Assemble Nanodumbbells Into Superstructures Andexplore The Mechanism

Self-assembled materials show excellent optical,magnetic,and mechanical properties compared with traditional materials,and thus have become research hotspots in the fields of physics,chemistry,and biology.Research on self-assembling materials can help design and produce novel and functional materials.Self-assembled materials show characteristics that their property depends on the structure of material.Therefore,for a long time,the center research direction of self-assembly is to enrich the assembly structure.Compared with bulk materials,nanomaterials display advantages such as large specific surface area and size effect,and always exhibit different characteristics from bulk materials.Therefore,it is of great significance to study the self-assembly of nanoparticles.As it known to us that nanoparticles of different shapes are usually assembled into different structures.Anisotropic nanoparticles show anisotropic forces and can often be assembled into a variety of assembly structures.The self-assembly of anisotropic nanoparticles with common morphology,such as cubic morphology and cubic octahedron,has been much.However,the self-assembly of nanoparticles with complex morphology is still less studied.Rare earth up-converted nanoparticles have excellent optical properties due to their special electronic structure and have been used in the fields of bioimaging,biotherapeutics,and photovoltaic devices.Studying the self-assembly structure of rare earth up-conversion nanoparticles is a promising way to improve the optical,mechanical,and magnetic properties of materials.Meanwhile,with the development of nano-synthesis technology,it is possible to prepare rare earth upconversion nanoparticles with controlled morphology and size,making rare earth upconversion nanoparticles an ideal building block for self-assembly investigation.Based on this,high-quality dumbbell-shaped β-Na YF4: 18% Yb,2% Er @ Na Gd F4 core-shell nanocrystals were prepared by thermal decomposition method in this paper.By changing the ratio of the reactants Na OH and NH4 F,dumbbell-shaped nanoparticles with different size aspect ratios can be obtained.Subsequently,the self-assembly structure and assembly mechanism of dumbbell-shaped nanoparticles were systematically studied.First,a monolayer assembly film of nanodumbbells was prepared by evaporating a certain concentration of nano-dumbbell colloidal solution at the glycol interface,and the structure was determined by characterization of real space and reciprocal space.It turns out that the structure shows a special orientational order,that is,the nanodumbbells are close-packed with a rotation angle of 120 degrees.Further analysis shows that this assembly structure is determined by the spherical and rod-shaped geometric feature of nanodumbbells.This not only enriches the assembly structure but also deepens the understanding of the effect of anisotropic nanoparticle morphology on assembly.In addition,theoretical research predicts that the multi-void structure resulting from this arrangement is expected to improve the mechanical properties of the material and the performance of piezoelectric materials.Second,by increasing the concentration of the dumbbell colloid solution,an ordered two-layer assembly structure can be prepared.Similar analysis shows that this two-layer assembly structure can be regarded as a stack of two single-layer structures with similar structure.The shape of the concave middle part of the nanodumbbell and the convex head are complementary,which helps stabilize this two-layer structure.Third,if the concentration of the nanodumbbell colloidal solution is further increased,moiré patterns can be obtained,in which the two layers are relatively rotated at a certain angle.Fourth,if chang the size aspect ratio of the nanodumbbells and the assembly subphase,the orientation of the nanodumbbells can be controlled from a horizontal arrangement to an upwardly tilted and vertical arrangement.Finally,we provide a method to preparing nanodumbbell superparticles,namely the microemulsion method.The arrangement of the nanodumbbells in the superparticles has been analyzed,which provides another way of thought for preparing the three-dimensional assembly structure of the nanodumbbells and enriches the assembly structure of the nanodumbbells.This study not only enrich the complexity of superstructures assembled from nanodumbbells,but also provide another way to design novel nano-assemblies.Meanwhile,this study will spur applications of nanodumbbells assemblies.