胶体纳米晶定向自组装构建Kagome晶格等复杂二维超晶格

momo

https://www.science.org/doi/10.1126/science.adu4125

简介
在胶体纳米晶自组装领域，如何构建结构复杂且热力学稳定的超晶格是长期挑战。传统研究多聚焦于球形、多面体等凸面纳米颗粒，但其对称性高、方向性相互作用调控受限，难以形成低对称性、低密度的非密堆积结构（如Kagome晶格）。本文突破性地引入非凸面哑铃形纳米晶（nanodumbbells,NDs），通过局部曲率匹配与耗尽作用（depletion interactions）的协同调控，实现了纳米晶的定向自组装，成功构建了Kagome晶格等复杂二维超晶格。这一研究不仅揭示了曲率在自组装中的关键作用，还为设计新型功能材料提供了新思路。
亮点
1.本工作实现了非凸面纳米哑铃的设计与可控合成。通过精准调控哑铃形纳米晶的腰部宽度（d/D比值），实现局部曲率的连续可调，赋予颗粒几何互补性。2.本工作证明了曲率引导的耗尽作用驱动长程有序组装。本工作引入游离油酸分子作为耗尽剂，增强颗粒间凹-凸区域的吸引力，克服非凸颗粒的位阻效应与动力学陷阱。耗尽作用与曲率匹配协同作用，使纳米哑铃在溶剂蒸发过程中逐步调整方向，形成热力学稳定的超晶格。3.本工作实现了Kagome晶格及其他复杂结构的成功构建。首次通过实验获得大面积、高有序的二维Kagome超晶格，并证实其热力学稳定性。通过调节纳米哑铃的曲率参数，可编程化组装平行、人字形、双人字形等多种超晶格，展现设计灵活性。

NANOMATERIALS

• This study explores the self-assembly behaviors of nonconvex, dumbbell-shaped nanocrystals (nanodumbbells) .
• It demonstrates the long-range ordered assembly into two-dimensional superlattices, including the chiral Kagome lattice, by tailoring the local curvature of nanodumbbells .
• Theoretical calculations confirm the Kagome lattice as a thermodynamically stable phase, with depletion interactions crucial for stabilizing these structures .
  

Synthesis and characterization of NDs

• Colloidal NaYF4:Yb/Er@NaGdF4@NaNdF4 nanocrystals were synthesized and coated with oleic acid ligands to ensure stability in nonpolar solvents .
• The waist width (d) of the nanodumbbells was tuned while keeping the length (L) and head width (D) relatively constant .
• The concavity of the nanodumbbells was defined using the waist-to-head width ratio (d/D), influencing their self-assembly behavior .
  

ND self-assembly and superlattice formation

• Concave-convex curvature fitting promoted specific bonding between NDs, with the bond directionality adjustable through local curvature modulation .
• Introducing depletion interactions by adding excess oleic acid mitigated kinetic arrest and promoted extended interlocking of NDs .
• 2D superlattices with varying structural complexities were assembled from NDs with different concavities, showing a common characteristic in their local packing .
  

Kagome lattices

• Moderate-concavity NDs were used to form Kagome lattices, known for their 2D arrangement of interconnected triangles, hexagons, and voids .
• The Kagome lattice displayed p6 symmetry, with each ND interlocking with its four nearest neighbors through hybrid fitting .
• The as-assembled Kagome lattice was a racemic mixture, comprising domains of both left and right handedness .
  

Formation mechanism

• Simulations indicated that purely hard-core interactions between NDs were insufficient to stabilize the Kagome lattice .
• Depletion interactions enhance attractive interactions between concave and convex regions of adjacent NDs, guiding them into arrangements needed to form the Kagome lattice .
• Calculations showed that NDs tended to adopt concave-convex fitting modes that maximize the overlapping exclusion volume (DVmax) .
  

Phase behavior

• A phenomenological parameter g was introduced to describe the relative strength of concave-convex interactions compared to other interactions .
• The phase diagram predicted that the Kagome lattice could form and coexist with the bi-chevron lattice when the d/D ratio ranged from ~0.55 to ~0.65, agreeing with experimental observations .
• The phase diagram also predicted stable phases for NDs with very narrow or wide waists, supported by experiments .
  

Binary superlattices and low-density superlattices

• Coassembling two types of NDs with differing dimensions led to the formation of AB3-type binary superlattices .
• Introducing multivalent bonding interactions through additional concave features led to the formation of an open oblique lattice .
• Multiple specific bonding interactions between neighboring NDs were likely responsible for stabilizing this unusual open lattice .
  

Conclusions

• The curvature of nonconvex NCs can be leveraged to program directional interparticle interactions .
• Curvature-guided depletion interactions facilitated global interlocking of NDs and stabilized open structures such as Kagome lattices .
• The curvature-mediated design principle could serve as a general strategy for guiding the self-assembly of various nonconvex NCs .