Surfactant assisted dispersion of functionalized multi-walled carbon nanotubes in aqueous media

The dispersibility of unfunctionalized and three differently functionalized multi-walled carbon nanotubes (MWNTs) in the presence of anionic, cationic, and non-ionic surfactants was investigated. Significant differences in their dispersibility were revealed by UV–vis spectroscopy of the dispersed MWNTs. X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, streaming potential measurements as well as pH measurements were conducted to characterize the MWNTs and their dispersions. Based on this information, possible interaction mechanisms between the surfactants and the differently functionalized MWNTs are proposed in order to account for the distinct dispersibility observed. Aqueous sizings containing low weight fractions of MWNTs were used for on-line modification of glass fibre (GF) sizings and preparation of GF/polypropylene composites, resulting in enhanced mechanical properties.     

Acoustic emission study of environmental effects in thermally sprayed coatings

Acoustic emission is observed from flame- and plasma-sprayed NiAl, Al₂O₃TiO₂ and Al₂O₃ coatings exposed to water immediately after spraying. The greatest activity is observed for a Ni-20wt.%Al coating and the least activity is from 99.5 wt.% commercially pure Al₂O₃. The effect is ascribed to the propagation of coating defects (i.e. pores and/or microcracks) under the action of tensile residual stresses by a form of environmentally enhanced cracking.     

Compound-specific stable isotope analysis of soil mesofauna using thermally assisted hydrolysis and methylation for ecological investigations

Stable isotope mass spectrometric approaches are proving to be valuable tools in unravelling biotic interactions in complex ecosystems, yielding information on trophic preferences and functional roles of individual species. Gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) provides considerable opportunities to assist in studies concerned with ecosystem processes mediated by soil invertebrates and microorganisms by determination of delta(13)C values of individual compounds, for example, lipids, amino acids etc. However, techniques conventionally adopted for "wet" chemical extractions and derivatizations necessary for compound-specific stable isotope determinations restrict the size of soil organism that can be studied and can limit investigations of individuals or even parts of individuals. We demonstrate here that individual soil mesofauna can be probed directly for their fatty acid stable isotope signatures by pyrolysis-GC/C/IRMS. A thermally assisted hydrolysis and methylation (THM) reaction is described for the determination of delta(13)C fatty acid values using trimethylsulfonium hydroxide (TMSH). Authentic fatty acids, acyl lipids, and individual Collembola (Folsomia candida) raised on C(3) and C(4) isotopically labeled yeast were analyzed initially by py-GC/MS with TMSH and then by py-GC/C/IRMS. A kinetic isotope effect (KIE) observed with the THM reaction prevents direct calculation of the fatty acid delta(13)C values by simple mass balance equations. However, the KIE is shown to be both reproducible and robust and can therefore be accounted for by the use of correction factors. The fatty acid methyl ester compositions of individual F. candida and their respective delta(13)C values were determined and shown to agree with those obtained by conventional "wet" chemical procedures applied to much larger numbers of Collembola, thus enhancing the scope to which stable isotopes can be applied to the study of invertebrates in complex food webs in any environment.     

Synthesis and characterization of coprecipitation-derived ferrimagnetic glass-ceramic

Ferrimagnetic glass-ceramics could be used for magnetic induction hyperthermia. This technique is utilised for the destruction of solid neoplastic diseases by application of an alternating magnetic field. Biocompatible ferrimagnetic materials could be easily incorporated into a tumour and could generate heat mainly by hysteresis loss. A ferrimagnetic glass-ceramic in the system SiO₂–Na₂O–CaO–P₂O₅–FeO–Fe₂O₃ has been prepared by melting of the coprecipitation-derived raw materials. This glass-ceramic contains a unique crystalline phase, magnetite, embedded in an amorphous matrix. Magnetite crystals precipitate during cooling from melting temperature. This glass-ceramic would no longer require any nucleation and growth thermal treatment, since the maximal quantity of magnetite crystals was produced during cooling. The average unit-cell parameter, crystallite size of magnetite, and the quantitative ratio of the crystallographic phases in the glass-ceramic samples were evaluated using two different methods. Similar results were obtained with both methods. The magnetite crystals are about 50 nm in dimensions. The samples contain 45 wt% of magnetite, homogeneously distributed in the amorphous residual matrix. The as prepared glass-ceramic has a saturation magnetisation of 34 A·m²/kg and a coercive force of 6.7 kA/m. The estimated magnetic loss/cycle under the magnetic field up to 796 kA/m is around 1.45 mJ/g. The specific power loss of this glass-ceramic under a magnetic field of 40 kA/m and a frequency of 440 kHz is 25 W/g. This material showed a bioactive behaviour, as after 2 weeks of soaking in a simulated body fluid the formation of a hydroxylapatite layer on their surface was observed. This feature makes it also suitable for bone cancer.     

