Study Of Epitaxial Crystallization On Uniaxial Thin Films Composed Of Cellulose Nanocrystals

Cellulose Nanocrystals(CNCs)is an important kind of one-dimension(1D)nanoparticles,we designed a dip-coating method to fabricate uniaxial CNC thin films from its colloidal suspension.Subsequently,these thin films successfully guided the epitaxial crystallization of small organic molecules and semicrystalline polymers(SCPs).For small organic molecules,taking indomethacin(INN)as an example,at first its liquid precursors were spin-coated on a uniaxial CNC thin film.Subsequently ethanol vapor was used to promote its crystallization and finally highly oriented INN crystal arrays were obtained.We analyzed the 3D orientation of INN crystals by multiple characterization tools and studied the crystallization mechanisms using molecular dynamics simulation.For semi-crystalline polymers,a 3D orientational thin film of poly(?-caprolactone)(PCL)was epitaxially crystallized onto a uniaxial CNC substrate.Multiple characterization methods,including X-ray diffraction,scattering,and various microscopic imaging technique,were employed to study the crystal structures and orientations of the PCL thin films systematically.A distinct orientational relation was found between the PCL overlayer and the underneath uniaxial CNC templates.Furthermore,the CNCs underneath functioning as heterogeneous nuclei significantly improves the crystallization kinetics of PCL overlayer.Notably,our assembly route is based on the aqueous suspension of 1D nanoparticles to fabricate uniaxial thin films as substrates using a low-cost dip-coating method.This route is environmentally benign and highly efficient,and feasible to achieve high-throughput and continuous manufacturing,which imparts it a high potential value in industrial application.We have also thoroughly investigated the influences of the uniaxial CNC substrate on the crystal orientations and organizations of the epitaxial small organic molecules and semicrystalline polymers,as well as the crystallization kinetics.Moreover,we achieved orientational CNC assembly and subsequent epitaxial crystallization on nonplanar substrates,widening the applications of oriented crystalline materials in integration of flexible functional devices.