Polyelectrolyte-surfactant complexes (PESCs) are important soft colloids with applications in the field of personal care, cosmetics, pharmaceutics and much else. If their phase diagrams have long been studied under pseudo-equilibrium conditions, and often inside the micellar or vesicular regions, understanding the effect of non-equilibrium conditions, applied at phase boundaries, on the structure of PESCs generates an increasing interest. In this work we cross the micelle-vesicle and micelle-fiber phase boundaries in an isocompositional surfactantpolyelectrolyte aqueous system through a continuous and rapid variation of pH. We employ two microbial glycolipid biosurfactants in the presence of polyamines, both systems being characterized by their responsiveness to pH. We show that complex coacervates (Co) are always formed in the micellar region of both glycolpids' phase diagram and that their phase behaviour drives the PESCs stability and structure. However, for glycolipid forming single-wall vesicles, we observe an isostructural and isodimensional transition between complex coacervates and a multilamellar walls vesicle (MLWV) phase. For the fiber-forming glycolipid, on the contrary, the complex coacervate disassembles into free polyelecrolyte coexisting with the equilibrium fiber phase. Last but not least, this work also demonstrates the use of microbial glycolipid biosurfactants in the development of sustainable PESCs.

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Understanding the colloidal stability and aggregation behavior of TiO2 nanoparticles in aqueous suspension is a prerequisite to tune supracolloidal structure formation. While the aggregation mechanism for dried TiO2 nanopowders is well documented, there is still work to be done to understand TiO2 nanoparticle aggregation in suspension. Therefore, this work focuses on the colloidal stability and aggregation mechanism of TiO2 nanoparticle aqueous suspensions prepared using a straightforward one-step sol–gel-based approach over a concentration range of 0.5–5 wt %. Fully crystalline nanoparticles consisting primarily of anatase were obtained. After assessing the colloidal stability of the as-prepared suspensions, small-angle X-ray scattering coupled with fractal analysis was carried out. This analysis showed, for the first time, how the TiO2 nanoparticle aggregation mechanismpredicted by the diffusion limited cluster–cluster aggregation (DLCA) and diffusion limited particle–cluster aggregation (DLA) theoriesdepends directly on the starting concentration in the aqueous suspensions. We found that concentrated suspensions favored DLA, while dilute suspensions tend to follow the DLCA mechanism. The effect of the aggregation mechanism on the aggregate shape is also discussed.

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