This study reports on the effects of conformationally controlled amphiphilicity of antimicrobial peptides (AMPs) on their ability to coat TiO2 nanoparticles (NPs) and boost the photocatalytic antimicrobial effects of such NPs. For this, TiO2 NPs were combined with AMP EFK17 (EFKRIVQRIKDFLRNLV), displaying a disordered conformation in aqueous solution but helix formation on interaction with bacterial membranes. The membrane-bound helix is amphiphilic, with all polar and charged amino acid residues located at one side and all non-polar and hydrophobic residues on the other. In contrast, the d-enantiomer variant EFK17-d (E(dF)KR(dI)VQR(dI)KD(dF)LRNLV) is unable to form the amphiphilic helix on bacterial membrane interaction, whereas the W-residues in EFK17-W (EWKRWVQRWKDFLRNLV) boost hydrophobic interactions of the amphiphilic helix. Circular dichroism results showed the effects displayed for the free peptide, to also be present for peptide-coated TiO2 NPs, causing peptide binding to decrease in the order EFK17-W > EFK17 > EFK17-d. Notably, the formation of reactive oxygen species (ROS) by the TiO2 NPs was essentially unaffected by the presence of peptide coating, for all the peptides investigated, and the coatings stabilized over hours of UV exposure. Photocatalytic membrane degradation from TiO2 NPs coated with EFK17-W and EFK17 was promoted for bacteria-like model bilayers containing anionic phosphatidylglycerol but suppressed in mammalian-like bilayers formed by zwitterionic phosphatidylcholine and cholesterol. Structural aspects of these effects were further investigated by neutron reflectometry with clear variations observed between the bacteria- and mammalian-like model bilayers for the three peptides. Mirroring these results in bacteria-like model membranes, combining TiO2 NPs with EFK17-W and EFK17, but not with non-adsorbing EFK17-d, resulted in boosted antimicrobial effects of the resulting cationic composite NPs already in darkness, effects enhanced further on UV illumination.

Green surfactants, categorized as biobased and biosurfactants, pose formulation challenges due to their compositional variability and biodegradability. Our work addresses these challenges in formulating a hard surface cleaning spray. We utilize glucamide surfactants with a high renewable carbon index (RCI=95 %), incorporating limonene as both solvent and perfume. Additionally, the concept of formulating a concentrated "juice" is explored. A partial phase diagram guides our formulations, and rheology and small angle X-ray scattering (SAXS) pinpoint the optimal dilution line. Our concentrated formula exhibits liquid crystalline phases, offering potential applications in gel-like tablets. Performance evaluations against a market product reveal mixed results, indicating the need for further optimization. The study emphasizes a formulation minimalism approach, aligning with modern trends. It showcases the potential of green surfactants, providing insights into their behavior under varying concentrations and paving the way for environmentally friendly cleaning solutions.

Recently a new, time saving, approach to the determination of the composition at which a microemulsion is balanced has been developed using the so called HLD-titration. The key of the method is the observation that in correspondence of the balanced state where the microemulsion coexist with excess oil and water (Winsor III phase equilibrium), the level reached by the three-phasic system under stirring has a consistent maximum allowing a fast and low-cost readout of the balanced state that permits the evaluation of the surfactants characteristic parameters (SCPs). To better understand how the formation of a balanced microemulsion is related to rheology, here a titration experimental approach was adopted under turbulent flow meanwhile fluid friction. A mixture of equal volumes of brine and oil and didodecyldimethylammonium bromide (DDAB) is titrated with dodecyltrimethylammonium bromide (LTAB), in the Couette cell of a rheometer under continuous rotation, promoting the transition from a Winsor II (w/o microemulsion coexisting with brine) to a Winsor III phase equilibrium. The turbulent apparent viscosity was measured after each addition of the LTAB. We demonstrate that the turbulent apparent viscosity attains a minimum at the Winsor III phase equilibrium. Furthermore, we have investigated the microstructural evolution of the microemulsions found at the different DDAB/LTAB ratios that reproduces the HLD-titration by means of small-angle X-ray scattering (SAXS) and diffusion nuclear magnetic resonance (NMR) and rheo- small-angle light scattering (rheo-SALS). The anisotropy index, measured by rheo-SALS, increases upon increasing the shear rate suggesting the ability of oil and water domains, in the balanced state, to elongate along the streamlines.

The Hydrophilic-Lipophilic Difference (HLD) model can be described by additive contributions accounting for the effect of the oil and surfactant nature, temperature, ionic strength, and so on. The first step to build an HLD framework for a surfactant class is to have Winsor III phase equilibria in a restricted range of formulation variables. In this respect, anionic and nonionic surfactants are well suited for an HLD study. On the contrary, it is difficult achieve for pure cationic surfactant Winsor III phase equilibria without the addition of alcohols and this has precluded the extension of the HLD to cationic surfactants.

In the present contribution, we first propose a system based on a blend of single-tailed and double-tailed cationic surfactant to study the oil contribution, and then we afforded the determination of the surfactant contribution trough an experimental approach (the “HLD-titration”) that is especially tailored for systems displaying a wide range of existence of Winsor III phase equilibria.

HLD-titration results confirmed the ionic strength contribution to HLD as a logarithmic function of salinity for cationic-based microemulsions similarly to anionic ones. However, the oil carbon number contribution is almost four-fold larger (k ​= ​0.7 ​± ​0.1) with respect to anionic surfactants. A clearing point was observed in correspondence of the Winsor III phase equilibria under stirring. This approach allows us the determination of the so-called characteristic curvature (Cc), i.e. the term describing the surfactant nature contribution to the film curvature, of the cationic surfactant. Finally, the method was adopted to determine Cc values of 7 quaternary ammonium surfactants differing in the polar heads nature and further three amine oxide surfactant at pH ​= ​1 where they are protonated.

Microemulsions are thermodynamically stable, transparent, isotropic single-phase mixtures of two immiscible liquids stabilized by surfactants (and possibly other compounds). The assortment of very different microstructures behind such a univocal macroscopic definition is presented together with the experimental approaches to their determination. This tutorial review includes a necessary overview of the microemulsion phase behavior including the effect of temperature and salinity and of the features of living polymerlike micelles and living networks. Once these key learning points have been acquired, the different theoretical models proposed to rationalize the microemulsion microstructures are reviewed. The focus is on the use of these models as a rationale for the formulation of microemulsions with suitable features. Finally, current achievements and challenges of the use of microemulsions are reviewed.