No abstract

Generating polymer–metal structures by means of additive manufacturing offers huge potential for customized, sustainable and lightweight solutions. However, challenges exist, primarily with regard to reliability and reproducibility of the additively generated joints. In this study, the polymers ABS, PETG and PLA, which are common in material extrusion, were joined to grit-blasted aluminum substrates. Temperature dependence of polymer melt rheology, wetting and tensile single-lap-shear strength were examined in order to obtain appropriate thermal processing conditions. Joints with high adhesive strength in the fresh state were aged for up to 100 days in two different moderate environments. For the given conditions, PETG was most suitable for generating structural joints. Contrary to PETG, ABS–aluminum joints in the fresh state as well as PLA–aluminum joints in the aged state did not meet the demands of a structural joint. For the considered polymers and processing conditions, this study implies that the suitability of a polymer and a thermal processing condition to form a polymer–aluminum joint by material extrusion can be evaluated based on the polymer’s rheological properties. Moreover, wetting experiments improved estimation of the resulting tensile single-lap-shear strength.

Uniaxial ferromagnetic Ni nanorods were prepared by the anodic aluminum oxide (AAO) template method. Reversible magnetization changes, measured perpendicular to the texture axis, were analyzed in terms of the Stoner–Wohlfarth model (SW). Using empirical model parameters, a quantitative and consistent description of the orientation- and field-dependent magnetic torque per particle was achieved. The model was extended (eSW) to take into account the local rotation of the magnetic nanorods in a soft-elastic matrix. The nanorods were characterized regarding their size, using transmission electron microscopy (TEM), their magnetic moment and colloidal volume fraction, determined from static field-dependent optical transmission (SFOT) measurements, and their rotational shape factor, obtained from oscillating field-dependent optical transmission (OFOT). The eSW-model was used in the simulation of simple bending and torsion of thin composite filaments. These simulations were compared with experimental results with the focus on the effect of finite magnetic anisotropy and local elastic rotation on the field-induced deformation of soft nanocomposites. The high sensitivity of thin filaments enabled the investigation of torque-induced deformation at nanorod volume density as low as 10−4 at which particle-particle interactions were negligible. In addition, reprogramming of the magnetic texture by magnetization reversal and the resulting modification in the deformation pattern was investigated.

Nickel (Ni) nanorods were prepared by the anodized aluminum oxide (AAO) template method and dispersed in poly(acrylamide) (PAM) hydrogels. The deformation of the magnetoresponsive composites was studied with particular attention to the consequences of finite magnetic shape anisotropy as compared to rigid dipoles on the field-dependent torque. For comparison with experiments, the composite was described as an elastic continuum with a local magnetic torque density, applied by discrete particles and determined by the local orientation of their magnetic anisotropy axis with respect to the magnetic field. The mean magnetic moment of the single domain particles m and their volume density in the composite φvol were derived from the static field-dependent optical transmission (SFOT) of linear polarized light. The mechanical coupling between the particles and their viscoelastic environment was retrieved from the rotational dynamics of the nanorods using oscillating field-dependent optical transmission (OFOT) measurements. Field- and orientation-dependent magnetization measurements were analyzed using the Stoner–Wohlfarth (SW) model and a valid parameter range was identified by introducing an effective anisotropy constant KA as a new empirical model parameter. This adapted SW-model for quantitative description of the field- and orientation dependence of the magnetic torque was validated by measuring the local rotation of nanorods in a soft elastic hydrogel. Finally, torsional and bending deformation of thin magnetically textured composite filaments were computed and compared with experiments.

Chemical imaging technology combines molecular spectroscopy and digital imaging for rapid, non-invasive, non-contact and reagentless detection of biological warfare agents (BWA). Chemical imaging forms the basis for a new class of optical BWA detection technology, which is made inherently orthogonal by integrating multiple detection strategies into the same system. Modes of specimen interrogation include laser excited Raman scattering and fluorescence emission combined with digital imaging [1]. Each of these detection strategies operating independently provides a limited degree of sensitivity and specificity. By combining each of these detection modalities it is being shown that sensitivity and specificity increase.Chemical imaging technology resolves objects less than a micron in size and can do so in the presence of interfering materials such as encapsulating glass or plastic, food, water or other fluids, including bodily fluids, and environmental contaminants. Species classification and identification is performed by electronically querying a database of spatial and spectral signatures that describe the unique morphologies and molecular properties of threat species. Chemical imaging technology can simultaneously test for the presence of numerous threat agents, and adding database entries to detect new threat agents is a straightforward process that does not require significant sample preparation or handling.Chemical imaging enables spatial-specific spectra to be collected that are then used to unravel composite chemical signatures present in complex mixtures. This technique employs the use of multivariate statistical analysis routines, generally known as chemometrics, to further aid in the interpretation of complex mixtures even when multiple components are co-localized. Such tools can greatly reduce the incidence of false positives and false negatives and can provide a method to determine within seconds to minutes if a biothreat is present.For BWA detection, fluorescence spectroscopy is particularly useful for rapid screening of suspect biotic material. Raman spectroscopy is useful because each specimen exhibits a characteristic 'fingerprint' spectrum, resulting from various selection rules. Peak intensity, shape and position are used to determine molecular composition, conformation (crystalline phase, degree of order, strain, grain size, etc.) and concentration. The high degree of specificity of Raman spectroscopy is well known. Whereas traditional detection methods are not generally capable of detecting and identifying bacterial species at the single spore level, chemical imaging can be used to "fingerprint" bacterial spore types down to the single-spore level. Figure 1 shows fluorescence chemical imaging results for a mixture of bacterial endospores, namely Bacillus globigi (BG) and Bacillus stearothremophilus (BS). Fluorescence spectra (Fig. 1A), optical images (Fig. 1B), and fluorescence chemical images (Fig. 1C) are collected on a chemical imaging microscope (FALCON, ChemImage Corporation) having fluor...