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1.
Manipulation and organization of ferromagnetic nanowires by patterned nematic liquid crystals 总被引:1,自引:0,他引:1
Lapointe CP Reich DH Leheny RL 《Langmuir : the ACS journal of surfaces and colloids》2008,24(19):11175-11181
We introduce a method to manipulate and organize ferromagnetic nanowires using the elastic forces imposed on nanowires suspended in nematic liquid crystals via patterned variations in the nematic director. As a test case for the technique, we investigate nematic environments consisting of stripes of alternating director orientations formed by lithographically patterned substrates. Nanowires oriented by small external magnetic fields are driven by the liquid crystal to specific locations of the pattern. The observed forces on the nanowires agree with calculations based on nematic elasticity. 相似文献
2.
Co、Ni及其合金纳米线阵列的制备及磁性研究 总被引:1,自引:0,他引:1
采用交流电化学沉积法,在多孔阳极氧化铝(AAO)模板孔洞中成功组装了铁磁性金属Co、Ni、CoNi合金纳米线阵列并采用扫描电子显微镜(SEM)、X射线衍射(XRD)等对样品进行表征。结果表明,Co、Ni及CoNi合金阵列体系中纳米线均匀有序,形状各向异性较大(长径比达30以上),有显著的结晶择优取向。对Co、Ni、CoNi合金纳米线阵列体系进行磁性分析,振动样品磁强计(VSM)测试结果显示,纳米线有明显的磁各向异性,适合用作垂直磁记录介质。纳米线阵列退火后沿纳米线方向矫顽力和矩形比减小,样品的垂直磁各向异 相似文献
3.
在电场和磁场下手性侧链丙烯酸酯液晶聚合物的行为江雪平金顺子漆宗能张树范(中国科学院化学研究所北京100080)关键词手性侧链丙烯酸酯液晶聚合物,红外二向色性,液晶分子排列含有手性液晶基团的聚合物,分子中含有不对称碳原子,在一定条件下使液晶聚合物... 相似文献
4.
An approach is described for controlling the spatial organization of mammalian cells using ferromagnetic nanowires in conjunction with patterned micromagnet arrays. The nanowires are fabricated by electrodeposition in nanoporous templates, which allows for precise control of their size and magnetic properties. The high aspect ratio and large remanent magnetization of the nanowires enable suspensions of cells bound to Ni nanowires to be controlled with low magnetic fields. This was used to produce one- and two-dimensional field-tuned patterning of suspended 3T3 mouse fibroblasts. Self-assembled one-dimensional chains of cells were obtained through manipulation of the wires' dipolar interactions. Ordered patterns of individual cells in two dimensions were formed through trapping onto magnetic microarrays of ellipsoidal permalloy micromagnets. Cell chains were formed on the arrays by varying the spacing between the micromagnets or the strength of fluid flow over the arrays. The positioning of cells on the array was further controlled by varying the direction of an external magnetic field. These results demonstrate the possibility of using magnetic nanowires to organize cells. 相似文献
5.
Growth of single-crystalline Ni and Co nanowires via electrochemical deposition and their magnetic properties 总被引:2,自引:0,他引:2
Pan H Liu B Yi J Poh C Lim S Ding J Feng Y Huan CH Lin J 《The journal of physical chemistry. B》2005,109(8):3094-3098
Single-crystalline Ni nanowires have been successfully fabricated with anodic aluminum oxide as template by electrodeposition. Structural characterization (X-ray diffraction, XRD, and high-resolution transmission electron microscopy, HRTEM) shows that the single-crystalline Ni nanowire has a preferred orientation along the [220] direction. The effects of electrochemical deposition conditions on the structure of Ni nanowires are systematically studied to investigate the growth mechanism. Possible reasons for the growth of the single-crystalline Ni nanowires were discussed on the basis of electrochemistry and thermodynamics. These single-crystalline Ni nanowires have exhibited excellent magnetic properties (large anisotropy, large coercivity, and high remanence). By a similar process, single-crystalline Co nanowires with hexagonal close-packed (hcp) structure were achieved, also having large anisotropy, large coercivity (1.8 kOe), and high remanence ratio (80.8%). 相似文献
6.
