Spherulitic networks : from structure to rheological property

A finite element method based on ABAQUS is employed to examine the correlation between the microstructure and the elastic response of planar Cayley treelike fiber networks. It is found that the elastic modulus of the fiber network decreases drastically with the fiber length, following the power law. The power law of elastic modulus G′ vs the correlation length ξ obtained from this simulation has an exponent of −1.71, which is close to the exponent of −1.5 for a single-domain network of agar gels. On the other hand, the experimental results from multidomain networks give rise to a power law index of −0.49. The difference between −1.5 and −0.49 can be attributed to the multidomain structure, which weakens the structure of the overall system and therefore suppresses the increase in G′. In addition, when the aspect ratio of the fiber is smaller than 20, the radius of the fiber cross-section has a great impact on the network elasticity, while, when the aspect ratio is larger than 20, it has almost no effect on the elastic property of the network. The stress distribution in the network is uniform due to the symmetrical network structure. This study provides a general understanding of the correlation between microscopic structure and the macroscopic properties of soft functional materials.

Effect of a commercial alcohol ethoxylate surfactant (C11–15E7) on biodegradation of phenanthrene in a saline water medium by Neptunomonas naphthovorans

Biodegradation of poorly soluble polycyclic aromatic hydrocarbons (PAHs) has been a challenge in bioremediation. In recent years, surfactant-enhanced bioremediation of PAH contaminants has attracted great attention in research. In this study, biodegradation of phenanthrene as a model PAHs solubilized in saline micellar solutions of a biodegradable commercial alcohol ethoxylate nonionic surfactant was investigated. The critical micelle concentration (CMC) of the surfactant and its solubilization capacity for phenanthrene were examined in an artificial saline water medium, and a type of marine bacteria, Neptunomonas naphthovorans, was studied for the biodegradation of phenanthrene solubilized in the surfactant micellar solutions of the saline medium. It is found that the solubility of phenanthrene in the surfactant micellar solutions increased linearly with the surfactant concentrations, but, at a fixed phenanthrene concentration, the biodegradability of phenanthrene in the micellar solutions decreased with the increase of the surfactant concentrations. This was attributed to the reduced bioavailability of phenanthrene, due to its increased solubilization extent in the micellar phase and possibly lowered mass transfer rate from the micellar phase into the aqueous phase or into the bacterial cells. In addition, an inhibitory effect of the surfactant on the bacterial growth at high surfactant concentrations may also play a role. It is concluded that the surfactant largely enhanced the solubilization of phenanthrene in the saline water medium, but excess existence of the surfactant in the medium should be minimized or avoided for the biodegradation of phenanthrene by Neptunomonas naphthovorans.

Predator control promotes invasive dominated ecological states

Invasive species are regarded as one of the top five drivers of the global extinction crisis. In response, extreme measures have been applied in an attempt to control or eradicate invasives, with little success overall. We tested the idea that state shifts to invasive dominance are symptomatic of losses in ecosystem resilience, due to the suppression of apex predators. This concept was investigated in Australia where the high rate of mammalian extinctions is largely attributed to the destructive influence of invasive species. Intensive pest control is widely applied across the continent, simultaneously eliminating Australia’s apex predator, the dingo (Canis lupus dingo). We show that predator management accounts for shifts between two main ecosystem states. Lethal control fractures dingo social structure and leads to bottom-up driven increases in invasive mesopredators and herbivores. Where control is relaxed, dingoes re-establish top–down regulation of ecosystems, allowing for the recovery of biodiversity and productivity.

Chemical immobilization of adult female Weddell seals with tiletamine and zolazepam: effects of age, condition and stage of lactation

Background

Chemical immobilization of Weddell seals (Leptonychotes weddellii) has previously been, for the most part, problematic and this has been mainly attributed to the type of immobilizing agent used. In addition to individual sensitivity, physiological status may play an important role. We investigated the use of the intravenous administration of a 1:1 mixture of tiletamine and zolazepam (Telazol®) to immobilize adult females at different points during a physiologically demanding 5–6 week lactation period. We also compared performance between IV and IM injection of the same mixture.
Results

The tiletamine:zolazepam mixture administered intravenously was an effective method for immobilization with no fatalities or pronounced apnoeas in 106 procedures; however, there was a 25 % (one animal in four) mortality rate with intramuscular administration. Induction time was slightly longer for females at the end of lactation (54.9 ± 2.3 seconds) than at post-parturition (48.2 ± 2.9 seconds). In addition, the number of previous captures had a positive effect on induction time. There was no evidence for effects due to age, condition (total body lipid), stage of lactation or number of captures on recovery time.
Conclusion

We suggest that intravenous administration of tiletamine and zolazepam is an effective and safe immobilizing agent for female Weddell seals. Although individual traits could not explain variation in recovery time, we suggest careful monitoring of recovery times during longitudinal studies (> 2 captures). We show that physiological pressures do not substantially affect response to chemical immobilization with this mixture; however, consideration must be taken for differences that may exist for immobilization of adult males and juveniles. Nevertheless, we recommend a mass-specific dose of 0.50 – 0.65 mg/kg for future procedures with adult female Weddell seals and a starting dose of 0.50 mg/kg for other age classes and other phocid seals.

