D. Bartolo | Searcharxiv

arXiv2011

Geometric scaling of purely-elastic flow instabilities

We present a combined experimental, numerical and theoretical investigation of the geometric scaling of the onset of a purely-elastic flow instability in a serpentine channel. Good qualitative agreement is obtained between experiments, using dilute solutions of flexible polymers in microfluidic devices, and two-dimensional numerical simulations using the UCM model. The results are confirmed by a simple theoretical analysis, based on the dimensionless criterion proposed by Pakdel-McKinley for onset of a purely-elastic instability.

cond-mat.soft↗

arXiv1999

Long-range Casimir interactions between impurities in nematic liquid crystals and the collapse of polymer chains in such solvents

The elastic interactions between objects embedded in a nematic liquid crystal are usually caused by the average distorsion-rather than by the fluctuations-of the nematic orientational field. We argue that for sufficiently small particles, the nematic-mediated interaction originates purely from the fluctuations of the nematic director. This Casimir interaction decays as d^(-6), d being the distance between the particles, and it dominates van der Waals interactions close to the isotropic-to-nematic transition. Considering the nematic as a polymer solvent, we show that the onset of this Casimir interaction at the isotropic-to-nematic transition can discontinuously induce the collapse of a flexible polymer chain from the swollen state to the globular state, without crossing the Theta-point.

cond-mat.soft↗