Preparation And Properties Of Cellulose Chiral Nematic Liquid Crystals

Cellulose is one of the most abundant renewable natural polymers in the world, soit has been paid much attention and widely investigated by the chemists. In this thesis,lyotropic chiral nematic liquid crystals (N*-LCs) were prepared from styela clava andcotton cellulose, and their structure and optical properties of the dried film from theN*-LCs were studied. And also the nanocomposites of polyaniline (PANI) andcellulose nanocrystals (CNs) were studied.Ascidian, a kind of tunicate, which can secrete cellulose, is the second largestsource of cellulose. Because ascidian cellulose with high crystallinity consists ofnearly pure (90%) Iβphase, it has been extensively studied in recent years. In thisthesis, styela clava, a kind of ascidian, was used as raw material to extract cellulose bysoaking in alkali solution and bleaching, and prepare the N*-LCs by acid hydrolysis.The N*-LCs and nanocomposites of PANI and the CNs were characterized by Fouriertransform infrared spectroscopy (FT-IR), polarizing microscopy (POM), scanningelectron microscopy (SEM), and atomic force microscopy (AFM). It was found thatbirefringence of styela clava cellulose suspension was concerned with theconcentration. POM observation revealed that N*-LCs could form and the pitch of theN*-LCs was about20μm when the concentration of suspension of styela clavacellulose achieved by acid hydrolysis for15hours was5wt%. For styela clavacellulose, longer hydrolysis time led to shorter cellulose rods with narrower particlelength distribution, but the width and height didn’t change. With the same hydrolysisconditions, the size of styela clava cellulose was much larger than that of cottoncellulose. Compared with ascidian cellulose, plant cellulose with much more source caneasily form N*-LCs by acid hydrolysis. Cotton cellulose N*-LCs were prepared byacid hydrolysis. Then POM was used to research the influence of reaction time,concentration of the CNs suspension on the optical properties of the suspension, andthe effect of magnetic field on the N*-LCs. The morphology and size of CNs whichformed the N*-LCs were characterized using SEM and AFM. The results indicatedthat the cellulose N*-LCs didn’t form after acid hydrolysis for1hour, while theyformed after acid hydrolysis for3.5hours at the cellulose concentration of4wt%, andthe pitch was about15μm. The film cast from a drop of chiral nematic phasesuspension in an8T static field for12hours exhibited a monodomain fingerprinttexture. The rod-like CNs which formed chiral nematic phase were100-400nm inlength,30-70nm in width,6-10nm in height.The nanocomposites of PANI and CNs were synthesized by in-situpolymerization in the cotton CNs suspension. SEM and TEM images indicated that theweight ratio of CNs and aniline in the suspension significantly influenced theinteraction between CNs and PANI, and the size of the PANI particles. It was foundthat PANI/CNs nanocomposites were good semiconductor materials, and that theweight ratio of CNs and aniline in the suspension affected the conductivity ofcomposites using standard four-probe technique.