Liquid Crystalline Behavior Of Cellulose Nanocrystals In Compatible Biphasic System

The broad utility of cellulose nanocrystals(CNCs)as an environmentally-friendly and colorful coating is limited by the instability of their coloration,rigidity and brittleness.CNCs have shown great potentials in colorful coating applications due to its unique inherent ability to self-assemble and specific optical properties.Tuning the coloration by modifying the structure of the chiral nematic organization and improving the interface compatibility of CNCs with substrates is essential for developing optical coating materials.In the thesis,CNCs suspension was prepared by acid hydrolysis of cellulose.Two cellulose derivatives,hydroxypropyl cellulose(HPC)and carboxymethyl cellulose(CMC);four polyhydric alcohols with low molecular weight,maltitol,poly(ethylene glycol)400(PEG400),sorbitol and pentaerythritol,and a neutral polymer,poly(ethylene glycol)20000(PEG20000)were introduced into CNCs coating films through evaporation-induced self-assembly(EISA).The mesophase transition,structure-color and mechanical properties of the coatingsand coating films were characterized by UV-vis spectroscopy,polarized light microscopy(PLM),scanning electron microscopy(SEM),wide-angle X-ray diffraction(WXRD),rheological and tensile tests.Also,the adhesion between CNC/PEG20000 coatings and different polymer matrices were tested.The results indicate that the cholesteric phase of CNCs was preserved with the addition of HPC to the CNCs matrix,whereas adding CMC to CNCs prevented the formation of cholesteric phase thus resulting in poor optical properties in the composite films produced.Also the addition of moltitol,PEG400 and sorbitol took effect as perfect color-tuner by positively impacting the structure-color of the CNCs coating films via the production of a red-shift in the visible spectrum with a well-pronounced fingerprint texture.Again,the reflective wavelength of the iridescent CNCs was finely tuned by incorporation of PEG20000 with varied loadings from 2.5 to 50 wt%,although high loading contents of PEG20000 did produce some side effects due to severe microphase separation.Moreover,PEG20000 played an effective plasticizer to improve the ductility or flexibility of the CNC coating and coating film.Furthermore,as a compatibilizer,PEG20000 could effectively and tremendously enhance theadhesion strength between CNCs and neutral polymer matrices without destroying the chiral nematic mesophases of CNCs.It is anticipated that these environmentally friendly CNC/PEG composites with excellent tunable iridescence,good flexibility,and high bonding strength tohydrophobic polymer matrices could be promising candidates in modern green paint industry and related technologies.