| Sulfuric acid hydrolysis is the main method for preparing cellulose nanocrystals(CNC).However,its application in more fields is limited by some shortcomings such as poor heat resistance caused by sulfonate on the surface.Therefore,surface functionalization of cellulose nanocrystals is usually achieved by modification to expand its application range.Ionic liquids(IL)are a class of room temperature molten salts with excellent thermal stability,flame retardancy and high ionic conductivity,which are widely used in the fields of biocatalysis,electrochemical devices,engineering fluids and so on.We previously grafted ionic liquid onto CNC surface through covalent bond and successfully prepared CNC-IL.We found that the effective size of CNC-IL in the suspension was much larger than that of CNC,and it dispersed stably at a high positive potential,which would affect the liquid crystal selfassembly of CNC-IL.Studying the liquid crystal assembly behavior of CNC with positively charged ionic liquid grafted on its surface is helpful to explore the origin of the chiral nematic arrangement of cellulose nanocrystals.It lays a certain foundation for studying the self-assembly behavior of cellulose nanocrystals.Meanwhile,the self-assembly performance of CNC-IL has great application potential in the construction of high-performance and multifunctional materials.Therefore,we investigated the effect of grafting positively charged ionic liquid(IL)[VBIM][BF4] on the behavior of CNC chiral nematic liquid crystals.The results show that when the concentration of CNC-IL suspension varies between 0.05-4wt%,CNC-IL can observe finger texture at a lower concentration(1 wt%),and CNCIL forms chiral nematic liquid crystal.Different from CNC-OO3,the suspension is not divided into isotropic phase and liquid crystal phase,but the liquid crystal phase is dispersed in the suspension.With the increase of concentration,the volume of liquid crystal phase increases,and the pitch of chiral nematic liquid crystal formed decreases with the increase of the concentration of CNC-IL.Our analysis confirmed that the unique liquid crystal behavior of CNC-IL was due to the fact that the surface grafted ionic liquid was easy to combine with water to form a hydration layer,leading to the increase of the effective size of CNC-IL,and it was easier to contact and form a crosslinking network,leading to the high viscosity of the suspension,which restricted the movement of nanocellulose rods.Finally,we examined the bonding properties of CNC-IL and found that CNC-IL can form a labyrinth-like liquid crystal topology between the glass interface,and has a strong bond strength to the glass in the plane.When the concentration of 4wt% suspension is used as a binder,it can achieve a maximum load of more than 200 N.The liquid crystal self-assembly process induced by solvent vaporization at the glass interface was studied in situ with a polarizing microscope,and the formation mechanism of the strong bonding effect of CNC-IL was discussed. |
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