Agricultural spraying involves atomizing a liquid stream through a hydraulic nozzle, thus forming a liquid sheet that is subsequently destabilized into drops. Standard adjuvants such as dilute oil-in- water emulsions are known to influence the spray drop size distribution. Although being documented, the physical mechanisms at the origin of the size increase remain unclear. To elucidate the mechanisms causing the changes on the drop size distribution, we investigate the influence of dilute emulsions on the destabilization mechanisms of liquid sheets. Model laboratory experiments based on the collision of a liquid tear on a small solid target are used to produce and characterize liquid sheets. With dilute oil-in-water emulsions, the liquid sheet is destabilized during its expansion by the nucleation of holes that perforate the sheet and grow. The emulsion concentration and the size of the oil droplet of the emulsion are varied to rationalize their influence on the sheet destabilization mechanisms. The results obtained with the model laboratory experiments are compared to the measurement of the drop size distribution resulting from a conventional agricultural spray. The very good correlation between the number of perforation events and the volume fraction of small drops in the spray suggests (i) that the model experiment on liquid sheet is appropriate to investigate and gain an understanding of the physical mechanisms governing the spray drop size distribution and (ii) that the perforation destabilization mechanism of liquid sheets, which dominates for dilute emulsions, is at the origin of the increase of the size of the spray drops.

Surface activity and micelle formation of alkylguanidinium chlorides, containing 10, 12, 14, and 16 carbon atoms in the hydrophobic tail have been studied by combining conductivity and surface tension measurements with isothermal titration calorimetry. The purity of the resulting surfactants, their temperatures of Cr → LC and LC → I transitions, as well as their propensity of forming birefringent phases were assessed based on the results of 1H and 13C NMR, differential scanning calorimetry (DSC), and polarizing microscopy studies. Whenever possible, the resulting values of Krafft temperature (TK), critical micelle concentration (CMC), minimum surface tension above the CMC, chloride counter-ion binding to the micelle, and the standard enthalpy of micelle formation per mole of surfactant (micH°), were compared to those characterizing alkyltrimethylammonium chlorides or bromides with the same tail lengths. The value of TK ranged between 292 and 314 K and increased strongly with increase in the chain length of the hydrophobic tail. Micellization was described as both entropy and enthalpy-driven. Based on the direct calorimetry measurements, the general trends in the CMC with the temperature, hydrophobic tail length and NaCl addition were found to be similar to those of other types of cationic surfactants. The particularly exothermic character of micellization was ascribed to the hydrogen-binding capacity of the guanidinium head-group.

Nanoparticles (NPs) can now be synthesized with a wide array of controlled sizes, shapes, and properties. However, turning them into nanomaterials often requires packing them into ordered assemblies to manifest specific electronic or optical properties for applications in nanoelectronics, optics, and metamaterials. Colloidal self-assembly (1) of NPs is relatively simple but is often restricted to high-symmetry crystals by the lack of specific directional bonds, especially for dilute NP solutions. To obtain lower symmetries that confer useful optical or electronic properties, long-range directional interactions must be imparted. On page 69 of this issue, Mundoor et al. (2) make clever use of an anisotropic host fluid, a liquid crystal, to promote the formation of a low-symmetry crystal in a dilute dispersion of nanorods.

