Cellulose Nanocrystals (CNCs) is an important kind of one-dimension (1D) nanoparticles, which exhibit excellent dispersibility in aqueous phase. In our group, a dip-coating method has been explored for fabrication of uniaxial thin coatings composed of densely-packed CNCs.
1. The uniaxial CNC thin coatings successfully guided the lateral crystallization of organic compounds and semicrystalline polymers, as the uniaxial alignment led to cellulose thin films with uniform crystallographic information for epitaxial growth. In the first case study, a sequential spin-coating and solvent fuming processes caused the formation of 3D-oriented crystal arrays of a typical pharmaceutical compound – indomethacin (INN). In another example, a continual spin-coating and annealing processes were employed for growing oriented thin films of a semicrystalline polymer. Multiple characterization tools, including X-ray diffraction, X-ray scattering, and optical and electron microscopic imaging techniques, were used for characterization of the structural information of final crystalline products. In both case studies, the uniaxial CNC thin coatings underneath function as heterogeneous nuclei for orientational guidance of the overlayers. We highlight this facile assembly approach to heterogeneous nuclei for the epitaxial crystallization and its extendability of achieving crystalline thin films on ambient substrates.
1. Nanowires with extreme aspect ratios are difficult to align. To date, processing methods based on shearing offer arguably the best access to aligning 1D nanoparticles into uniaxial thin coatings, accompanying drawbacks like proceeding with inclusion of inherently slow steps and complex processing techniques. Use the uniaxial alignment of V2O5·nH2O nanowires as an example. The uniaxial thin coatings composed of V2O5·nH2O nanowires were obtainable with a dip-coating method by using a binary stock dispersion containing CNCs with moderate aspect ratios. This approach can be readily extendable to the continuous production of thin coatings composed of uniaxial 1D nanoparticles on flexible substrates. Our findings could lead to integration of coating materials into flexible devices, where anisotropic properties is crucial for performance.