title: Influence of the Particle Concentration and Marangoni Flow on the Formation of Cellulose Nanocrystal Films.
abstract: Cellulose nanocrystals (CNCs), ribbonlike crystalline nanoparticles, are a biobased material that can be a great alternative to obtaining films with tunable optical properties. Iridescent and light-diffracting films can be readily obtained via the drying of a suspension of these cellulose nanocrystals. The characteristics of the particle deposition process together with the self-assembly in the precluding suspension has a direct effect on the optical properties of the obtained films. Particle deposition onto a substrate is affected by the flow dynamics inside sessile droplets and usually yields a ring-shaped deposition pattern commonly referred to as the coffee-ring effect. We set out to measure and describe the drying kinetics under different conditions. We found that the Marangoni flow inside the droplet was too small to counteract the capillary flow that deposits CNCs at the edges, resulting in the coffee-ring effect, irrespective of the atmospheric humidity. By varying the amount of ethanol in the atmosphere, we were able to find a balance between (1) colloidal stability in the droplet, which is reduced by ethanol diffusion into the droplet, and (2) increasing Marangoni flow relative to capillary flow inside the droplet by changing the droplet surface tension. We could thus make iridescent films with a uniform thickness.
authors.affiliation: Renewable Materials and Nanotechnology Research Group, Department of Chemical Engineering, KU Leuven, Campus Kulak Kortrijk , Etienne Sabbelaan 53, 8500 Kortrijk, Belgium.
authors.forename: Alican
authors.initials: A
authors.lastname: Gençer
authors.affiliation: Renewable Materials and Nanotechnology Research Group, Department of Chemical Engineering, KU Leuven, Campus Kulak Kortrijk , Etienne Sabbelaan 53, 8500 Kortrijk, Belgium.
authors.forename: Christina
authors.identifier: 0000-0003-0238-1639
authors.initials: C
authors.lastname: Schütz
authors.affiliation: Renewable Materials and Nanotechnology Research Group, Department of Chemical Engineering, KU Leuven, Campus Kulak Kortrijk , Etienne Sabbelaan 53, 8500 Kortrijk, Belgium.
authors.forename: Wim
authors.identifier: 0000-0003-4451-1964
authors.initials: W
authors.lastname: Thielemans
mesh_terms: D002482:Cellulose; D003890:Desiccation; D053758:Nanoparticles; D013500:Surface Tension; D013535:Suspensions
chemical_list: D013535:Suspensions; D002482:Cellulose