| Cellulose nanocrystals(CNC)are widely used in the fields of nanofillers,biomedicine and water treatment due to their excellent reproducibility,biodegradability,mechanical strength and unique liquid crystal behavior.Among them,the most striking is the use of CNC's unique chiral liquid crystal assembly behavior to prepare colored films and composite films with chiral nematic structure.So far,most of the research on the behavior of liquid crystals around CNC has focused on the rod-shaped CNC.In recent years,people have successfully prepared spherical CNCs,namely cellulose nanospheres(CNS).Regarding this new morphology of nanocrystals,whether it can also exhibit spontaneous liquid crystal assembly behavior,the influence of crystal morphology on the assembly of cellulose nanocrystalline liquid crystals needs to be clarified urgently.In view of this,this topic first prepared CNS,and conducted detailed research on the assembly behavior of CNS in aqueous dispersion and solid film after water volatilization.Then,rod-shaped CNCs with different aspect ratios were prepared,and the crystal morphology was discussed.Influence of the assembly behavior of cellulose nanocrystalline liquid crystals.The main research contents are as follows:1.Using pulp cellulose as the raw material,the pulp was pretreated first.The CNS and short rod-shaped CNC were prepared by the ultrasonic-assisted sulfuric acid hydrolysis method,and the long rod-shaped CNC was prepared by the sulfuric acid acid hydrolysis method.The diameter of CNS was in the range of 20-100 nm.The length of the short rod-shaped CNC is 70-120 nm,and the aspect ratio is 4-18,and the length of the long rod-shaped CNC is 180-400 nm,and the aspect ratio is 10-40.The three cellulose nanocrystals are all cellulose I crystal form,with crystallinity higher than 85%.The thermal stability of CNS is slightly better than that of the two rod-shaped CNCs.2.The liquid-phase assembly behaviors of spherical and rod-shaped CNCs were investigated,and the study showed that the phase behaviors of the three types of CNCs are all concentration-dependent.With the generation,growth and orientation of crystallike crystals,the suspension of cellulose nanocrystals has undergone a transition from an isotropic phase to a chiral nematic liquid crystal phase.Compared with rod-shaped CNC,CNS requires a longer time for liquid crystal assembly.During the phase change process,due to the small aspect ratio of CNS and narrow particle size distribution,no phase separation occurs,which is significantly different from rod-shaped CNC.After the liquid crystal structure is formed,the order and stability of the structure are low,and a high concentration can produce a special crisscross texture.3.The effect of crystal morphology on the film structure of cellulose nanocrystals after water volatilization was investigated,and the study showed that all three types of CNC morphology can obtain colored films after natural casting.Compared with the rodshaped CNC color film,the formation mechanism of the nanosphere color film is still unknown,but it is related to the periodic layered structure produced.A higher concentration of CNS suspension will produce structural color after volatilization to form a film to obtain a colored film,which is blue when viewed perpendicular to the film plane.The section of the CNS film shows that the film is composed of parallel periodic layered structures.Compared with the rod-shaped CNC color film,the color wavelength of the color film under the same casting film condition is shorter,and the internal layer period interval is smaller.In addition,the subject finally investigated the color change of the CNS color film during the wetting process.The study showed that with the infiltration of water molecules,the film color will change in the order of blue,green,yellow,orange,and red due to the increase of the interlayer spacing.The application of nanosphere colored film as a humidity response material provides theoretical guidance. |
PDF Full Text Request