title: Cooperative Ordering and Kinetics of Cellulose Nanocrystal Alignment in a Magnetic Field.
abstract: 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 (η 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.
authors.affiliation: Department of Chemical Engineering, McMaster University , 1280 Main Street West, Hamilton, ON L8S 4L8, Canada.
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: De France
authors.affiliation: Center for Functional Nanomaterials, Brookhaven National Laboratory , Upton, New York 11973, United States.
authors.forename: Kevin G
authors.initials: KG
authors.lastname: Yager
authors.affiliation: Department of Chemical Engineering, McMaster University , 1280 Main Street West, Hamilton, ON L8S 4L8, Canada.
authors.forename: Todd
authors.initials: T
authors.lastname: Hoare
authors.affiliation: Department of Chemical Engineering, McMaster University , 1280 Main Street West, Hamilton, ON L8S 4L8, Canada.
authors.forename: Emily D
authors.initials: ED
authors.lastname: Cranston