Time-resolved transmission through homogeneous scattering media: time-response effects

An analytical expression has been obtained that describes the time variation of time-resolved signals transmitted through or reflected by a homogeneous scattering slab as measured with a detection system having a square-impulse response. This expression can be used to improve the match between theoretical and experimental time-resolved signals measured with a system having a finite response time. It can also be used to assess the effect of a finite detection response time on the time-domain characterization of a turbid medium. The expression can be adapted to detection systems that are not time invariant.     

Barrier effects in dispersive media

The effect of barrier layers with a generalized dielectric response on the measurement of the dielectric properties of materials are investigated, using the cluster model of relaxation to represent both the bulk and barrier properties. It is shown that the Maxwell-Wagner response is a limiting case and only applicable when the series elements are perfect, non-dispersive capacitors and resistors. A number of experimentally investigated systems are examined and it is shown that there is clear evidence for the proposed model in a wide range of applications.     

Environmental effects on thermally induced multistability in unsymmetric composite laminates

The principles involved in the generation of thermal induced multistability in carbon fibre epoxy laminates have received much interest in the published literature. This work examines the effects of moisture absorption on the mechanical properties of these plates focussing on geometry and ‘snap-through’ loadings. Samples were monitored from a dry state until moisture equilibrium was achieved. It was observed that substantial changes in geometry and snap-through performance occurred as moisture content increased. As part of this work, a first order strain energy analysis was modified to incorporate a hygrothermal strain term to enable prediction of the laminate shape due to moisture content.     

Atmospheric effects on the thermally induced sintering of nanoparticulate gold films

Gold (Au) films were formed by sintering of Au nanoparticles (NPs) under gas flows of air, oxygen (O₂), nitrogen (N₂), or N₂ bubbled through formic acid (FA/N₂). The microstructure changes of the Au nanoparticulate films were studied when different atmospheres were applied. The Au film sintered under FA/N₂ showed the progressive agglomeration and grain growth with porosity in the film, while the film sintered under N₂ had NPs without participating grain growth. A necking between NPs was observed in the film, however, unnecked NPs were still found. The Au film sintered under O₂ atmosphere showed the NPs agglomeration with various sizes up to 50 nm. X-ray characteristic peaks of the (111)-preferred orientation were observed in all samples. All samples showed N–H stretching at 3200–3300 cm⁻¹ regardless of sintering atmosphere. Hydrocarbon chains (C–H) at 2850–3000 cm⁻¹ were detected in the film sintered under N₂. For the Au film sintered under O₂, C–H stretching at 2850–3000 cm⁻¹, C–H deformation at 1350–1470 cm⁻¹, and C–O stretching at 1200–1300 cm⁻¹ were observed. C–O stretching at 1600–1700 cm⁻¹ was observed for the film sintered under FA/N₂ atmosphere. The electrical resistance of the film was related with microstructures and organic residual materials left in the film. Even though either porosity or carbon residues were observed in the film, the sintering of NPs in FA/N₂ or N₂ showed the sheet resistance comparable to that of electroplated one.     

Temperature-dependence of the cation distribution in ferrimagnetic spinels

The cation distribution at some equilibrium temperature in ferrimagnetic spinels can be inferred provided the contributions to the cationic site energies are established. In some compounds, e.g. magnesioferrite, the distribution is strongly dependent on temperature. This is explained by taking into account suitable thermal energy terms in addition to electrostatic or crystal-field octahedral stabilisations. The Fe₃O₄/MgFe_3–O_4–(–1)/2 system is considered and the temperature-dependence in magnesioferrite is discussed. A comparison is made of the theoretical derivation with several experimental data.     

