Properties and sensing characteristics of surface-plasmon resonance in infrared light

Conditions of surface-plasmon resonance (SPR) production with use of IR pumping light (800-2300 nm) in the Kretschmann-Raether prism arrangement were investigated. Both calculations and experimental data showed that SPR characteristics in the IR are strongly influenced by the properties of the coupling prism material. Indeed, quite different regularities of plasmon excitation, polarity of sensing response, and sensitivity are observed for two different glasses and silicon. The observed differences in SPR properties are related to essentially different behavior of dispersion characteristics of materials near the SPR coupling point. Methods for improving sensor performance and miniaturizing the SPR technique using novel coupling materials (silicon) are discussed.     

Aerosol Generation of Nonspherical Particles by Desublimation of Copper Phthalocyanine

A novel generator for a defined test aerosol consisting of nonspherical particles was developed based on the desublimation of copper phthalocyanine during adiabatic cooling. Employing a brush disperser, copper phthalocyanine powder is dosed and dispersed in a nitrogen flow and sublimated in a tube furnace. Downstream the furnace new particles are formed due to the adiabatic expansion and the desublimation of the material in a laval nozzle. The generated particles were characterized employing a scanning mobility particle sizer and an aerosol particle mass analyzer to determine the size distribution and the dynamic shape factor. For the operating parameters of the generator examined here, particles with a mobility diameter between 30 and 600 nm were generated. The measured values for the dynamic shape factor of the particles were confirmed by scanning electron microscopy analysis.     

Mechanism of nanoparticle actuation by responsive polymer brushes: from reconfigurable composite surfaces to plasmonic effects

The mechanism of nanoparticle actuation by stimuli-responsive polymer brushes triggered by changes in the solution pH was discovered and investigated in detail in this study. The finding explains the high spectral sensitivity of the composite ultrathin film composed of a poly(2-vinylpyridine) (P2VP) brush that tunes the spacing between two kinds of nanoparticles-gold nanoislands immobilized on a transparent support and gold colloidal particles adsorbed on the brush. The optical response of the film relies on the phenomenon of localized surface plasmon resonances in the noble metal nanoparticles, giving rise to an extinction band in visible spectra, and a plasmon coupling between the particles and the islands that has a strong effect on the band position and intensity. Since the coupling is controlled by the interparticle spacing, the pH-triggered swelling-shrinking transition in the P2VP brush leads to pronounced changes in the transmission spectra of the hybrid film. It was not established in the previous publications how the actuation of gold nanoparticles within a 10-15 nm interparticle distance could result in the 50-60 nm shift in the absorbance maximum in contrast to the model experiments and theoretical estimations of several nanometer shifts. In this work, the extinction band was deconvoluted into four spectrally separated and overlapping contributions that were attributed to different modes of interactions between the particles and the islands. These modes came into existence due to variations in the thickness of the grafted polymeric layer on the profiled surface of the islands. In situ atomic force microscopy measurements allowed us to explore the behavior of the Au particles as the P2VP brush switched between the swollen and collapsed states. In particular, we identified an interesting, previously unanticipated regime when a particle position in a polymer brush was switched between two distinct states: the particle exposed to the surface of the collapsed layer and the particle engulfed by the swollen brush. On average, the characteristic distance between the particles and the islands increased upon the brush swelling. The observed behavior was a result of the anchoring of the particles to polymeric chains that limited the particles' vertical motion range. The experimental findings will be used to design highly sensitive optical nanosensors based on a polymer-brush-modulated interparticle plasmon coupling.     

