Adsorption of Equimolar Mixtures of Cationic and Anionic Surfactants at the Water/Hexane Interface

In mixed solutions of anionic and cationic surfactants, called catanionics, ion pairs are formed which behave like non-ionic surfactants with a much higher surface activity than the single components. In equimolar mixtures of NaCnSO4 and CmTAB, all surface-active ions are paired. For mixtures with n + m = const, the interfacial properties are rather similar. Catanionics containing one long-chain surfactant and one surfactant with medium chain length exhibit a strong increase in surface activity as compared with the single compounds. In contrast, catanionics of one mediumand one short chain surfactant have a surface activity similar to that of the medium-chain surfactant alone. Both the Frumkin model and the reorientation model describe the experimental equilibrium data equally well, while the adsorption kinetics of the mixed medium- and short-chain surfactants can be well described only with the reorientation model

Edible water barrier films prepared from aqueous dispersions of zein nanoparticles

Zein, a corn protein, is often used for preparing edible films and coatings. Since zein is insoluble in water, zein films and coatings are usually prepared by spraying or casting its aqueous ethanol solutions to a contact surface (Z(sol) films). However, the use of organic solvents in many food applications is unwanted. In this work, aqueous dispersions of zein nanoparticles were prepared by antisolvent precipitation from 90% v/v aqueous ethanol zein solutions. Zein films were then prepared by casting the dispersions in silicone molds and air-drying at 50 degrees C (Z(dis) films), The obtained films were characterized for morphology, FTIR analysis, mechanical, water barrier and optical properties, and were benchmarked against Z(sol) films. It was found that continuous zein films can be prepared out of aqueous dispersions of zein nanoparticles. Z(dis) films proved to have grainy morphology and higher surface roughness when compared to Z(sol). Surface roughness of Z(dis) films was decreased when plasticizer was added. Water barrier properties of Z(dis) films were found to be comparable to Z(sol) films. No differences in mechanical properties were found between Z(sol) and Z(dis) film. Size of zein particles influenced morphology and optical properties of zein dispersion films

Surface Tension Measurements with the Drop Profile Analysis Tensiometry—Consideration of the Surfactant Mass Balance in a Single Drop

In drop profile analysis tensiometry, the ratio of drop surfaces area S to volume V is large, i.e., S/V >> 1. In such a case, the concentration of a surfactant within the drop bulk decreases due to adsorption at the drop surface. In contrast, in bubble profile analysis tensiometry, we have S/V << 1 so that depletion due to adsorption is negligible. A protocol is presented to determine the correct adsorption parameters of surfactants from surface tension data measured by bubble and drop profile analysis tensiometry. The procedure is applied to experimental data measured for selected surfactants of different adsorption activities: C10OH, CTAB, Tween 20, and the equimolar mixture SDS + DoTAB. The results show that for surfactants with higher surface activity, the differences between the surface tensions measured with the drops and bubbles profile analysis tensiometry, respectively, are larger, while for less surface-active surfactants, such as SDS, the results obtained from drop and bubble profile experiments are very close. The correction procedure is based on the same set of adsorption parameters used to fit both the experimental data obtained from drop-based measurements (which involve the depletion effects) and those data measured in a way that depletion effects are negligible