Water-repellent textile via decorating fibers with amphiphilic Janus particles

We investigated morphology and wetting properties of textiles modified by chemically immobilized amphiphilic micrometer and submicrometer large Janus particles. The Janus particles bind by their reactive side to the textile surface, while their hydrophobic side faces the environment. It was found that the character of immobilization of the Janus particles on textile depends on their size: larger particles bind between fibers, while smaller ones bind to the fiber surface. In both cases, immobilization of Janus particles results in the hydrophobization of the hydrophilic textile surface. Finally, we demonstrated that submicrometer large Janus particles are very efficient for the design of water-repellent textiles.     

纳米钯/铁双金属颗粒对一氯乙酸的脱氯

为了提高零价铁对氯代有机物还原脱氯的性能,采用还原沉淀法制备了纳米钯/铁双金属颗粒.利用X射线衍射(XRD)、X射线荧光光谱(XRF)、扫描电子显微镜(SEM)、透射电镜(TEM)、以及BET-N2比表面积法对纳米钯/铁双金属颗粒进行了表征.结果表明,制备的纳米钯/铁双金属颗粒中Fe主要以α-Fe0形式存在.纳米钯/铁双金属颗粒的直径约为30～50nm,比表面积约51m2/g.纳米钯/铁双金属颗粒对一氯乙酸还原脱氯的脱氯率是还原铁粉和纳米铁粉对一氯乙酸还原脱氯的脱氯率的7.9倍和1.7倍.     

Peculiarities in light scattering by spherical particles with radial anisotropy

Light scattering by a spherical particle with radial anisotropy is discussed by extending Mie theory to diffraction by an anisotropic sphere, including both the electric and the magnetic anisotropy ratio. It is shown that radial anisotropy may lead to great modifications in scattering efficiencies and field enhancement, elucidating the importance of anisotropies in the control of scattering. The capacity for nondissipating damping is demonstrated for anisotropic spheres with different signs in radial and transversal permittivities.     

Fabrication and characterization of asymmetric Janus and ternary particles

Asymmetric Janus and ternary silica particles with an average diameter of 450 nm were fabricated by sequentially arranged particle-embedding and surface-modification processes. Thermally induced embedding of particles into polymer-fiber substrates allowed for precise control of the degree of particle submergence and the subsequent chemical modification of the hemispherical exposed particle surfaces. In addition to Janus particles with the desired surface-functionality ratios of 1:2, 1:1, and 2:1, this unique fabrication approach was also used to produce complicated and well-defined heterogeneous materials, including bifunctionalized Janus and ternary particles. The bifunctionalized Janus particles were produced with two hemispherical surfaces alternately labeled with gold and iron oxide nanoparticles, which simultaneously enabled anisotropic surface-plasmon resonance and a magnetic response. Ternary particles were also constructed, yielding submicrometer spheres with functionalized equatorial belts. The surface distributions of functional components in these spherical materials were carefully examined for uniformities in particle embedding. Statistical analyses revealed that the functional components were distributed with a uniformity of over 80% for all of the asymmetric Janus and ternary particles.     

Stabilization of chromium ore processing residue (COPR) with nanoscale iron particles

Laboratory batch experiments were conducted on heavily contaminated groundwater and chromium ore processing residue (COPR) samples to determine the rate and extent of hexavalent chromium [Cr(VI)] reduction and immobilization by nanoscale iron particles. Laboratory synthesized nanoscale iron particles (<100 nm, specific surface area 35 m(2)/g) were used for this work. Groundwater ([Cr(VI)]=42.83 +/- 0.52 mg/L, pH 11.0+/-0.5) and COPR samples ([Cr(VI)] = 3280 +/- 90 mg/kg) were collected from an industrial site in New Jersey. Cr(VI) in the water and COPR samples was quickly reduced and precipitated out of the aqueous solution. The surface area normalized reaction rate constant of Cr(VI) reduction by nanoscale iron particles was 0.157 +/- 0.018 mg m(-2) min(-1), about 25 times greater than that by iron powders (100 mesh). One gram of nanoparticles can reduce 84.4-109.3mg Cr(VI) in the groundwater and 69.3-72.7 mg Cr(VI) in the COPR. This reduction capacity is 50-70 times greater than that of iron powders under the same experimental conditions.     

Dispersion of clusters of nanoscale silica particles using batch rotor-stators

Nanoparticle powders added into a liquid medium form structures which are much larger than the primary particle size (aggregates and agglomerates)-typically of the order of 10’s of microns. An important process step is therefore the deagglomeration of these clusters to achieve as fine a dispersion as possible. This paper reports the findings of a study on the dispersion of hydrophilic fumed silica nanoparticle clusters, Aerosil 200 V, in water using two batch rotor-stators: MICCRA D-9 and VMI. The MICCRA D-9 head consists of a set of teeth for the stator and another for the rotor, whereas the VMI has a stator with slots and a rotor which consists of a 4-bladed impeller attached to an outer set of teeth. The dispersion process, studied at different power input values and over a range of concentrations (1, 5, 10 wt.%), was monitored through the evolution of PSD. Erosion was found to be the dominant breakage mechanism irrespective of operating conditions or rotor-stator type. The smallest attainable size was also found to be independent of the power input or the design of the rotor-stator. Break up kinetics increased upon the increase of power input, and this also depended on the rotor-stator design. With MICCRA D-9 which has smaller openings on both the stator and rotor, the break up rate was faster. Increasing the particle concentration decreased break up kinetics. It could also be shown that operating at high concentrations can still be beneficial as the break up rate is higher when assessed on the basis of specific power input per mass of solids.     

