Confined Crystallization in the Self-Assembled Nanostructures of Cellulose Nanocrystals and Polyethylene Glycol

Thin layers of semicrystallized polymers covered on nanoparticles significantly influence the multiple properties of their nanocomposites because of the confined crystallization of polymers. Cellulose nanocrystal (CNC) nanorods have a hydroxy-rich surface that favors the hydrogen-bonding interaction with polymers and a twisted nanostructure, which can construct a chiral nematic liquid-crystal phase scaffold for the filling of polymers. All these make CNCs' self-assembled nanostructure a unique confined condition for polymers. Understanding the crystallization of polymers in the coassembled CNC/polymer composites presents a challenge in this regard. In this study, we focus on the confinement crystallization in the coassembled composites of CNCs and poly(ethylene glycol)(PEG). The composition-dependent changes in composite morphology and crystallization have been extensively characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, synchrotronic powder X-ray diffraction, synchrotronic grazing incidence wide-angle X-ray diffraction, and differential scanning calorimetry. At low PEG content (10 wt.%), strong confinement has been identified, showing an extremely low crystallinity with tiny PEG crystallites. As the PEG reached 30 wt.%, the PEG (120) plane with the flat-on orientation of the crystal lamella appeared. As the PEG content increased continuously (40 wt.% to 50 wt.%), the intensity of the (120) plane of the PEG crystal became larger, accompanied by an increasing flat-on orientation degree. When the PEG weight percentage was up to 60 wt.%, the crystals grew randomly, losing their preferential orientation. The free growth of PEG crystals also induced a significantly decreased orientation degree of CNCs. The CNC/PEG system presents a mutual influence from two components, which enriches our understanding of the coassembly and confined crystallization of polymer composites. It will benefit the further modulation of CNC-based nanocomposites, both in their structures and properties.