Nano-droplet formation in water/ethanol or isopropanol/mosquito repellent formulations

• Nano-structures were found in water/alcohol/mosquito repellent systems.
• DLS/SLS confirmed findings for both natural and synthetic repellents.
• Nano-structures can be found in commercial formulations.
• Potential consequences for formulation efficacy.

It was recently demonstrated that nano-structures were present in water/ethanol/oil systems, where the oil was either octanol or fragrance molecules. The goal of the present work is to check if such structures exist also in other, related systems and if a general concept can be deduced from these observations. To this purpose, natural and synthetic mosquito repellent molecules were investigated, which represent nearly all repellents used on the market. For the ternary water/alcohol (ethanol or isopropanol)/repellent systems ternary phase diagrams were established. The presence and the ordering of the nano-droplets were checked and characterized with dynamic and static light scattering and conductivity measurements. Based on these results it can be concluded that a nano-ordering with generally an organic continuum exists in hydro-alcoholic commercial mosquito repellents, and thus that these systems are not simply molecular solutions. This might have a consequence for diffusion processes in the skin.

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