Nano Droplets: The Impact of pH and Ionic Strength

What happens when you mix water, ethanol, and trans-anethol? You get a special type of liquid mix called a surfactant-free microemulsion. These mixtures are interesting because they can form tiny clusters, or nanodomains, without needing any extra helpers, like surfactants. The key to understanding these nanodomains is looking at how they form and stay stable. This was done by tweaking the mix with different amounts of ions and varying the pH levels. The results showed that extreme pH levels and high ionic strength have a big impact on how these nanodomains grow and behave. In water-based structures, extreme pH levels led to larger nanodomains with fewer of them. On the other hand, oil-based structures stayed pretty much the same. This behavior is due to a process called Ostwald ripening, where bigger droplets grow at the expense of smaller ones. Both calculations and experiments showed that this ripening process is heavily influenced by very acidic or very alkaline conditions. In a neutral environment, electrostatic repulsion plays a crucial role. It prevents the droplets from sticking together when they collide. This insight is valuable for various applications, such as creating new materials, dissolving drugs, and making gels. Understanding how to control these nanodomains can lead to better and more efficient processes in these fields. One important thing to note is that the stability of these nanodomains is not just about their size. It is also about how they interact with each other. By controlling the pH and ionic strength, scientists can fine-tune these interactions to get the desired outcomes. This level of control opens up new possibilities for using surfactant-free microemulsions in practical applications.