Abstract :
[en] The cholesteric liquid crystal self-assembly of water-suspended cellulose nanocrystal
(CNC) into a helical arrangement was observed already more than 20 years ago, and
the phenomenon was used to produce iridescent solid films by evaporating the solvent
or via sol–gel processing. Yet, it remains challenging to produce optically uniform films
and to control the pitch reproducibly, reflecting the complexity of the three-stage drying
process that is followed in preparing the films. An equilibrium liquid crystal phase formation
stage is followed by a non-equilibrium kinetic arrest, which in turn is followed by
structural collapse as the remaining solvent is evaporated. Here, we focus on the first of
these stages, combining a set of systematic rheology and polarizing optics experiments
with computer simulations to establish a detailed phase diagram of aqueous CNC suspensions
with two different values of the surface charge, up to the concentration where
kinetic arrest sets in. We also study the effect of varying ionic strength of the solvent.
Within the cholesteric phase regime, we measure the equilibrium helical pitch as a function
of the same parameters. We report a hitherto unnoticed change in character of the
isotropic–cholesteric transition at increasing ionic strength, with a continuous weakening
of the first-order character up to the point where phase coexistence is difficult to detect
macroscopically due to substantial critical fluctuations.
FnR Project :
FNR8331546 - Materials Innovation With Self-ordered Nanocellulose: From Fundamental Physics Of Self-assembly To Realization Of Commercially Appealing Functional Films, 2014 (01/02/2015-31/01/2018) - Jan Peter Felix Lagerwall
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