Structures And Dynamics Of Self-assembly Of Non-spherical Colloidal Particles On Cylindrical Surfaces

Self-assembly of non-spherical colloidal particles becomes a hot topic recently,as the various structures and diverse functions that the assemblies possess.For example,it can potentially apply into the fields of sensing intelligent materials,optical band gap materials and energy storage materials.However,the assembled structures or phases of non-spherical colloidal particles have not been fully understood.Self-assembly of non-spherical colloidal particles on a curved surface is one of these unsolved problems.In this study,we fabricated platelet colloidal particles with square and equilateral triangle of faces(hereinafter referred to as square and triangle colloidal particles)by photolithography,and developed the tracking technology by microscope aiming at non-spherical colloidal particles on curved surfaces.We studied the self-assembly of square/triangle colloidal particles on a cylindrical surface using the tracking technology by microscope,and revealed the processes of the self-assembly structure and dynamic of non-spherical colloidal particles on a cylindrical surface.In this study,to understand the role that the geometric shape of the boundary plays on the diffusion of non-spherical colloidal particles,here we experimentally studied the diffusion of a single Brownian square colloidal particle on one of the simplest yet non-trivial substrate-a cylindrical surface in the presence of depletion attractions.By particle video tracking microscopy,we found that the translational motion of a square colloidal particle is diffusive along the axial direction of cylinder but sub-diffusive along the circumferential direction due to the confinement induced by gravity,while its rotational motion displays a sub-diffusive behavior due to the confinement induced by orientation-dependent depletion interactions.Such confinement effect decreases as the radius of curvature increases and can be tuned both through surface curvatures and/or depletion interactions.Our results not only help us understand the effect of geometric shape of the surface on particle diffusion,but also provide a new way to control the dynamics of anisotropic particles through curved surfaces in the presence of depletion attractions.Then,we experimentally investigated the self-assembly of micron-sized Brownian hard square colloidal particles on a curved cylindrical surface for the first time.We found different self-assembled structures in tubes having different radii.Specifically,at higherφ_A rhombic crystal structures are observed in all tested tubes;whereas,at lowerφ_A hexagonal rotator crystal structures are observed for all but the smallest tube radius,which instead exhibits a tetratic phase.We show that this transition is caused by the curvature-induced orientation-dependence of the depletion attraction between the square colloidal particles and the underlying cylindrical surface,which is used to form a monolayer of square colloidal particles above the cylindrical surface.Defects,such as twinning and dislocations,are also observed and discussed.Our results demonstrate a way towards control over the self-assembly of anisotropic particles through curvature and depletion-attraction-induced orientational confinement.In addition,the system employed in this work also provides a basic model for further understanding the shape-curvature physics that could be embedded in certain biological problems,such as the growth of cell walls.Finally,we obtained a good single crystal with honeycomb lattice structures through assembling of triangles on cylindrical surfaces,which is fewer defects formed on the cylindrical surface with larger curvature.Different from the self-assembly behavior of triangles on the flat plane(they can only form liquid phase and triatic liquid crystal phase),honeycomb lattice crystals can be obtained at a high fraction area in all tubes when triangles self-assemble on the cylinder.As the radius of curvature of the cylinder decreases,the defects in the system decrease.This provides a new way to fabricate new material with honeycomb lattice structures.In conclusion,we developed and completed the micro-tracking technology of non-spherical particles on the cylindrical surface by using square and triangular colloidal particles as model system,and elucidated the relationship between the self-assembly structure and the size of the colloidal particles and the radius of the cylinder by studying the square and triangle colloidal particles on the cylinder and plane(as control).Illustrates the different shapes of colloidal particles formed different self-assembled structures and dynamics.For further research,the regular polygon colloidal particles on the cylinder of self-assembly and explore the particle’s shape on the surface of self-assembly which lays a foundation for the development and application of self-assembly of non-spherical colloidal particles on the curved surface.This study will promote our understanding of the law of non-spherical colloidal particles self-assembly on curved surfaces,improve the theory of colloidal condensed matter,and provide a theoretical basis and experimental basis for the development of self-assembly technology of metamaterials.