The application of the technique of observing the light scattering from solid polymers for the study of amorphous phase separation, spherulitic crystallization, phase separation in crystalline polymers, and coarsening of liquid crystal polymers is reviewed. The effect of shear and electrical and magnetic fields on liquid crystal orientation is discussed and its application for constructing light control and display devices is considered. 相似文献
7.
Computational modeling of texture formation in coupled phase separation-phase ordering processes in polymer/liquid crystal mixtures is performed using a unified model based on the nematic tensor order parameter and gradient orientation elasticity. The computational methods are able to resolve defect nucleation, defect-defect interactions, and defect-particle interactions, as well as global and local morphological features in the concentration and order parameter spatiotemporal behavior. Biphasic structures corresponding to polymer dispersed liquid crystals (PDLCs), crystalline filled nematic (CFNs), and random filled nematics (RFNs) are captured and analyzed using liquid crystal defect physics and structure factors. Under spinodal decomposition due to concentration fluctuations, the PDLC structure emerges, and the nucleation and repulsive interaction of defects within nematic droplets leads to bipolar nematic droplets. Under spinodal decomposition due to ordering fluctuations, the CFNs structure emerges, and the stable polymer droplet crystal is pinned by a lattice of topological defects. For intermediate cases, where the mixture is unstable to both concentration and nematic order fluctuations, the RFN structure emerges, and polymer droplets and fibrils are pinned by a defect network, whose density increases with the curvature of the polymer-liquid crystal interface. The simulations provide an information of the role of topological defects on phase separation-phase ordering processes in polymer-liquid crystal mixtures. 相似文献
8.
A noncatalytic and template-free vapor transport process has been employed to prepare single-crystalline Sn nanowires with diameters of 10-20 nm. The growth of one-dimensional Sn nanowires follows the mechanism similar to the vapor-solid (V-S) mechanism. Two-dimensional square-shaped nanostructures were also found to form in the region of lower deposition temperatures. The rich morphology may be attributed to the competition in growth rate among different crystallographic planes. Structural characterization with high-resolution transmission electron microscopy showed that the nanowires and nanosquares grew in a preferential direction of [200]. The superconducting transition temperatures for Sn nanowires and Sn nanosquares were about 3.7 K, which was very close to that of bulk beta-Sn. Magnetization measurements showed that the critical magnetic fields for both Sn nanowires and Sn nanosquares increased significantly as compared to that of bulk Sn. 相似文献
9.
He L Hu Y Han X Lu Y Lu Z Yin Y 《Langmuir : the ACS journal of surfaces and colloids》2011,27(22):13444-13450
Interparticle magnetic dipole force has been found to drive the formation of dynamic superparamagnetic colloidal particle chains that can lead to the creation of photonic nanostructures with rapidly and reversibly tunable structural colors in the visible and near-infrared spectrum. Although most studies on magnetic assembly utilize simple permanent magnets or electromagnets, magnetic fields, in principle, can be more complex, allowing the localized modulation of assembly and subsequent creation of complex superstructures. To explore the potential applications of a magnetically tunable photonic system, we study the assembly of magnetic colloidal particles in the complex magnetic field produced by a nonideal linear Halbach array. We demonstrate that a horizontal magnetic field sandwiched between two vertical fields would allow one to change the orientation of the particle chains, producing a high contrast in color patterns. A phase transition of Fe(3)O(4)@SiO(2) particles from linear particle chains to three-dimensional crystals is found to be determined by the interplay of the magnetic dipole force and packing force, as well as the strong electrostatic force. While a color pattern with tunable structures and diffractions can be instantly created when the particles are assembled in the form of linear chains in the regions with vertical fields, the large field gradient in the horizontal orientation may destabilize the chain structures and produces a pattern of 3D crystals that compliments that of initial chain assemblies. Our study not only demonstrates the great potential of magnetically responsive photonic structures in the visual graphic applications such as signage and security documents but also points out the potential challenge in pattern stability when the particle assemblies are subjected to complex magnetic fields that often involve large field gradients. 相似文献
10.
