Stable and temperature-responsive surfactant-free foamulsions with high oil-volume fraction.

There is more than foam: Optical microscopy images (with false colouring, see picture) depicting quick destabilization (within minutes) of foamulsions due to the coalescence of densely-packed oil droplets when heated at higher temperatures (65 °C).

Self-assembled bilayers from the protein HFBII hydrophobin: nature of the adhesion energy.

The hydrophobins are a class of amphiphilic proteins which spontaneously adsorb at the air/water interface and form elastic membranes of high mechanical strength as compared to other proteins. The mechanism of hydrophobin adhesion is of interest for fungal biology and for various applications in electronics, medicine, and food industry. We established that the drainage of free foam films formed from HFBII hydrophobin solutions ends with the appearance of a 6 nm thick film, which consists of two layers of protein molecules, that is, it is a self-assembled bilayer (S-bilayer), with hydrophilic domains pointing inward and hydrophobic domains pointing outward. Its formation is accompanied by a considerable energy gain, which is much greater than that typically observed with free liquid films. The experiments at different pH show that this attraction between the "hydrophilic" parts of the HFBII molecules is dominated by the short-range hydrophobic interaction rather than by the patch-charge electrostatic attraction.

Scaling behavior of delayed demixing, rheology, and microstructure of emulsions flocculated by depletion and bridging.

This paper describes an experimental comparison of microstructure, rheology, and demixing of bridging- and depletion-flocculated oil-in-water emulsions. Confocal scanning laser microscopy imaging showed that bridging-flocculated emulsions were heterogeneous over larger length scales than depletion-flocculated emulsions. As a consequence, G' as determined from diffusing wave spectroscopy (DWS) corresponded well with G' as measured macroscopically for the depletion-flocculated emulsions, but this correspondence was not found for the bridging-flocculated emulsions. The heterogeneity of bridging-flocculated emulsions was confirmed by DWS-echo measurements, indicating that their structure breaks up into large fragments upon oscillatory shear deformation larger than 1%. Depletion- and bridging-flocculated emulsions showed a different scaling of the storage modulus with the volume fraction of oil and a difference in percolation threshold volume fraction. These differences will be discussed on the basis of the two types of droplet-droplet interactions studied. Gravity-induced demixing occurred in both emulsions, but the demixing processes differed. After preparation of bridging-flocculated emulsions, serum immediately starts to separate, whereas depletion-flocculated systems at polysaccharide concentrations in the overlap regime usually showed a delay time before demixing. The delay time was found to scale with the network permeability, B; the viscosity, eta, of the aqueous phase; and the density difference between oil and water, Deltarho, as tdelay approximately B(-1)etaDeltarho(-1). The results are in line with the mechanism proposed by Starrs et al. (J. Phys.: Condens. Matter 2002, 14, 2485-2505), where erosion of the droplet network leads to widening of the channels within the droplet networks, facilitating drainage of liquid.

Depletion-flocculation in oil-in-water emulsions using fibrillar protein assemblies.

This paper shows that low concentrations of beta-lactoglobulin fibrils can induce depletion-flocculation in beta-lactoglobulin-stabilized oil-in-water emulsions. The minimum required fibril concentration for flocculation was determined experimentally for fibril lengths of about 3 and 0.1 microm. The minimum fibril concentration for flocculation is two orders of magnitude higher for the short fibrils than for the long ones. These experimental results correspond well with a theoretical prediction based on a model of spinodal decomposition. In addition, rheological measurements were performed, verifying that flocculation was induced by a depletion mechanism. The results of this study show that the minimum concentration required for depletion-flocculation can be tuned by varying the length of the fibrils.