Cooperative Ordering and Kinetics of Cellulose Nanocrystal Alignment in a Magnetic Field
De France, K.J.; Yager, K.G.; Hoare, T.; Cranston, E.D. "Cooperative Ordering and Kinetics of Cellulose Nanocrystal Alignment in a Magnetic Field" Langmuir 2016
We study the assembly of cellulose nano-crystals when in the presence of a magnetic field. Using in-situ small-angle x-ray scattering measurements (during magnetic field alignment), we show evidence of cooperative ordering of the nanocrystals.
Cellulose nanocrystals (CNCs) are emerging nanomaterials that form chiral nematic liquid crystals above a critical concentration (C*) and additionally orient within electromagnetic fields. The control over CNC alignment is significant for materials processing and end use; to date, magnetic alignment has been demonstrated using only strong fields over extended or arbitrary time scales. This work investigates the effects of comparatively weak magnetic fields (0–1.2 T) and CNC concentration (1.65–8.25 wt %) on the kinetics and degree of CNC ordering using small-angle X-ray scattering. Interparticle spacing, correlation length, and orientation order parameters (eta and S) increased with time and field strength following a sigmoidal profile. In a 1.2 T magnetic field for CNC suspensions above C*, partial alignment occurred in under 2 min followed by slower cooperative ordering to achieve nearly perfect alignment in under 200 min (S = -0.499 where S = -0.5 indicates perfect antialignment). At 0.56 T, nearly perfect alignment was also achieved, yet the ordering was 36% slower. Outside of a magnetic field, the order parameter plateaued at 52% alignment (S = -0.26) after 5 h, showcasing the drastic effects of relatively weak magnetic fields on CNC alignment. For suspensions below C*, no magnetic alignment was detected.