Building Superlattice In Soft Matter From Unimolecular Nanoparticles

Complex and ordered superlattices can be constructed by multistage self-assembly of soft materials.This"bottom-up"self-assembly technique has exhibited great potential.In science,the new concept of superlattice has attracted extensive attention and exploration in recent years.In engineering,the construction of nanoscale-ordered structures provides the basis for the development of metamaterials.However,precise regulation of self-assembled superlattices remains a challenge.Even when the primary molecules are precise,the supramolecular motifs（or secondary building blocks）can vary dramatically and become polydisperse,resulting in loss of accuracy.In soft matter,Giant molecules are a type of macromolecule with precise chemical structures,sequence,composition,topology and size.Based on giant molecules,we propose the concept of unimolecular nanoparticles（UMNPs）in the present work.The UMNPs act as the supramolecular motif and directly pack into the superlattices.The concept of UMNPs promotes the study of precise regulation of soft matter superlattice and their structural diversification.To seek the UMNPs in giant molecules,we designed and prepared a series of giant molecules with different chemical structures based on the“molecular LEGO”approach.The hierarchical self-assembled spherical superlattice of these giant molecules have been systematically studied,and a"giant molecules library"has been preliminarily established.Further,we studied the binary giant molecular superlattices and their evolution mechanism,as well as the binary blending superlattices from supramolecular motifs with different volumes asymmetry,such as Mg Zn₂（Laves C14）,Mg Cu₂（Laves C15）,etc.A Na Cl-type superlattice was obtained for the first time in condensed soft matter under a maximal volume asymmetry.In addition,to precisely design the binary superlattice from the molecular level,we developed a mathematical“single-shell”model of unary giant molecules.The“single-shell”model provides an understanding of soft matter superlattices from the supramolecular level,realizes precise prediction of the supramolecular motifs’radius,and guides the search for UMNPs.Based on our understanding of supramolecular motifs,we prepared a highly branched giant molecule,calledβCD-O₂₁.βCD-O₂₁is synthesized fromβ-cyclodextrin（βCD）as the core and 21 octyl-polyhedral polyhedral oligomeric silsesquioxanes（OPOSS）as ligands.We systematically explore its conformations and the superlattice ofβCD-O₂₁.βCD-O₂₁ can self-assemble into a highly ordered Frank-Kasper A15 superlattice in the bulk state by thermal annealing.The average motifs’radius is calculated to be 2.27 nm,and each motif contains oneβCD-O₂₁ molecule.Thus,a UMNP was obtained.Moreover,intriguing complex superlattices are discovered when blending this UMNP with other conventional giant molecules.These superlattices are Mg Zn₂,Mg Cu₂,Na Zn₁₃,and Al B₂,varied following the volume asymmetry.These binary mixtures provide direct evidence to support our previously proposed self-sorting process in the multicomponent co-assembly of soft matter.Based on the UMNPsβCD-O₂₁,we developed a series ofβ-cyclodextrin types of giant molecules,using cyclodextrin as the core and changing the chemical structures of OPOSS ligands.Most of theseβ-cyclodextrin types of giant molecules can construct spherical superlattices.5 types of UMNPs were found,whose radius could be adjusted from 2.2 to 2.8nm.We then binary mixed these UMNPs of different sizes ratio.The Frank-Kasperσphase was built at small volume asymmetry,while Mg Zn₂ superlattice was constructed at relatively large volume asymmetry.Particularly,the dynamics of UMNPs are further weakened by their rigidity and large size.During the thermal annealing process,a metastable quasicrystal structure was formed and then it transformed to stable Mg Zn₂ as time prolongs.The extension of UMNPs’size helped us to explore more complex blending systems of soft matter.At last,we have carried out a preliminary exploration of ternary giant molecular blends,based on the supramolecular motifs and UMNPs with varied sizes.With the increasing volume asymmetry,the ternary mixtures performed BCC,Mg Zn₂ superlattice,and a mixture of Mg Zn₂with Al B₂ superlattices at a large volume ratio.These binary superlattices（Mg Zn₂ or Al B₂）are composed of two components in the ternary blends.The third component can reduce the formation temperature of the superlattices and improve their degree of order.In general,the development of UMNPs enriches the types of"supramolecular motifs",improves the accuracy and diversity of superlattices,and lays a scientific foundation for the development of superlattice engineering and metamaterials.