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Two series of sugar esters with alkyl chain lengths varying from 5 to 12 carbon atoms, and with a head group consisting of glucose or galactose moieties, were synthesized. Equilibrium surface tension isotherms were measured, yielding critical micellar concentration (CMC) surface tensions at CMC (γcmc) and minimum areas at the air–water interface (Amin). In addition, Krafft temperatures (Tks) were measured to characterize the ability of molecules to dissolve in water, which is essential in numerous applications. As a comparison to widely used commercial sugar-based surfactants, those measurements were also carried out for four octyl d-glycosides. Impacts of the linkages between polar and lipophilic moieties, alkyl chain lengths, and the nature of the sugar head group on the measured properties were highlighted. Higher Tk and, thus, lower dissolution ability, were found for methyl 6-O-acyl-d-glucopyranosides. CMC and γcmc decreased with the alkyl chain lengths in both cases, but Amin did not appear to be influenced. Both γcmc and Amin appeared independent of the ester group orientation. Notably, alkyl (methyl α-d-glucopyranosid)uronates were found to result in noticeably lower CMC, possibly due to a closer distance between the carbonyl function and the head group. [ABSTRACT FROM AUTHOR]

Sugar-based surfactants are a class of environmentally-friendly surface-active molecules well known for their functional performances, good biodegradability and reduced ecological footprint. Many previous studies have explored the surface properties of these surfactants. However, very little research has investigated their foaming properties. The present study examines the foaming behavior of 17 nonionic sugar-based surfactants with gradual structure variation. Foaming properties such as foamability, foam stability and maximum foam density were measured using the gas-sparging method. The influence of surfactant structure and concentration on foaming properties was evaluated. The data on surface adsorption properties, determined in the previous study, and foaming properties were then analyzed using a Principal Component Analysis. It was shown that the foaming behavior of glycolipids can be correlated to concentration and interfacial properties. Predictive models are proposed to anticipate the foaming behavior and provide a useful guide for screening the foamability of bio-based surfactants in various technological applications. [ABSTRACT FROM AUTHOR]

The evolution of W/O emulsion versus time in microgravity conditions has been studied in the framework of the FASES (Fundamental and Applied Studies on Emulsion Stability) project sponsored by the European Space Agency (ESA). The objective of this study was to investigate the evolution of W/O emulsions made of water + paraffin oil + SPAN 80® under purely diffusive conditions (no gravity driven effects) and to compare with evolution of similar emulsions observed on ground. A correlation between the state of dispersion of water and either the freezing temperature during cooling, or the freezing time at a fixed temperature was used to follow the emulsion evolution versus time. For that purpose, two identical calorimeters were built by Airbus (formerly EADS) with the support of the French company SETARAM: The Flight Model (FM) located onboard the International Space Station (ISS) and the Engineering Model (EM) located at the TELESPAZIO Centre in Naples. Dedicated cells were filled on ground with different formulations of W/O emulsions and identical experiments were performed with the FM and the EM models in order to highlight the differences in emulsion evolution. On ground, the experiments were performed by cooling and heating the calorimeter between 40 °C and −60 °C but due to technical constraints in the FM, the experiments performed in the FSL (Fluid Science Laboratory) of the ISS were limited to a lowest temperature of −22 °C. The results obtained with the FM confirmed the formation of emulsions in the dedicated cell with the selected stirring system in space. These results also demonstrated that it is possible to detect the freezing and the melting of the water droplets with the designed calorimeter either during cooling and heating phases or versus time during a temperature holding period at −22 °C. Furthermore, the comparison between both results obtained with the EM on ground and with the FM in space revealed distinct behaviours. This study drove us to focus on other mechanisms than sedimentation and convection to account for the destabilization of these kinds of emulsions.

Foaming properties of five model surfactants, namely, sodium laureth sulfate (SLES), sodium dodecylsulfate (SDS), polyoxyethylene 23 lauryl ether (Brij L23), polysorbate 20 (Tween 20), and polysorbate 80 (Tween 80), have been compared as a function of experimental conditions using the gas‐sparging method. The influence of surfactant concentration relative to the critical micelle concentration (CMC) and three process parameters—frit porosity, gas flow rate, and preset volume of foam (or bubbling time)—was studied by means of a 24–1 factorial design. Three foaming properties were considered: foam capacity, foam stability, and maximal foam density. At the CMC, SLES, SDS, Tween 20, and Brij L23 were indistinguishable, all having very high foaming capacity and stability, regardless of process conditions. At 0.1 CMC, differences among them were highlighted especially at the lowest frit porosity coupled to the highest gas flow rate. Those conditions are thus recommended when a rapid screening of surfactant foaming performances is needed. [ABSTRACT FROM AUTHOR]