The interlayer swelling and molecular packing in organoclays

Understanding the interlayer swelling and molecular packing in organoclays is important to the formation and design of polymer nanocomposites. This paper presents recent experimental and molecular simulation studies on a variety of organoclays that show a linear relationship between the increase of d-spacing and the mass ratio between organic and clay. A denser molecular packing is observed in organoclays containing surfactants with hydroxyl-ethyl units. Moreover, our simulation results show that the head (nitrogen) groups are essentially tethered to the clay surface while the long hydrocarbon chains tend to adopt a layering structure with disordered conformation, which contrasts with the previous assumptions of either the chains lying parallel to the clay surface or being tilted at rather precise angles. (c) 2005 Elsevier Inc. All rights reserved.

Effects of artificial foods on the blood chemistry of the Australian magpie

Bird feeding on residential property is a popular activity throughout Western countries. Advocates insist the practice is beneficial, while opponents maintain that it can result in a wide range of negative outcomes including malnutrition. The biological effects of 'backyard feeding' were studied in Australian magpies Gymnorhina tibicen during the non-breeding season in 1999 in the Greater Brisbane and the Lockyer Valley regions, south-east Queensland, Australia. Six magpie populations were selected and 70 birds were individually tagged for identification. The birds were provided with processed foods, 20-40 g per bird daily. To monitor the effects of the food, blood chemistry and body mass (BM) were used as indices. Significant effects were observed in BM and plasma cholesterol (PC), showing strong sensitivity to food provisioning. Significant effects on PC and uric acid were found only when birds were fed dog sausage. Results suggest that blood PC levels in magpies are readily influenced by, probably, the lipids present in food, and that the type of food can affect blood PC levels. These effects may occur widely among fed magpies if the influence that we demonstrated at plasma level can be generalized. Following the free-ranging study, six magpies were captured and subjected to a 6-day captive experiment to determine whether the selected foods had the potential to alter the birds' blood chemistry. It was found that all of the foods, when provided ad libitum, influence at least two of the three blood parameters (PC and non-esterified fatty acids). Due to its popularity, wildlife feeding will continue. To make wildlife-feeding activities truly sustainable, there is a need for further studies. This study clearly demonstrated that the physiology of wild magpies can be affected by 'backyard feeding'.

Optimum conditions for adsorptive storage

The storage of gases in porous adsorbents, such as activated carbon and carbon nanotubes, is examined here thermodynamically from a systems viewpoint, considering the entire adsorption-desorption cycle. The results provide concrete objective criteria to guide the search for the Holy Grail adsorbent, for which the adsorptive delivery is maximized. It is shown that, for ambient temperature storage of hydrogen and delivery between 30 and 1.5 bar pressure, for the optimum adsorbent the adsorption enthalpy change is 15.1 kJ/mol. For carbons, for which the average enthalpy change is typically 5.8 kJ/mol, an optimum operating temperature of about 115 K is predicted. For methane, an optimum enthalpy change of 18.8 kJ/mol is found, with the optimum temperature for carbons being 254 K. It is also demonstrated that for maximum delivery of the gas the optimum adsorbent must be homogeneous, and that introduction of heterogeneity, such as by ball milling, irradiation, and other means, can only provide small increases in physisorption-related delivery for hydrogen. For methane, heterogeneity is always detrimental, at any value of average adsorption enthalpy change. These results are confirmed with the help of experimental data from the literature, as well as extensive Monte Carlo simulations conducted here using slit pore models of activated carbons as well as atomistic models of carbon nanotubes. The simulations also demonstrate that carbon nanotubes offer little or no advantage over activated carbons in terms of enhanced delivery, when used as storage media for either hydrogen or methane.

Passive air sampling for persistent organic pollutants: Introductory remarks to the special issue

There have been a number of developments in the need, design and use of passive air samplers (PAS) for persistent organic pollutants (POPs). This article is the first in a Special Issue of the journal to review these developments and some of the data arising from them. We explain the need and benefit of developing PAS for POPs, the different approaches that can be used, and highlight future developments and needs. (c) 2006 Elsevier Ltd. All rights reserved.

Generic Technique to Generate Large Branched DNA Complexes

The inherent self-recognition properties of DNA have led to its use as a scaffold for various nanotechnology self-assembly applications, with macromolecular complexes, metallic and semiconducting nanoparticles, proteins, inter alia, being assembled onto a designed DNA scaffold. Such structures may typically comprise a number of DNA molecules organized into macromolecules. Many studies have used synthetic methods to produce the constituent DNA molecules, but this typically constrains the molecules to be no longer than around 100 base pairs (30 nm). However, applications that require larger self-assembling DNA complexes, several tens of nanometers or more, need to be generated by other techniques. Here, we present a generic technique to generate large linear, branched, and/or circular DNA macromolecular complexes. The effectiveness of this technique is demonstrated here by the use of Lambda Bacteriophage DNA as a template to generate single- and double-branched DNA structures approximately 120 nm in size.

Structural characteristics of GaSB / GaAs nanowire heterostructures grown by metal-organic chemical vapor deposition

Highly lattice mismatched (7.8%) GaAs/GaSb nanowire heterostructures were grown by metal-organic chemical vapor deposition and their detailed structural characteristics were determined by electron microscopy. The facts that (i) no defects have been found in GaSb and its interfaces with GaAs and (ii) the lattice mismatch between GaSb/GaAs was fully relaxed suggest that the growth of GaSb nanowires is purely governed by the thermodynamics. The authors believe that the low growth rate of GaSb nanowires leads to the equilibrium growth. (c) 2006 American Institute of Physics.

Influence of nanowire density on the shape and optical properties of ternary InGaAs nanowires

We have synthesized ternary InGaAs nanowires on (111)B GaAs surfaces by metal-organic chemical vapor deposition. Au colloidal nanoparticles were employed to catalyze nanowire growth. We observed the strong influence of nanowire density on nanowire height, tapering, and base shape specific to the nanowires with high In composition. This dependency was attributed to the large difference of diffusion length on (111)B surfaces between In and Ga reaction species, with In being the more mobile species. Energy dispersive X-ray spectroscopy analysis together with high-resolution electron microscopy study of individual InGaAs nanowires shows large In/Ga compositional variation along the nanowire supporting the present diffusion model. Photoluminescence spectra exhibit a red shift with decreasing nanowire density due to the higher degree of In incorporation in more sparsely distributed InGaAs nanowires.