Self-assembly, foaming, and emulsifying properties of sodium alkyl carboxylate/guanidine hydrochloride aqueous mixtures

Unsaturated fatty acids may be extracted from various agricultural resources and are widely used as soaps in the industry. However, there also exist a large variety of saturated and hydroxy fatty acids in nature, but their metal salts crystallize at room temperature in water, hampering their use in biological and chemical studies or for industrial applications. Addition of guanidine hydrochloride (GuHCl) to sodium salt of myristic acid has been shown to prevent its crystallization in water, forming stable flat bilayers at room temperature. Herein, we extend this finding to two other saturated fatty acids (palmitic and stearic acids) and two hydroxyl fatty acids (juniperic and 12 hydroxy stearic acids) and study more deeply (by using small angle neutron scattering) the supramolecular assemblies formed in both saturated and hydroxyl fatty acid systems. In addition, we take the advantage that crystallization no longer occurs at room temperature in the presence of GuHCl to study the foaming and emulsifying properties of those fatty acid dispersions. Briefly, our results show that all fatty acids, even juniperic acid, which is a bola lipid, are arranged in a bilayer structure that may be interdigitated. Depending on the nature of the fatty acid, the systems exhibit good foamability and foam stability (except for juniperic acid), and emulsion stability was good. Those findings should be of interest for using saturated long chain (and hydroxyl) fatty acids as surfactants for detergency or even materials chemistry.     

Dynamic magnetic resonance microscopy of flour dough fermentation

Magnetic resonance microscopy was carried out at 9.4 T with a voxel volume of 117 x 117 x 500 microm(3) and temporal resolution was adjusted to 8.5 min for a dynamic follow-up of bread dough fermentation during 2 h at a constant temperature of 30 degrees C. An image analysis procedure based on gray levels mathematical morphology routines was performed to assess bubble distribution and cell wall thickness inside the imaged bread dough. The evolution of the extracted curves allows one to characterize quantitatively the amount of bubbles and their growth. Using this procedure, different bread doughs were examined to determine the impact of dough composition on the structure modification during fermentation.     

Novel lipid system forming hollow microtubes at high yields and concentration

There is considerable interest in constructing supramolecular hollow tube architectures based on amphiphilic molecules. This can be achieved by using relatively expensive synthetic lipids. Herein, we report on the facile preparation of self-assembled microtubes from a novel low-cost lipid mixture that does not require a previous chemical synthesis step and consists of the ethanolamine salt of 12-hydroxy-stearic acid in water. Tubes of more than 10 microm in length spontaneously form upon cooling from an isotropic solution. They exhibit inner and outer diameters of 400 and 600 nm, respectively, and their walls consist of concentric stacked bilayers of fatty acid salts, each separated by a layer of water.     

Self-assembly of fatty acid-alkylboladiamine salts

Long-chain fatty acids are insoluble in aqueous solution and form crystal precipitates. It is then of particular importance to determine the physicochemical parameters allowing their dispersion in water to improve their bioavailability and their utilization as surfactants. Herein, we report a study on salt-free catanionic systems in aqueous solution made of mixtures between palmitic or stearic fatty acids and alkylboladiamines (Abd's) differing by their alkyl chain length. Phase contrast microscopy, solid-state NMR, Fourier transform infrared spectroscopy, and small-angle neutron scattering were used to characterize the phase behavior of these systems at molar ratio of fatty acid to Abd of 1 and 2. Whatever the Abd and the molar ratio, fatty acids were embedded at low temperature in a bilayer gel phase which crystallizes after a period of rest. At an equimolar ratio, the gel phases transited upon raising the temperature to an isotropic phase made of worm-like micelles except in the case of the ethylenediamine chain for which a lamellar fluid phase was observed. At a molar ratio of 2 and high temperature, fatty acids were embedded in a lamellar fluid phase which self-orients with its stacking axis perpendicular to the magnetic field. However, for a long alkylboladiamine such as spermine, worm-like micelles formed. The phase behavior at high temperature is discussed in terms of molecular volume.     

Preparation of Swellable Hydrogel‐Containing Colloidosomes from Aqueous Two‐Phase Pickering Emulsion Droplets

The fabrication of stable colloidosomes derived from water‐in‐water Pickering‐like emulsions are described that were produced by addition of fluorescent amine‐modified polystyrene latex beads to an aqueous two‐phase system consisting of dextran‐enriched droplets dispersed in a PEG‐enriched continuous phase. Addition of polyacrylic acid followed by carbodiimide‐induced crosslinking with dextran produces hydrogelled droplets capable of reversible swelling and selective molecular uptake and exclusion. Colloidosomes produced specifically in all‐water systems could offer new opportunities in microencapsulation and the bottom‐up construction of synthetic protocells.     

Smart Foams: Switching Reversibly between Ultrastable and Unstable Foams

Smart foams: Ultrastable foams with an optimal foamability are obtained using hydroxy fatty acids tubes. The stabilization results from the adsorption of monomers at the air-water interface and from the presence of tubes in the plateau borders. Upon heating, tubes transform to micelles, leading to foam destabilization and thus to the first foams to exhibit temperature-tuneable stability.     

Study of structural and electronic transport properties of Ce-doped LaMnO3

The structural and electronic transport properties of La_1−x Ce _x MnO₃ (x=0.0–1.0) have been studied. All the samples exhibit orthorhombic crystal symmetry and the unit cell volume decreases with Ce doping. They also make a metal-insulator transition (MIT) and transition temperature increases with increase in Ce concentration up to 50% doping. The system La_0.5Ce_0.5MnO₃ also exhibits MIT instead of charge-ordered state as observed in the hole doped systems of the same composition.