Multi-level Self-Assembly Of Polymer Colloidal Crystals

With the development of polymer colloids preparation technology,anistropic polymer colloidal particles have become one of the most important building blocks to obtain ordered multifunctional materials.Colloidal crystals formed from polymer colloidal particles have been received extensive attention in recent years due to their promising applications in photonic crystals,drug delivery,and porous materials.The polymer patchy colloidal particles with both soft deformation and surface anisotropy have more unique physical and chemical properties,so can self-assemble to form novel micro/nano structures.Therefore,the polymer patchy colloidal particles provide a new idea for designing and obtaining colloidal crystals with specific functions.In this paper,we systematically study the multi-level self-assembly of polymer colloidal crystals.Firstly,the regulation law of obtaining soft patchy particles by self-assembly of block copolymers is explored.Secondly,we use one-component soft one-patch colloidal particles systems to self-assemble two-dimensional colloidal crystals and three-dimensional complex colloidal cluster crystals.Finally,the colloidal cubic diamond photonic crystals are obtained by utilizing cooperative self-assembly of a two-component system of two-patch colloidal particles and isotropic colloidal spheres.We also reveal the kinetic mechanisms of formation of these colloidal crystals.The specific research contents are as follows:Self-assembly of soft patchy particles based on block copolymers:Soft patchy particles with surface anisotropy are one of the most important building blocks for assembling nanostructures.Self-assembly of block copolymer is a relatively simple and convenient method to fabricate soft patchy particles.We use dissipative particle dynamics to study the regulation law of fabrication soft patchy colloidal particles using diblock copolymers.Our simulations results show that with decreasing solvent quality,the small crew-cut micelles merge to form a large crew-cut micelle.With further decreasing of the solvent quality,the patch-forming blocks gradually aggregated to form discrete patches on the micelle surface in order to reduce the unfavorable contact with the solvent and the micelle core.And we found that the number of patches is controlled by the composition of the block copolymer,the particles have less patches on the surface with a higher volume fraction of patchy-forming blocks.Multiple 2D crystal structures from direct self-assembly of soft one-patch particles:It has been found that soft colloids can form abundant crystal structures in 2D.How to obtain 2D crystals through direct self-assembly of 3D colloidal systems is an important issue.We observed abundant 2D crystals within layers of the bilayered lamellar phase by direct self-assembly of polymer soft one-patch(Janus)colloidal particles through a large number of molecular dynamics simulations.By tuning the density of the system,abundant highly-ordered 2D crystal structures including σ phase and kagome lattice are found in each layer of the bilayered lamellar phase.Our results of kinetics simulation show that these 2D crystal structures within these layers are formed simultaneously with the formation of the layers.The formation kinetics of these 2D crystals follow two different nucleation mechanisms,classical one-step nucleation mechanism represented by the σ phase,and two-step nucleation mechanism represented by the kagome lattice.Self-assembly and kinetic mechanism of complex colloidal cluster crystals based on soft one-patch particles:As a typical complex three-dimensional crystal,the complex colloidal χ phase may enable potential applications in the fields of structural color palettes,hybrid materials,electronic paper display,and multifunctional materials due to the extremely complex structure.How to construct complex χ phase at the micro/nano scale by simple colloidal particles remains a challenge in materials science.We construct complex colloidal cluster χ phase by self-assembly of polymer soft one-patch(Janus)colloidal particles.The shape and dispersity of colloidal clusters can be controlled by tuning the patch size and interaction between particles.The colloidal clusters of different shapes and sizes will further pack to abundant cluster crystals including χphase.The formation of the colloidal cluster χ phase undergoes a remarkable two-step self-assembly process.The soft one-patch colloidal particles first self-assemble to form colloidal clusters with specific size dispersity,then these colloidal clusters further pack into colloidal cluster χ phase.The results of kinetics simulation show that the dynamic particle exchange between clusters is an important factor for stabilizing the complex colloidal cluster χ phase.Cooperative self-assembly mechanism of colloidal cubic diamond photonic crystals based on two-patch particles:Colloidal cubic diamond crystals with lowcoordinated and staggered structure could exhibit a wide photonic band gap at low refractive index contrast,which makes it extremely valuable for photonic applications.However,self-assembly of cubic diamond crystal using simple colloidal building blocks is still considerably challenging,due to its low packing fraction.The cubic diamond structure is obtained by utilizing cooperative self-assembly of polymer-based two-patch(triblock Janus)colloidal particles and isotropic colloidal spheres to form a superlattice.The pyrochlore structure assembled by two-patch particles acts as a soft template to direct the packing of colloidal spheres into cubic diamond lattice.Numerical simulations show that this cooperative self-assembly strategy works well in a large range of particles size ratios of these two species.A class of highly-ordered crystal lattices,especially the desired cubic diamond lattice,can be obtained via directed packing of isotropic colloidal spheres by properly tuning the particle size ratio and interaction strength between two species of colloidal particles.The calculation of the photonic structure shows that the obtained cubic diamond crystals exhibit wide and complete photonic bandgaps,the frequency and width of which can be easily adjusted by tuning the size ratio.