posted on 2022-10-18, 12:36authored byVincenzo Calabrese, Csilla György, Simon J. Haward, Thomas J. Neal, Steven P. Armes, Amy Q. Shen
We investigate the
shear and extensional flow behavior of dispersions
composed of two types of worm-like nanoparticles (WLNPs) with comparable
cross-sectional diameters, similar persistence lengths but differing
contour lengths, and thus differing flexibility. By measuring the
flow-induced birefringence (FIB) of WLNP dispersions in two contrasting
microfluidic devices, we obtain an experimental quantification of
the role of shearing and planar extensional flows at aligning a short
and stiff WLNP (S-WLNP) and a relatively long and flexible WLNP (L-WLNP).
We show that shear and extensional flows induce the alignment of both
types of WLNPs. However, extensional deformations are more effective
than shear deformations at triggering the onset of alignment of the
WLNP. The difference between shear and extensional deformations for
WLNP alignment is explained based on the ratio of extensional and
shear viscosity of the solvent fluid (Trouton ratio of the solvent)
and a structural parameter related to the WLNP extensibility and flexibility.
Under shear flow, these WLNP dispersions display shear-thinning behavior,
with an exponential reduction in viscosity with increasing alignment.
Under extensional flow, the WLNP alignment leads to extensional thinning,
making WLNP ideal additives for industrial and biotechnology formulations
exposed to extensional dominated flows (e.g., jetting, spraying, and
printing processes).