Muzzling social media: The adverse effects of moderating stakeholder conversations online

Many organizations struggle to meaningfully engage with their stakeholders on political, societal and environmental topics via social media. Often such discourses unravel into splintered and negative conversations, raising the question whether organizations can and should exercise some level of control and ‘steering’ in these conversations and, if so, how stakeholders would react to such ‘top down’ moderation. Existing studies lack empirical insights into the impacts of different levels of moderation in social media conversations on stakeholder attitudes. Two experimental studies were developed to test the effect of different levels of organizational moderation on stakeholder attitudes towards organizations. We show that increased levels of moderation negatively affect attitudes towards an organization, satisfaction with an organization's performance, and trust in the organization. Increased moderation also significantly undermines beliefs in the commitment of the organization to its stakeholders and control mutuality. This paper extends recent qualitative attempts to build new theory around stakeholder dialogues on social media by testing the effects of varying levels of moderation in such dialogues.     

Confocal fluorescence polarization microscopy in turbid media: effects of scattering-induced depolarization

We present an experimental and theoretical study of confocal fluorescence polarization microscopy in turbid media. We have performed an experimental study using a fluorophore-embedded polymer rod immersed in aqueous suspensions of 0.1 and 0.5 microm diameter polystyrene microspheres. A Monte Carlo approach to simulate confocal fluorescence polarization imaging in scattering media is also presented. It incorporates a detailed model of polarized fluorescence generation that includes sampling of elliptical polarization, excited-state molecular rotational Brownian motion, and dipole fluorescence emission. Using both approaches, we determine the effects of the number of scattering events, target depth, photon scattering statistics, objective numerical aperture, and pinhole size on confocal anisotropy imaging. From this detailed analysis and comparison of experiment with simulation, we determine that fluorescence polarization is maintained to depths at which meaningful intensity images can be acquired.     

Stokes polarimetry in multiply scattering chiral media: effects of experimental geometry

The spatial distribution of optical rotation alpha and surviving linear polarization fraction beta(L) of light scattered from cylindrical turbid chiral (glucose-containing) and achiral samples is studied using a linear Stokes polarimeter. alpha and beta(L) are measured in and off the incident plane as the detection angle changes from the forward to the backward direction. The experimental results exhibit a complex dependence on the detection geometry: alpha is more sensitive to glucose presence off the incident plane, whereas beta(L) exhibits larger effects in-plane, as validated by polarization sensitive Monte Carlo simulations. A rigorous methodology is presented for optimizing the experimental geometry in the polarimetric examinations of complex random systems.     

Liquid phase epitaxy of ferrimagnetic garnet double-layers for magneto-optics

Double-layers of (Yb, Pr, Bi)₃ (Fe, Ga) ₅O₁₂ garnet on [111] GGG have been obtained by liquid phase epitaxy from a single melt. Such stratified structures in which individual layers have the same optical properties but otherwise different magnetization axis are of interest in non-reciprocal integrated optical devices.     

Intrinsic fluorescence spectroscopy in turbid media: disentangling effects of scattering and absorption

The fluorescence from a turbid medium such as biologic tissue contains information about scattering and absorption, as well as the intrinsic fluorescence, i.e., the fluorescence from an optically thin sample of pure fluorophores. The interplay of scattering and absorption can result in severe distortion of the intrinsic spectral features. These distortions can be removed by use of a photon-migration-based picture and information from simultaneously acquired fluorescence and reflectance spectra. We present experimental evidence demonstrating the validity of such an approach for extracting the intrinsic fluorescence for a wide range of scatterer and absorber concentrations in tissue models, ex vivo and in vivo tissues. We show that variations in line shape and intensity in intrinsic tissue fluorescence are significantly reduced compared with the corresponding measured fluorescence.     

From nanoparticles to nanocrystalline bulk: percolation effects in field assisted sintering of silicon nanoparticles

Nanocrystalline bulk materials are desirable for many applications as they combine mechanical strength and specific electronic transport properties. Our bottom-up approach starts with tailored nanoparticles. Compaction and thermal treatment are crucial, but usually the final stage sintering is accompanied by rapid grain growth which spoils nanocrystallinity. For electrically conducting nanoparticles, field activated sintering techniques overcome this problem. Small grain sizes have been maintained in spite of consolidation. Nevertheless, the underlying principles, which are of high practical importance, have not been fully elucidated yet. In this combined experimental and theoretical work, we show how the developing microstructure during sintering correlates with the percolation paths of the current through the powder using highly doped silicon nanoparticles as a model system. It is possible to achieve a nanocrystalline bulk material and a homogeneous microstructure. For this, not only the generation of current paths due to compaction, but also the disintegration due to Joule heating is required. The observed density fluctuations on the micrometer scale are attributed to the heat profile of the simulated powder networks.