The phenomenon of complexation between oppositely charged colloids or macromolecules in aqueous solution is a fundamental process, widely exploited by nature, as for example in DNA packaging within biological cells [2], but also by technology, as in industrial colloidal stabilization, water treatment and paper making [3].Being the result of a delicate balance of forces of different nature, small variations in the physico-chemical parameters may induce large changes in the resulting complexes [4]. Electrostatics is clearly the relevant interaction in driving the aggregation, although non-electrostatic interactions can be important in modulating the process and can deeply affect the characteristics of the resulting self-assembled structures. However, despite the intense experimental, theoretical and computational research aimed to understand the mechanisms driving the formation and the stabilization of the complexes [5], [6] and [7] in the physical context of macroion-multivalent counterion interactions [8], due to the great complexity of these systems, also the details of purely electrostatic interactions remain to be completely clarified.The possibility to get a fine control of the stability of the complexes by tuning the competition between attractive and repulsive electrostatic interactions justifies the actual enduring attention on polyion–colloid complexation, being key to the technological development of nano-structured materials or nano-devices to be used for example in drug delivery or gene-therapy [9] and [10].In particular, a rich literature exists on the variety of structures formed by charged liposomes interacting via electrostatic forces with oppositely charged linear polyions, whether they are synthetic polymers, polypeptides or DNA [11], [12] and [13]. A feature characterizing the phase behavior of these systems is the presence of a “reentrant condensation” accompanied by a marked “overcharging”, or charge inversion [14] and [15]. Indeed, when a given volume of a liposome suspension is mixed with the same volume of a solution containing oppositely charged polyelectrolytes, the complexation is systematically observed due to a rapid adsorption of polyelectrolytes chains at the liposome surface, forming what we have defined as “polyelectrolyte-decorated particles” (hereafter pd-particles), followed by their aggregation in pd–liposome clusters, as it is schematically represented in panel A of Fig. 1. For low enough polyelectrolyte concentration the clusters are small (they are formed by a few liposomes), after their rapid formation they are very stable, their measured ζ-potential being only slightly lower, in absolute value, than that measured for the liposomes in the absence of adsorbed polyelectrolytes. As the polyion concentration (and hence the ratio, ξ, between the number of stoichiometric charges on the polymer and on the particles) is increased, larger but still stable clusters are formed, with a ζ-potential which is further reduced in absolute value. At a sufficiently high polyelectrolyte concentration, the liposome suspension is completely destabilized, the large clusters that form are not stable, their ζ-potential is close to zero and they rapidly coalesce in macroscopic “flocs”. Going beyond the isoelectric point, hence further increasing the polyelectrolyte concentration, stable clusters form again, but now their size decreases upon increasing the polyelectrolyte concentration in the mixture: the polyelectrolyte-induced condensation of the liposomes is hence “reentrant”. At the same time, the ζ-potential after having passed through the zero, increases again in absolute value, and the sign of the excess charge of the clusters is that of the polyelectrolyte, i.e. opposite to that of the original liposomes (charge inversion).

Several techniques to assemble artificial lipid bilayers involve the zipping of monolayers. Theirefficiency is determined by the renewal of the saturated monolayers to be zipped and this proceeds byadsorption of lipids dispersed in oil as aggregates. The size of these lipids aggregates is a key parameterto ensure both the stability of the suspension and a fast release of lipids at the interface. We proposea new method inspired from the solvent-shifting nucleation process allowing to control and tune thelipid aggregates size and that improves the production of artificial membranes. It is simpler and fasterthan current methods starting from a dry lipid film, which are highly sensitive to environmental conditions.This method opens the route to bilayer production processes with new potentialities in membranecomposition.

Structuring wheat gluten proteins into gels with tunable mechanical properties would provide more versatility for the production of plant protein-rich food products. Gluten, a strongly elastic protein material insoluble in water, is hardly processable. We use a novel fractionation procedure allowing the isolation from gluten of a water/ethanol soluble protein blend, enriched in glutenin polymers at an unprecedented high ratio (50%). We investigate here the viscoelasticity of suspensions of the protein blend in a water/ethanol (50/50 v/v) solvent, and show that, over a wide range of concentrations, they undergo a spontaneous gelation driven by hydrogen bonding. We successfully rationalize our data using percolation models and relate the viscoelasticity of the gels to their fractal dimension measured by scattering techniques. The gluten gels display self-healing properties and their elastic plateaus cover several decades, from 0.01 to 10,000 Pa. In particular very soft gels as compared to standard hydrated gluten can be produced.