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Biosurfactants represent an ecosustainable alternative to conventional surfactants, allowing to reduce the environmental impact arising from the increasing production of industrial surfactant-containing formulations. In the present work, the physico-chemical properties of the aqueous solutions of rhamnolipids (Rha) are compared to those of sodium lauryl ether sulfate (SLES), a widely used surfactant in many applications. Moreover, in view of a possible partial replacement, mixtures of these surfactants are analyzed. The surfactant self-aggregation in bulk solution is investigated by surface tension, dynamic light scattering (DLS) and electron paramagnetic resonance (EPR), finding that Rha and SLES form mixed aggregates whose morphology, dimension and internal structure depend on the composition of the mixture. An increase of the Rha content induces the formation of large micelles, with a compact inner core. A nonideal behavior of Rha-SLES mixtures is found, indicating antagonistic interactions between the two surfactants. Contact angle, emulsification and foaming measurements are carried out to investigate the functional behavior of the surfactant aqueous mixtures at the interface with solids, oil and air. Rha improves the wettability of hydrophobic surfaces but decreases the emulsion stability and the foamability. The results of the different experimental techniques are rationalized in a framework based on the molecular architectures, highlighting that the balance between the flexibility of the SLES headgroups and the bulkiness of the Rha ones allow tuning the mixture behavior, both in bulk and at the interfaces. Understanding the relationship between the physico-chemical properties of these mixtures and their functional behavior is strategic to steer the rational exploitation of Rha in green chemical formulations. In this direction, a comparative ecotoxicological assay is finally presented, whose results demonstrate the better profile of Rha compared to SLES.

In polymer processing as fibre spinning, injection moulding, film casting and so on, the forming phase of the melt is followed by its solidification due to cooling. This implies the crystallization of the polymer during the processing. Typically, crystallites are formed and an ordered structure can be detected, if the cooling rate is not too high. As a consequence, during processing the rheological response of the material significantly changes from a liquid-like to a solid-like behaviour. The knowledge of the mechanical response of the material during crystallization is therefore of seminal importance for process control and modelling. We here focus on a random copolymer, the Ethylene vinyl acetate (EVA), made of ethylene and varying amounts of vinyl acetate that interfere with poly-ethylene chain packing reducing the crystallinity, improving the transparency and lowering the melting temperature. This allows studying the crystallization kinetics at relatively low temperatures so to avoid all the experimental issues related to thermal degradation. The crystallization process is rheologically studied in non-isothermal conditions and the frequency spectra are measured at different temperatures to investigate the viscoelasticity of EVA during the change of phase. Coupling the crystallization kinetics and the viscoelastic spectra at different temperatures, i.e. at different degree of crystallinity, we determine two independent shift factors, one for the time-crystallinity shift, the other for the time-temperature shift, so to propose a new time-temperature-crystallinity superposition to reconcile all the data on a single master curve. In this way, the experimentally observable frequency range has been widen significantly so to detect all the relaxation times of the material from the shortest to the largest ones.

Diffusion plays a central part in many unit operations. The Maxwell–Stefan model is the dominant model for both gaseous and liquid diffusion. However, it was developed from the kinetic theory of gases, raising the question of whether it can be extended to non-ideal liquid systems. The dynamic fluctuation model is an alternative model based on the Cussler theory and predicts a smaller thermodynamic influence relative to the linear influence of the Maxwell–Stefan model due to dynamic concentration fluctuations. Since the dynamic fluctuation model, which uses the scaling factor α, had improved performance relative to the Maxwell–Stefan model for a wide range of binary systems, it is postulated that this improved performance should also be observed for a ternary system. In this work, the dynamic molecular fluctuation model was extended to a highly non-ideal ternary system, using the same scaling factor α, through matrix manipulation. Using self-diffusion data measured by NMR, mutual diffusion predictions of the developed model and the Maxwell–Stefan model were compared to experimental mutual diffusion data of the partially miscible system ethanol/toluene/n-decane. It is demonstrated that the dynamic fluctuation model gives improved predictions relative to the Maxwell–Stefan approach, consistent with previous observations on binary systems, showing that the reduced thermodynamic influence of the dynamic fluctuation model is an improvement. In addition, we show that the use of local mole fractions, to account for molecular association, in both the dynamic fluctuation and Maxwell–Stefan models, results in improved diffusion predictions for the ternary system. The results confirm that the dynamic fluctuation model improves predictions of mutual diffusion in liquid mixtures, suggesting a non-linear correction to the thermodynamic correction factor. The results also suggest that that the key assumptions in the Maxwell–Stefan model and its derivation, rooted in the kinetic theory of gases, are not entirely accurate for highly non-ideal liquid systems. The optimum α for the ternary system studied here is approximately 0.45, similarly to the optimum α of 0.40 to 0.80 for a range of binary systems previously studied, suggesting that the use of the α scaling factor, which is grounded in scaling laws theory, is of general validity.

The diffusion coefficients of the ternary system pentaethylene glycol-triethylene glycol-water have been measured at five compositions at constant total solute concentration. A theory that is an extension of the current hydrodynamic equations for calculation of Dij has been tested on this ternary system. These equations use values of what we will refer as the `effective' volumes of the solutes. These volumes were obtained by the analysis of the diffusion coefficients of the two corresponding binary systems. The agreement between theory and the experimental values for the main-term diffusion coefficients Dii is quite good and the agreement between the predicted and measured cross-term diffusion coefficients Dij (i≠j) is very encouraging. The solute-solute nonbonding interactions seem not to have a significant effect on the diffusion coefficients in our experimental conditions.