Ostwald ripening of oil-in-water emulsions stabilized by phenoxy-substituted dextrans

The stability of oil-in-water emulsions prepared using dextran, a natural polysaccharide, hydrophobically substituted with phenoxy groups, was studied. The evolution of the emulsion droplet size was investigated as a function of polymer concentration (Cp=0.2 to 1% w/w in a water phase) and the degree of phenoxy substitution (tau=4.2 to 15.7%). For the highest tau values, emulsions, which presented submicrometer droplets, were stable over more than 4 months at room temperature. The most substituted polymers clearly showed a better efficiency to lower the surface tension at the oil/water interface. DexP did not induce real viscosification of the continuous phase. The linearity of the particle volume variation with time, and the invariability of the volume distribution function, proved that Ostwald ripening was the main destabilization mechanism of the phenoxy dextran emulsions. The nature of the oil dispersed phase drastically affected the behavior of emulsions. While the emulsions prepared with n-dodecane presented a particle growth with time, only few size variations occurred when n-hexadecane was used. Furthermore, small ratios of n-hexadecane in n-dodecane phase reduced the particle growth due to the lower solubility and lower diffusion coefficient in water of n-hexadecane, which acted as a ripening inhibitor.     

Random replicators with high-order interactions

We use tools of the equilibrium statistical mechanics of disordered systems to study analytically the statistical properties of an ecosystem composed of N species interacting via random mutual interactions, as well as via deterministic self-interactions of order p>/=2. We show that the main effect of increasing the order of the interactions among the species is to make the system less competitive, in the sense that the fraction of extinct species is greatly reduced. In addition, we find that for p>2 there is a threshold value which gives a lower bound to the concentration of the surviving species, preventing then the existence of rare species and, consequently, increasing the robustness of the ecosystem to external perturbations.     

Phase behavior and rheological properties of enzymatically synthesized trehalose decanoate aqueous solutions

Surface tension properties of an enzymatically synthesized equimolar mixture of trehalose mono- and didecanoate in aqueous solutions have been determined. At 20 degrees C a critical micellar concentration (CMC) of 50 micromol/l and a minimal surface tension of 28 mN/m have been obtained. Above the CMC, it has been shown that up to a concentration of 42 wt%, and in a 20-60 degrees C temperature range the sugar ester aqueous solutions do not form any crystalline structure, nor present any phase transition, and the trehalose decanoate molecules form an isotropic worm-like micellar phase. The rheological properties indicate however a more complicated picture in the same concentration and temperature ranges. In steady shear, the viscosity of the trehalose decanoate solutions do not exhibit any shear rate dependence from 1 to 100 s(-1) for concentrations up to 42 wt%. Below 0.8 wt%, the viscosity remains constant and close to that of water; then, between 0.8 and 23 wt%, the viscosity shows a quadratic increase with surfactant concentration. For higher concentrations, up to 42 wt%, no further significant increase in viscosity is observed. In oscillatory shear experiments, the solutions exhibit viscoelastic properties. The observed rheological behavior as a function of concentration and temperature may be due to a progressive evolution of the trehalose decanoate molecular associations: as the concentration increases, the system evolves towards an entangled and/or partially branched or cross-linked micellar network, and eventually a multiconnected network of cross-linked micelles.     

PEO‐Covered Nanoparticles by Emulsion Inversion Point (EIP) Method

This study reports the first PEO‐coated polymer nanoparticles synthesis by miniemulsion polymerization of nano‐emulsions prepared by the low‐energy emulsification method called EIP. The surfactant used was Brij 98, a PEO based non ionic commercial surfactant. The partial phase diagram of the system water/Brij 98/styrene was first determined. The Emulsion Inversion Point technique was then used on the water/Brij 98/styrene system to the formation of styrene‐in‐water nano‐emulsions. After miniemulsion polymerization, particle sizes as low as 36 nm were obtained. To the best of our knowledge, this method had not been used for polymerizable system up to now.

     

Spherical ensembles of gold nanoparticles on silica: electrostatic and size effects

Core-shell ensembles of citrate-stabilized gold nanoparticles (20-80 nm) on submicron silica cores (330-550 nm) have been prepared by electrostatic self-assembly with shell packing densities as high as phi = 0.55.     

Maturation of auditory temporal integration and inhibition assessed with event-related potentials (ERPs)

Background

We examined development of auditory temporal integration and inhibition by assessing electrophysiological responses to tone pairs separated by interstimulus intervals (ISIs) of 25, 50, 100, 200, 400, and 800 ms in 28 children aged 7 to 9 years, and 15 adults.

Results

In adults a distinct neural response was elicited to tones presented at ISIs of 25 ms or longer, whereas in children this was only seen in response to tones presented at ISIs above 100 ms. In adults, late N1 amplitude was larger for the second tone of the tone pair when separated by ISIs as short as 100 ms, consistent with the perceptual integration of successive stimuli within the temporal window of integration. In contrast, children showed enhanced negativity only when tone pairs were separated by ISIs of 200 ms. In children, the amplitude of the P1 component was attenuated at ISIs below 200 ms, consistent with a refractory process.

Conclusions

These results indicate that adults integrate sequential auditory information into smaller temporal segments than children. These results suggest that there are marked maturational changes from childhood to adulthood in the perceptual processes underpinning the grouping of incoming auditory sensory information, and that electrophysiological measures provide a sensitive, non-invasive method allowing further examination of these changes.     

Nanoprobe implantation into mammalian cells by cationic transfection

Submicron-sized Au particles and Au/SiO(2) nanocomposites (superparticles) as large as 670 nm have been introduced into tsA201 cells with minimal cell trauma by cationic transfection systems. Successful implantations can be characterized by the expression of co-transfected DNA.