title: Hygroscopic Swelling Determination of Cellulose Nanocrystal (CNC) Films by Polarized Light Microscopy Digital Image Correlation.
abstract: The coefficient of hygroscopic swelling (CHS) of self-organized and shear-oriented cellulose nanocrystal (CNC) films was determined by capturing hygroscopic strains produced as result of isothermal water vapor intake in equilibrium. Contrast enhanced microscopy digital image correlation enabled the characterization of dimensional changes induced by the hygroscopic swelling of the films. The distinct microstructure and birefringence of CNC films served in exploring the in-plane hygroscopic swelling at relative humidity values ranging from 0% to 97%. Water vapor intake in CNC films was measured using dynamic vapor sorption (DVS) at constant temperature. The obtained experimental moisture sorption and kinetic profiles were analyzed by fitting with Guggenheim, Anderson, and deBoer (GAB) and Parallel Exponential Kinetics (PEK) models, respectively. Self-organized CNC films showed isotropic swelling, CHS ∼0.040 %strain/%C. By contrast, shear-oriented CNC films exhibited an anisotropic swelling, resulting in CHS ∼0.02 and ∼0.30 %strain/%C, parallel and perpendicular to CNC alignment, respectively. Finite element analysis (FEA) further predicted moisture diffusion as the predominant mechanism for swelling of CNC films.
authors.affiliation: School of Materials Engineering, Purdue University , 701 West Stadium Avenue, West Lafayette, Indiana 47907, Unites States.
authors.forename: Shikha
authors.identifier: http://orcid.org/0000-0002-0774-3144
authors.initials: S
authors.lastname: Shrestha
authors.affiliation: School of Materials Engineering, Purdue University , 701 West Stadium Avenue, West Lafayette, Indiana 47907, Unites States.
authors.forename: Jairo A
authors.initials: JA
authors.lastname: Diaz
authors.affiliation: School of Materials Engineering, Purdue University , 701 West Stadium Avenue, West Lafayette, Indiana 47907, Unites States.
authors.forename: Siavash
authors.initials: S
authors.lastname: Ghanbari
authors.affiliation: School of Materials Engineering, Purdue University , 701 West Stadium Avenue, West Lafayette, Indiana 47907, Unites States.
authors.forename: Jeffrey P
authors.initials: JP
authors.lastname: Youngblood
mesh_terms: D016880:Anisotropy; D002482:Cellulose / Q000737:chemistry*; D008859:Microscopy, Polarization; D008956:Models, Chemical; D053758:Nanoparticles / Q000737:chemistry*; D017155:Wettability
chemical_list: D002482:Cellulose; C109691:microcrystalline cellulose