Crossing free-energy barriers: Nucleation in complex colloidal and biological systems

Nucleation is one of the most common and important processes in our lives. It not only plays a crucial role in many biological processes within our cells, but is also essential for the production of everyday products such as chocolate, toothpaste, and medicines. In short, nucleation is the process by which a phase transition, such as freezing or evaporation, begins by first forming a small amount of the new phase, which then continues to grow. For example, think of the formation of small ice crystals when water freezes, or the gas bubbles that appear when water starts to boil. The goal of my PhD research is to gain a better fundamental understanding of nucleation and address several open questions surrounding this process. For this, we delve into the theory behind crystal nucleation and determine the effect of the interface between the fluid phase and the crystal phase. Additionally, we study the nucleation of different systems to gain better insight into the precise onset of nucleation. To this end, I use computer simulations and primarily focus on crystal nucleation in colloidal systems. These systems consist of microscopic particles, called colloids, with sizes ranging from tens of nanometers to a few micrometers, which move freely in a solvent. I investigate whether we can predict where in the fluid phase the crystal will form. Knowledge of this can help control nucleation more precisely, for example, in the production of substances such as medicines. Finally, I study an example of nucleation in a biological system, specifically the compaction of HIV DNA under the influence of a protein called HIV integrase. This contributes to a better understanding of a crucial step in the HIV life cycle, which can aid in the more targeted development of medications.