Enhanced Ordering of Liquid Crystalline Suspensions of Cellulose Microfibrils: A Small Angle Neutron Scattering Study

Abstract

Small angle neutron scattering, SANS, was used to characterize the enhanced ordering induced by magnetic and shear alignment of chiral nematic liquid crystals of cellulose microfibrils in aqueous suspension. In a ∼2 T magnetic field the chiral nematic phase exhibits a uniform orientation over an entire 10 mL sample. SANS data confirmed that the cholesteric axis of this phase aligns along the magnetic field with implications that the distance between microfibrils is shorter along the cholesteric axis than perpendicular to it. This is consistent with the hypothesis that cellulose microfibrils are helically twisted rods. Under shear flow, the alignment of microfibrils changes from chiral nematic to nematic with relative order increasing with increasing shear rate. The axial ratio (length/width) is the key parameter in determining the relative order achieved and in determining the relaxation behavior after shear ceases.