纳米生物活性玻璃颗粒的制备及形态控制

采用溶胶-凝胶技术制备纳米生物活性玻璃颗粒, 通过在溶胶中加入柠檬酸来控制生物活性玻璃的形态结构。利用比表面积分析仪、 透射电子显微镜和扫描电子显微镜对纳米生物活性玻璃的结构和形成机制进行了表征。研究结果表明:采用柠檬酸作为水解催化剂可以方便地控制生物活性玻璃的纳米结构形态, 有利于制备较小粒径、 大比表面积和孔体积的生物活性玻璃。这种制备技术提供了一种简单、 低成本制备纳米生物活性玻璃并控制其纳米粒子形态的方法。      

Phase-field modeling of eutectic structures on the nanoscale: the effect of anisotropy

A simple phase-field model is used to address anisotropic eutectic freezing on the nanoscale in two (2D) and three dimensions (3D). Comparing parameter-free simulations with experiments, it is demonstrated that the employed model can be made quantitative for Ag–Cu. Next, we explore the effect of material properties and the conditions of freezing on the eutectic pattern. We find that the anisotropies of kinetic coefficient and the interfacial free energies (solid–liquid and solid–solid), the crystal misorientation relative to pulling, the lateral temperature gradient play essential roles in determining the eutectic pattern. Finally, we explore eutectic morphologies, which form when one of the solid phases are faceted, and investigate cases, in which the kinetic anisotropy for the two solid phases is drastically different.     

An investigation of anisotropy of cobalt-surface-modified ironoxide magnetic particles

Surface treatment experiments on nonstoichiometric iron oxide are described, along with a theoretical analysis which suggests that the uniaxial anisotropy of cobalt-surface-modified iron oxide particles is not induced by the magnetic field of the inner core of iron oxides, but rather is due to the shape anisotropy being larger than the magnetocrystalline anisotropy of imperfectly crystallized CoFe₂ O₄. It is concluded that the crystalline imperfection of CoFe₂O₄ on the outer layer of iron oxides particles decreases the magnetocrystalline anisotropy and limits the enhancement rate of the coercivity of cobalt-surface-treated iron oxide particles     

Phase transformation in nanoscale indium-tin alloy particles embedded in metallic matrices

The interfaces influence the phase stability of small particles. For embedded indium-tin alloy particles, the interface among the phases present within the particles and the matrix contribute significantly to the free energy and hence influences the phase stability at small sizes. Our results show that upon rapid cooling, we obtain a combination of larger two-phase alloy particles consisting of beta- and y-phases and very fine precipitates of In or Sn. Both beta- and gamma-phases possess an orientation relationship with Al. The in situ results suggest that the beta-rich phase gradually dissolved in the eutectic liquid before melting and the particles retain the facets much above the melting temperature of the alloy particle. We have tried to explain the formation and stability of these phases in terms of favorable nucleation kinetics.     

Inlaying nanoscale surface recess patterns with nanoscale objects

A simple and versatile approach to constructing patterns on a solid surface using nanoscale objects is demonstrated. The approach is essentially an inlaying process, in which recess patterns fabricated on a surface are selectively filled with nanoscale objects. The objects are anchored firmly on the surface due to the spatial confinement provided by the recess structures. Protein molecules and inorganic nanoparticles are used in this demonstration. Cyclic voltammetry is used to detect electron transfer signals from patterns of protein molecules. The approach suggests a potentially fast, high-throughput and versatile technique for constructing architectural structures on a solid surface using nanoscale objects.     

Synthesis of Janus composite particles by the template of dumbbell-like silica/polystyrene

Janus particles possess promising performances. It is challenging to develop new methods to control composition and microstructure of the particles. In this report, we describe a general template synthesis of several non-spherical Janus composite particles by the template of dumbbell-like silica/polystyrene (PS) Janus particles. Both PS and silica can be modified to introduce desired functional groups respectively, or induce crystallization of other materials on the particle surface. Especially, by favorable growth of materials within the sulfonated PS gel forming the core–shell structure at the polymer part, several new Janus hollow particles are obtained after removal of the PS core.     

Effect of exchange anisotropy on the hysteresis behavior of Co particles

Fine particles of fcc Co have been prepared in the size range of 50–350 Å by using the vapor deposition technique. The dependence of coercivity on particle size and temperature has been studied. The effect of surface passivation on the coercivity and its temperature dependence has also been investigated. A maximum coercivity of 1650 Oe and a saturation magnetization of 125 emu/g was obtained for a particle size of 275 Å. A very strong exchange anisotropy (shift ∼ 10.7 kOe) at cryogenic temperatures was found due to the core-shell morphology of the particles. The effect of particle size and temperature has been studied on the exchange anisotropy and on the hysteresis behavior of the particles.     

Paraelectric thin films by nanoscale engineering of epitaxy and planar anisotropy for microwave phase shifter applications

Epitaxial and (110) oriented paraelectric thin films of Ba0.60Sro.40TiO3 were grown on (100) oriented NdGaO3 orthorhombic substrates, and the nonlinear dielectric properties were studied at 10 GHz along selected in-plane crystallographic directions in the film thickness range of 25-1200 nm. The measured dielectric properties show strong residual strain and in-plane directional dependence. For instance, the in-plane relative permittivity is found to vary from as much as 500 to 150 along [110] and [001], respectively, in the 600 nm film. Tunability was found to vary from as much as 54% to 20% in all films and directions. In a given film, the best tunability is observed along the compressed axis in a mixed strain state, 54% along [110] in the 600 nm film. It is shown that, by nanoscale manipulation of epitaxy and planar anisotropy, the return loss and phase shift in a paraelectric can be tuned over a rather wide range. The approach presented herein opens avenues for obtaining various degrees of phase shift on the same film, enabling one with an additional degree of freedom in device design and fabrication as well as multifunctionality.