Ilmenite FeTiO3 nanoflowers and their pseudocapacitance

Pronounced and stable pseudocapacitance has been found in flowerlike FeTiO3 nanostructures that were synthesized from ball-milled ilmenite (natural mineral) under mild hydrothermal conditions. Each nanoflower is composed of many thin petals with a thickness of 5–20 nm and a width of 100–200 nm. The formation of these flowerlike nanostructures is attributed to a dissolution–precipitation mechanism involving an intermediate sodium-containing phase. Electrochemical properties of the obtained FeTiO3 nanostructures are evaluated in aqueous electrolytes. The capacitance of 122 ± 14.5 F/g is measured in 1 M KOH aqueous electrolyte at the current rate of 500 mA/g, and 50 ± 6 F/g is retained at 5 A/g. The material has good long-term cycling stability. According to our data, FeTiO3 nanostructures show functionality as an electrode material for supercapacitors.

Measurement of forces due to structure in hydrocarbon liquids

Direct measurements of the force between two molecularly smooth mica sheets immersed in cyclohexane show not a monotonic van der Waals attraction, but an oscillatory function of distance, where the spacing between successive minima corresponds to the molecular diameter of cyclohexane. As surface separation increases the oscillations become less pronounced, and beyond 5 nm (typically seven or eight oscillations) they are no longer detected. These results accord with theoretical ideas on structural forces resulting from the inhomogeneous arrangement of molecules of the liquid near the solid surface. In n-octane the force law does not show the same pronounced oscillations, except at very small separations where repulsive barriers are found. These are attributed to the difficulty of removing the last layers of adsorbed molecules of the liquid from the mica surfaces, and they reduce the mice-mica adhesion significantly. Small amounts of water in the hydrocarbon liquids condense to form a bridge between the surfaces at small separations, causing a very strong adhesion between them. Some implications of these results for the stability of colloids in organic media are discussed.

Double-layer and hydration forces measured between silica sheets subjected to various surface treatments

Force measurements between silica surfaces in aqueous solutions of NaCl are reported. Silica is prepared with one of three surface treatments: (i) flaming, (ii) exposure to steam for 150 h, and (iii) brief exposure to ammonia vapor. Analysis of electrical double-layer interactions indicates that the surface density of silanol groups increases with steam treatment, and that exposure to ammonia etches the surface slightly and renders it porous. The force at short range is dominated by a strong repulsion which is attributed to hydration of the surface. The hydration component of the force is not significantly affected by the surface treatments, nor by electrolyte concentration over the range investigated (up to 0.1 M).

Forces due to structure in a thin liquid crystal film

Measurements of the force as a function of distance between two solids separated by a liquid crystal film give information on the structure of the film. We report such measurements for two molecularly smooth surfaces of mica separated by the nematic liquid crystal 4'-n-pentyl 4-cyanobiphenyl (5CB) in both the planar and homeotropic orientations at room temperature. The force is determined by measuring the deflection of a spring supporting one of the mica pieces, while an optical technique is used to measure the film thickness to an accuracy of ± (0.1-0.2) nm. The technique also allows the refractive indices of the nematic to be measured, and hence a determination of the average density and order parameter of the liquid crystal film as a function of its thickness. Three distinct forces were measured, each reflecting a type of ordering of the liquid crystal near the mica surfaces. The first one results from elastic déformation in the liquid crystal ; it was only observed in a twisted planar sample where the 5CB molecules are oriented in different directions at the two mica surfaces. The second, measured in both the planar and homeotropic orientations, is attributed to an enhanced order parameter near the surfaces. Both of these are monotonic repulsive forces measurable below 80 nm. Finally, there is a short-range force which oscillates as a function of thickness, up to about six molecular layers, between attraction and repulsion. This results from ordering of the molecules in layers adjacent to the smooth solid surface. It is observed in both the planar and homeotropic orientations, and also in isotropic liquids.