title: Thermal expansion of self-organized and shear-oriented cellulose nanocrystal films.
abstract: The coefficient of thermal expansion (CTE) of cellulose nanocrystal (CNC) films was characterized using novel experimental techniques complemented by molecular simulations. The characteristic birefringence exhibited by CNC films was utilized to calculate the in-plane CTE of self-organized and shear-oriented self-standing CNC films from room temperature to 100 °C using polarized light image correlation. CNC alignment was estimated via Hermans order parameter (S) from 2D X-ray diffraction measurements. We found that films with no preferential CNC orientation through the thickness (S: ∼ 0.0) exhibited an isotropic CTE (∼25 ppm/K). In contrast, films with aligned CNC orientations (S: ∼0.4 to 0.8) had an anisotropic CTE response: For the highest CNC alignment (S: 0.8), the CTE parallel to CNC alignment was ∼9 ppm/K, while that perpendicular to CNC alignment was ∼158 ppm/K. CNC film thermal expansion was proposed to be due primarily to single crystal expansion and CNC-CNC interfacial motion. The relative contributions of inter- and intracrystal responses to heating were explored using molecular dynamics simulations.
authors.affiliation: School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907, United States. jdiazama@purdue.edu
authors.forename: Jairo A
authors.initials: JA
authors.lastname: Diaz
authors.forename: Xiawa
authors.initials: X
authors.lastname: Wu
authors.forename: Ashlie
authors.initials: A
authors.lastname: Martini
authors.forename: Jeffrey P
authors.initials: JP
authors.lastname: Youngblood
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Moon
mesh_terms: D016880:Anisotropy; D002236:Carbohydrate Conformation; D002482:Cellulose / Q000737:chemistry*; D008422:Materials Testing; D056004:Molecular Dynamics Simulation; D053758:Nanoparticles / Q000737:chemistry*; D013816:Thermodynamics; D014961:X-Ray Diffraction
chemical_list: D002482:Cellulose