Multiple droplets formation in ultrathin bridges of rigid rod dispersions

Abstract

In the present paper, we study the rheology of the dispersion of rigid rods in the course of capillary thinning of a liquid bridge formed during extension of a liquid droplet between two solid surfaces. Emergence of multiple annular microdroplets of solvent on the surface of the bridge is predicted. This process comes into play once the radius of the jet decreases below a critical value smaller than the rod length. Formation of the solvent annuli initially occurs by an activation mechanism, whereby the rods become trapped inside the jet core. The kinetics of the annular droplets growth in the regimes of both high and low activation barriers are considered in detail. Several kinetic regimes are studied, including activation, the linear regime when the annular droplets grow exponentially, and the consecutive nonlinear regime of significant core thinning and slow coalescence and growth of droplets. The phase-separation mechanism proposed here for dispersions of rigid rods in the ultrathin jet regime (when jet thickness a is much smaller than the rod length L) effectively replaces the classical Plateau–Rayleigh pinching; the proposed mechanism can, therefore, prevent the bridge from breaking in this regime, thereby opening up a new route for fiber formation in these systems.In the present paper, we study the rheology of the dispersion of rigid rods in the course of capillary thinning of a liquid bridge formed during extension of a liquid droplet between two solid surfaces. Emergence of multiple annular microdroplets of solvent on the surface of the bridge is predicted. This process comes into play once the radius of the jet decreases below a critical value smaller than the rod length. Formation of the solvent annuli initially occurs by an activation mechanism, whereby the rods become trapped inside the jet core. The kinetics of the annular droplets growth in the regimes of both high and low activation barriers are considered in detail. Several kinetic regimes are studied, including activation, the linear regime when the annular droplets grow exponentially, and the consecutive nonlinear regime of significant core thinning and slow coalescence and growth of droplets. The phase-separation mechanism proposed here for dispersions of rigid rods in the ultrathin jet regime (when je...