descriptor for 29Si NMR Q4 Anisotropy

The nuclear shielding anisotropy, ζ, is a useful nuclear magnetic resonance (NMR) shielding tensor parameter in describing the extent of electron cloud distortion about an atom. Despite the advantages afforded by NMR in structural characterization, the relationship between ζ and local structure of an atom in high-symmetry environments, such as Si–Q4 sites, is poorly understood. Here, we use a data-driven approach combining random forest feature ranking and the Sure Independence Screening and Sparsifying Operator (SISSO) approach to derive a simple and accurate geometric descriptor for ζ with a root-mean-squared prediction error of 6.77 ppm and an R2 of 0.761. We then apply this descriptor to describe the local geometric distortion of zeolites Sigma-2 and silica-ZSM-5 whose chemical shift anisotropy tensor has been reported. We envision that this geometric descriptor will allow for structural description and refinement in previously difficult-to-describe materials.

Ultrathin, Ultralight, and Anisotropic Ordered Reduced Graphene Oxide Fiber Electromagnetic Interference Shielding Membrane

AbstractDeveloping an electromagnetic interference (EMI) shielding material with lightweight, ultrathin, and high‐performance complex electromagnetic wave pollution has become a research trend. Here, a novel ultrathin ordered reduced graphene oxide fiber (oRGOF) membranes are reported with wrinkles, grooves, and hierarchical structure by a simple assembly process based on wet spinning. The results show that the oRGOF membranes have obvious anisotropic conductivity and directional electromagnetic shielding properties. The measured electrical conductivity along the fiber axial direction (0°) is higher than that along the fiber radial direction (90°). Furthermore, the EMI shielding performance difference under different rotation angles is more than 25 dB (31.0 dB at 0°, 4.9 dB at 90°). The thickness of the resultant oRGOF membrane is 0.03 mm and area density of 0.9 mg cm−2, and the specific EMI SE (SSE/t) is 33333 dB cm2 g−1 along the fiber axis. The oRGOF membranes show flexible and durable performance under repeated bending and straightening cycles tests over 160 times, without significant reduction of the shielding performance. Thus, the ultrathin, ultralight, and anisotropic oRGOF electromagnetic interference shielding membrane have broad prospects for both civilian and military applications.

Investigation of different SWCNTs interaction with dopamine and serotonin anticancers: a theoretical study

Carbon nano tubes (CNTS) have two basic structure as single-walled and multi-walled based on hexagonal plexus of carbon atoms. CNTs can serve as platforms to conjugate other compounds specially in medications purposes by immobilization of biomolecules at their surface. Dopamine and serotonin are two biological molecules which have bifunctional activities as hormone and neurotransmitter. These two molecules have important roles as neurotransmitters in the central and peripheral nervous systems but serotonin functions as a mood regulator, while dopamine is connected to the “pleasure center”. In this article we optimized molecular and structural properties of connected dopamine and serotonin with SWNTS with four different diameters (7.0,7.5,7.7 and 10.0 nm) by using molecular quantum methods such as NMR shielding tensor data by B3LYP level of theory with 6-31 G(d) as a basis set, mk and frequency methods. Theoretical computations were performed to study NMR chemical shift data including magnetic shielding tensor (σ, ppm), shielding asymmetry (η), magnetic shielding anisotropy (σaniso), magnetic shielding isotropy (σiso) , skew of a tensor (Κ) and chemical shift anisotropy (Δσ) and span (Ω) at various rotation angles around a specific rotation , physical and chemical properties of atomic nuclei , frequency data by B3LYP/6-31g level of theory and POP method using gaussian 09 program.

Enhanced electromagnetic shielding property and anisotropic shielding behavior of corrugated carbon fiber felt composite and its sandwich structure

This work fabricated flat, corrugated, and corrugated sandwich short-chopped carbon fiber (SCF) felt/epoxy resin matrix composites for understanding the effect of fiber orientation in three-dimensional space on electromagnetic shielding property. Electromagnetic interference shielding effectiveness (EMI SE) in X band was experimentally investigated and electromagnetic simulation was carried out for investigating the surface current distribution. The results show that EMI SE of corrugated SCF felt composite decreases from 39.8 dB to 18.7 dB (@8.2 GHz) when the angle between transverse corrugated direction and field polarization direction increases from 0° to 90°, indicating obvious in-plane anisotropic shielding property. Corrugated sandwich SCF felt composite consisting of two flat and one corrugated felts has excellent EMI SE (>70 dB) in X band, which mainly results from multiple reflection in corrugated core. This kind of composite possesses good anti-compression ability and great deformability, demonstrating great potential in application of structural–functional integration and light-weight shielding composites.