Single Molecular Layer of Chitin Sub-Nanometric Nanoribbons: One-Pot Self-Exfoliation and Crystalline Assembly into Robust, Sustainable, and Moldable Structural Materials.

Sub-nanometric materials (SNMs) represent a series of unprecedented size-/morphology-related properties applicable in theoretical research and diverse cutting-edge applications. However, in-depth investigation and wide utilization of organic SNMs are frequently hindered, owing to the complex synthesis procedures, insufficient colloidal stability, poor processability, and high cost. In this work, a low-cost, energy-efficient, convenient, effective, and scalable method is demonstrated for directly exfoliating chitin SNMs from their natural sources through a one-pot "tandem molecular intercalation" process. The resultant solution-like sample, which exhibits ribbon-like feature and contains more than 85% of the single molecular layer (thickness <0.6 nm), is capable of being solution-processed to different types of materials. Thanks to the sub-nanometric size and rich surface functional groups, chitin SNMs reveal versatile intriguing properties that rarely observe in their nano-counterparts (nanofibrils), e.g., crystallization-like assembly in the colloidal state and alcoplasticity/self-adhesiveness in the bulk aggregate state. The finding in this work not only opens a new avenue for the high value-added utilization of chitin, but also provides a new platform for both the theoretical study and practical applications of organic SNMs.

Fabrication of Oriented Colloidal Crystals from Capillary Assembly of Polymer-Tethered Gold Nanoparticles.

Self-assembled colloidal crystals (CCs) or nanoparticle (NPs) superlattices have attracted significant attention due to their potential applications in many fields. However, due to the complex interactions that govern the self-assembly, it is difficult to predict and control the superstructure organization of CCs. Herein, a facile yet effective way is demonstrated to fabricate oriented CCs from capillary assembly of polymer-tethered gold NPs (AuNPs). Assembly mechanism of polymer-tethered AuNPs and their superlattice structures are systematically studied by in situ small-angle X-ray scattering (SAXS) technology. The results show that the oriented CCs of polymer-tethered AuNPs can be obtained upon solvent evaporation in a capillary tube and the oriented structure is mainly determined by the chain length of polymer ligands and size of AuNPs. Assembly of AuNPs tethered by short-chain ligand can result in oriented face-centered cubic (fcc) superlattice, whereas AuNPs tethered by long-chain ligand can assemble into an oriented body-centered tetragonal (bct) superlattice structure. Interestingly, in situ SAXS study shows that for the sample of bct superlattice structure, a transformation from fcc to bct superlattice upon solvent evaporation is observed, which strongly depends on chain length of ligands. This work provides a useful guide for polymer-tethered AuNPs to prepare orientation colloidal crystals.

Pseudosolvent Intercalator of Chitin: Self-Exfoliating into Sub-1 nm Thick Nanofibrils for Multifunctional Chitinous Materials.

Traditionally, energy-intensive and time-consuming postmechanical disintegration processes are inevitable in extracting biopolymer nanofibrils from natural materials and thereby hinder their practical applications. Herein, a new, convenient, scalable, and energy-efficient method for exfoliating nanofibrils (ChNFs) from various chitin sources via pseudosolvent-assisted intercalation process is proposed. These self-exfoliated ChNFs possess controllable thickness from 2.2 to 0.8 nm, average diameter of 4-5 nm, high aspect ratio up to 103 and customized surface chemistries. Particularly, compared with elementary nanofibrils, ChNFs with few molecular layers thick exhibit greater potential to construct high-performance structural materials, e.g., ductile nanopapers with large elongation up to 70.1% and toughness as high as 30.2 MJ m-3 , as well as soft hydrogels with typical nonlinear elasticity mimicking that of human-skin. The proposed self-exfoliation concept with unique advantages in the combination of high yield, energy efficiency, scalable productivity, less equipment requirements, and mild conditions opens up a door to extract biopolymer nanofibrils on an industrial scale. Moreover, the present modular ChNFs exfoliation will facilitate researchers to study the effect of thickness on the properties of nanofibrils and provide more insight into the structure-function relationship of biopolymer-based materials.