Nabila Tanjeem, Harvard University 

The curvature and topology of a substrate have significant impacts on self-assembly.  For example, previous research showed that colloidal crystals grown on the surface of a sphere are frustrated by its positive Gaussian Curvature and form ribbon-like domains. However, crystals can also be frustrated in the absence of Gaussian Curvature, but in the presence of a finite size constraint.  In this talk, I will present results of colloidal crystallization on the surface of a cylinder -- A cylinder has zero Gaussian Curvature, but a finite circumference which makes a crystal grown on it loop back and close itself. In experiment, we observe consequences of this closure constraint in the form of chirality and line-slip defects. For different cylinder-to-sphere size ratios, maximally packed crystals form with different chirality.  When a perfect crystal can not be accommodated, a special type of defect forms, known as a “line-slip defect”. We observe that the line-slip defects can take different shapes incorporating structural features like kinks and fractional vacancies. We explain the emergence of these features by considering the anisotropic crystal growth dynamics on the surface of a cylinder and show how defects with larger chiral angles can reach their equilibrium state faster. In another experiment, we explored the random sequential adsorption process on a cylinder and realized that when the system reaches jammed state, the surface coverage fraction deviates from that of on a flat surface and becomes a function of curvature. Finally, I will discuss some ongoing experiments exploring self-assembly on surfaces with negative Gaussian Curvature.