Controlling Crystallisation Using Surface Topography

The use of heterogeneous nucleants to trigger crystallisation provides a means of controlling the size/structure of the crystals produced, where they form, and the induction time. However, with the exception of structural matching, there is little rationale for the identification of effective nucleants for many crystals. In this work, we explore the potential of using surface topography to direct crystal nucleation, where evidence is scattered across the literature that nucleation is promoted in features such as pits, pores and scratches. Substrates patterned with natural surface cracks are created in this study. These cracks spontaneously form in brittle materials whose surfaces are under strain. The cracked substrates are then coated with a thin film of a noble metal and chemically functionalised to optimise the surface chemistry. Controlling both the topography and surface chemistry of these substrates is shown to be highly effective in directing the nucleation of a range of substances including various inorganic and organic crystals. The origin and universality of this phenomenon is explored to determine how the topography and chemistry of a surface can promote the nucleation of a specific crystal. Controlling surface topography is therefore a valuable and frequently overlooked tool in controlling nucleation and can be used in the design of effective nucleants.