采用双槽控电位法在阳极氧化铝(AAO)模板中制备了有序均一的[NiFe/Cu/Co/Cu]n多层纳米线阵列,并在不同温度下进行了热处理.利用X射线衍射(XRD)对热处理前后多层线的晶体结构进行了测试.考察了不同退火温度对多层线矫顽力、剩磁比、巨磁电阻(GMR)效应、磁灵敏度的影响.随热处理温度升高,多层纳米线中磁性微晶晶型取向越来越明显,晶体结构更均匀;多层纳米线的矫顽力和剩磁比先增大后减小.300°C下多层纳米线矫顽力达到最大值,GMR最大值可达59%,对应的磁电阻灵敏度(SV)为0.233%Oe-1. 相似文献
11.
This paper investigates the stability of simple static orientation patterns in a sample of smectic liquid crystal confined to a cylindrical annulus, when a magnetic field is applied. Four different arrangements are considered, covering cases where the layer normal is everywhere either radial or axial, and the (orthogonal) magnetic field is either radial, azimuthal or axial. A classification is given of the threshold radii for mechanical instabilities, and of the threshold magnetic fields for Freedericksz transitions for these cases, with strong anchoring at the boundaries. 相似文献
12.
R. R. Mukhin Yu. A. Serebrennikov B. F. Minaev Z. M. Muldakhmetov 《Theoretical and Experimental Chemistry》1988,24(1):88-92
An expression for the initial chemically induced dynamic electron polarization produced according to a triplet mechanism under the conditions of pumping by polarized light has been obtained under the assumption that the fluctuations of the orientation of a molecule in a liquid have the character of an uncorrelated Markov process. The expression obtained is valid for arbitrary values of the magnetic field strength and the viscosity of the solvent. Numerical calculations of the chemically induced dynamic electron polarization have been carried out for slow molecular rotations and in weak magnetic fields.Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 24, No. 1, pp. 96–100, January–February, 1988.We thank V. E. Gluzberg for his assistance in carrying out the numerical calculations. 相似文献
13.
In this paper, we demonstrate how to apply recently discovered ferromagnetic nematic liquid crystal for visualisation of magnetic fields. The material exhibits strong optical response to both external electric and magnetic fields, which gives us an opportunity to use it for the detection of an area of magnetic vector field in a way that both, the magnitude and the direction of a given field can be simultaneously measured. We discuss the physical model that describes the behaviour of ferromagnetic liquid crystal placed in a liquid crystal cell and demonstrate the method of extracting the information about an arbitrary magnetic field from the combination of magneto-optic and electro-optic response of the sample placed in that field. We have applied the principle to a special case, where magnetic field was visualised on a 2D area near a cylindrical permanent magnet. 相似文献
14.
Oh K Chung JH Riley JJ Liu Y Liu WK 《Langmuir : the ACS journal of surfaces and colloids》2007,23(23):11932-11940
The dielectrophoretic assembly of silicon carbide (SiC) nanowires in a microfluidic flow is shown to enhance the orientation and deposition yield of nanowires. The fluid flow delivers and orients the nanowires in the vicinity of a gap, and they are attracted and deposited by a dielectrophoretic force. Depending upon their lengths, the nanowires are selectively attracted to the gap because the dielectrophoretic force is largest when the lengths are comparable to the gap size. Precise control over the fluid flow and dielectrophoresis shows various interesting phenomena such as landing, shifting, and uniform spacing of nanowires during the assembly process. As a result, the precise control enables the selective positioning of nanowires only at the gap where the fluid direction is consistent with the electric field orientation. 相似文献
15.
16.
