Effect of Geometry on Packing and Parking of Colloidal Spheres
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CitationTanjeem, Nabila. 2020. Effect of Geometry on Packing and Parking of Colloidal Spheres. Doctoral dissertation, Harvard University, Graduate School of Arts & Sciences.
AbstractColloidal microspheres, sometimes referred to as `model atoms,' are commonly used to elucidate self-assembly mechanisms of different materials. One of the important yet relatively unexplored parameters that affects self-assembly is the geometry of the substrate on which self-assembly takes place. In this thesis, I examine how substrate geometry affects self-assembled structures and self-assembly dynamics and demonstrate how this knowledge can be used to design precisely controlled nanostructures.
Colloidal self-assembly can be designed in various ways -- weak attractive interactions between colloidal microspheres give rise to colloidal crystallization, whereas strong attractive interactions result in random sequential adsorption. I show a number of methods to tune collloidal interactions to achieve crystallization (packing) and random sequential adsorption (parking) on the surface of a cylinder. A cylinder has a a zero Gaussian curvature, but a non-zero mean curvature and a finite circumference. Using experiment and theory, we demonstrate that the finite circumference and mean curvature of a cylindrical substrate affect both crystallization and random parking of colloidal spheres.
A crystal that completely wraps around a cylindrical surface must contend with closure. We find that the closure constraint gives rise to unique structural features, such as chirality, line-slip defects, and kinked line-slip defects with fractional vacancies. We show that the morphology of these structures arises from the crystallization dynamics. When colloidal spheres randomly adsorb on a cylindrical substrate, we find that the surface coverage fraction becomes a function of the curvature of the cylinder and deviates significantly from the surface coverage fraction on a flat substrate. Both of these findings provide a pathway to realize self-assembly mechanisms of natural and artificial tubular structures.
Finally, we show that sphere packing on a spherical substrate can be used to synthesize patchy colloidal structures. We turn the patchy structures into octahedral plasmonic nanoclusters using a multi-step synthesis approach. We find that these nanoclusters have identical optical properties, which indicates robust and precise control over their geometry. This result shows that what we learn from colloidal self-assembly and geometry can be applied to design materials with complex structures and functionality.
Citable link to this pagehttps://nrs.harvard.edu/URN-3:HUL.INSTREPOS:37365124
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