Colloidal Occlusion Template Method for Micromanufacturing of Omniphobic Surfaces

An efficient strategy to produce forests of aligned nanowires and nail‐like micrometer‐sized structures, whose density can be tuned in a broad range, is reported in this study. It relies on a combination of two template‐assisted nanofabrication/patterning methods: electrochemical growth of metal nanowires in nanoporous sacrificial templates and partial masking of a surface with a self‐assembled colloidal monolayer. A great potential of this novel approach, termed here colloidal occlusion template method, is demonstrated on the example of the fabrication of omniphobic surfaces comprised of nickel micronails whose density is varied to approach highest possible contact angles. After chemical modification to reduce their surface tension, these microstructures with reentrant geometry support the non‐wetting Cassie state for both high‐surface‐tension water and low‐surface‐tension hexadecane. In particular, superhydrophobic behavior (contact angles exceeding 150°) is found for water, while oleophobicity (contact angles approaching 110°) is observed for hexadecane. The proposed approach can be exploited for the fabrication of a large variety of supported high‐aspect‐ratio nano/microstructures in applications where a surface density of features has to be several orders of magnitude lower than can be obtained with conventional template methods.     

Stress-Corrosion Cracking of AISI 4340 Steel in Aqueous Environments

Stress corrosion cracking of the high-strength martensitic steel AISI 4340 (yield stress = 1503 MPa) in NaCl aqueous solutions of different concentrations was studied experimentally using compact tension specimens in free corroding conditions. The experiments were conducted under the controls of constant load, constant crack opening displacement (COD), constant loading rate, and constant COD rate. Despite the differences in controlling conditions, the experiments yielded similar results for the threshold stress intensity factor and the plateau velocity in the 3.5 wt pct NaCl solution. Dependence of the plateau velocity on the NaCl concentration was observed, whereas the values of the threshold stress intensity factors seem to be independent of the NaCl concentration in distilled water.     

Wire-to-wire bonding of μm-diameter aluminum wires for the Electric Solar Wind Sail

We present a novel ultrasonic wire-to-wire bonding method for bonding two micrometer-thick metal wires together. A special jig and an industrial wire bonder perform the bonding. This wire-to-wire bonding is the core unit process to produce space tether for the Electric Solar Wind Sail. The proposed method was validated experimentally with 38 bonds where a 25 μm and a 50 μm by diameter Al wires that were first bonded together after which the bond was pull tested. The measured average pull force was (74 ± 15) mN whereas the lowest pull force value was 40 mN. The results show that wire-to-wire bonds of sufficient strength can be produced for the Electric Solar Wind Sail tether application. Tether manufacturing was demonstrated with a separate test where a 1.4 m long tether was produced featuring more than 100 wire-to-wire bonds.     

A semi‐analytic collocation technique for steady‐state strongly nonlinear advection‐diffusion‐reaction equations with variable coefficients

The aim of this paper is to present a new semi‐analytic numerical method for strongly nonlinear steady‐state advection‐diffusion‐reaction equation (ADRE) in arbitrary 2‐D domains. The key idea of the method is the use of the basis functions which satisfy the homogeneous boundary conditions of the problem. Each basis function used in the algorithm is a sum of an analytic basis function and a special correcting function which is chosen to satisfy the homogeneous boundary conditions of the problem. The polynomials, trigonometric functions, conical radial basis functions, and the multiquadric radial basis functions are used in approximation of the ADRE. This allows us to seek an approximate solution in the analytic form which satisfies the boundary conditions of the initial problem with any choice of free parameters. As a result, we separate the approximation of the boundary conditions and the approximation of the ADRE inside the solution domain. The numerical examples confirm the high accuracy and efficiency of the proposed method in solving strongly nonlinear equations in an arbitrary domain.     

The normal and oblique impact of three types of wet granules

Impact tests against a hardened steel plate have been carried out to obtain the coefficient of restitution of three types of spherical granules. The dominant elastic γ-Al₂O₃, the elastic-plastic zeolite 4A and the dominant plastic sodium benzoate have been chosen as granule samples. An electromagnetic canon has been constructed to accelerate the granules and to measure the normal coefficient of restitution. The moisture content of the granules has been varied so that the pore saturation ranges between of S = 0–1. Thereby, the influence of the moisture content on the normal coefficient of restitution could be determined. A free fall apparatus, on which the impact angle is changeable in the range of Θ_A = 0–80°, has been used to investigate the tangential coefficient of restitution. A high speed digital camera has been used to record the events of impact and rebound. The record frequency of the camera has been varied between 4,000 and 8,000 frames per second.