Regular-shaped metal nanocrystals and their ensembles can serve as ideal substrates for studying surface-enhanced Raman scattering (SERS). We synthesized well-defined silver nanowires for a systematic study of SERS signal with respect to polarization and structural ordering. The observed dependence on polarization direction confirms prior theoretical predictions that large electromagnetic (EM) fields are localized in the interstitials between adjacent nanowires. We show that these modes are largely dipolar in nature and rely on short-range EM coupling between nanowires. 相似文献
17.
Han DS Bae SY Seo HW Kang YJ Park J Lee G Ahn JP Kim S Chang J 《The journal of physical chemistry. B》2005,109(19):9311-9316
We characterized the structure and magnetic properties of Mn-incorporated GaP nanowires synthesized by thermal evaporation of GaP/Mn powders. The nanowires consist of twin-crystalline zinc blende GaP grown with the [111] direction and doped with about 1 at. % Mn. They are often sheathed with the bumpy amorphous outerlayers containing high concentrations of Mn and O. The ferromagnetic hysteresis curves at 5 and 300 K and temperature-dependent magnetization provide evidence for the ferromagnetism with the Curie temperature higher than room temperature. Magnetic properties of individual nanowires have been measured, showing a large negative magnetoresistance equal to about -5% at 5 K. We suggest that the Mn doping of GaP nanowires would form a dilute magnetic semiconductor. 相似文献
18.
Sierra-Sastre Y Choi S Picraux ST Batt CA 《Journal of the American Chemical Society》2008,130(32):10488-10489
Semiconductor nanowires are being actively investigated because of their unique physical properties and potential applications in nanoelectronics and optoelectronic devices. However, current hurdles for device integration include the lack of control over the orientation, location, and packing density of nanowires. This communication presents for the first time the use of a unique, bottom-up approach for the catalyzed growth of semiconductor nanowires via biological templating. High-density, vertically oriented growth of Ge nanowires with monodispersed diameters and spacings was achieved through patterning of very small sized (5-20 nm) Au nanoparticles using bacterial surface-layer proteins as a template. We envision the applicability of this biotemplating approach to a variety of nanowires and substrate materials. 相似文献
19.
We have recently reported that weak electromagnetic (EM) field exposure of chick embryos induces a response that can be used to protect against subsequent hypoxic insult. This work is continued here with an exposure response study using 20-min exposure to 60 Hz magnetic fields over a range of 2-10 microT. Once again, the biomarker used was induction of hypoxia protection. A sigmoidal response curve was found, with exposures to magnetic field strengths > or = 4 microT inducing maximum hypoxia protection (68% survival). We also attempted to determine whether the magnetic or induced electric component of the EM field was responsible for the observed protection. This was accomplished by making measurements with two different orientations of the magnetic fields (perpendicular and parallel to the major axis of the egg). Owing to the configuration of the embryo in the egg, the induced electric field at the embryo was lower when the magnetic field was parallel to the major axis even though the magnetic field strength was the same for each orientation. Exposure of the embryos to the parallel orientation resulted in a reduced protective response. An exposure-response curve generated for this orientation of the field also showed a more "drawn-out" appearance, consistent with the observed distribution of embryo positions within the egg. Our results suggest that the induced electric, not the applied magnetic field, plays a primary role in the protective effect observed in this chick embryo model. 相似文献
20.
Effects of external fields such as magnetic field and boundary conditions on supramolecular structure, molecular arrangement and the texture of the ethyl-cyanoethyl cellulose cholesteric liquid crystalline solutions were investigated. It was found that the molecules of (E-CE)C are oriented to perpendicular to the magnetic field and the diamagnetic anisotropy of (E-CE)C is negative. With homeotropic anchoring boundary condition, the molecules are aggregated with focal-conics arrangement the molecules are aggregated with planar arrangement with homogeneous anchoring boundary condition. The effects of the external field on the orientation of the cholesteric phase were influenced by the concentration of the solution because the twist power of the cholesteric was varied with the concentration. And the effects are also restrains by the surface tension of the interphase. 相似文献