Viscoelastic liquid bridge breakup and liquid transfer between two surfaces

We studied experimentally the breakup of liquid bridges made of aqueous solutions of Poly(acrylic acid) between two separating solid surfaces with freely moving contact lines. For polymer concentrations higher than a certain threshold (-30 ppm), the contact line on the surface with the highest receding con-tact angle fully retracts before the liquid bridge capillary breakup takes place at its neck. This means that all the liquid remains attached to the opposing surface when the surfaces are separated. This behavior occurs regardless of the range of liquid volume and stretching speed studied. Such behavior is very different from that observed for Newtonian liquids or non-Newtonian systems where contact lines are intentionally pinned. It is shown that this behavior stems from the competition between thinning of bridge neck (delayed by extensional thickening) and receding of contact line (enhanced by shear thinning) on the surface with lower receding contact angle. If the two surfaces exhibit the same wetting properties, the upper contact line fully retracts before the capillary breakup due to the asymmetry caused by gravity, and, therefore, all the liquid remains on the lower surface. (C) 2020 Published by Elsevier Inc.

Automated summary

Experimental study on the breakup of liquid bridges composed of aqueous Poly(acrylic acid) solutions reveals that for polymer concentrations exceeding a threshold, the contact line on the surface with the highest receding contact angle fully retracts before the liquid bridge capillary breakup occurs, causing the liquid to remain on the opposing surface. This behavior is attributed to the competition between thinning of the bridge neck and receding of the contact line on the surface with lower receding contact angle.