la6b03724_si_002.mpg (2.37 MB)
Influence of the Particle Concentration and Marangoni Flow on the Formation of Cellulose Nanocrystal Films
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posted on 2017-01-10, 00:00 authored by Alican Gençer, Christina Schütz, Wim ThielemansCellulose 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.