Liquid pearls

TL;DR

This paper demonstrates a method to create liquid core capsules with a thin hydrogel membrane, using surfactant-induced transient rigidity to prevent mixing and enable encapsulation of various liquids.

Contribution

It introduces a novel technique employing surfactant precipitation to stabilize the interface during capsule formation, allowing for versatile liquid encapsulation.

Findings

Superimposing surfactant precipitation confers transient rigidity to the interface.

The method prevents mixing until gelling occurs, enabling creation of stable liquid pearls.

Capsules can contain almost any type of liquid.

Abstract

This fluid dynamics video reports how to form liquid core capsules having a thin hydrogel elastic membrane named liquid pearls. These fish-egg like structures are initially made of a millimetric liquid drop, aqueous or not, coated with an aqueous liquid film containing sodium alginate that gels once the double drop enters a calcium chloride bath. The creation of such pearls with micrometer thick membrane requires to suppress mixing until gelling takes place. Here, we show that superimposing a two dimensional surfactant precipitation at the interface confers a transient rigidity that can damp the shear induced instability at impact. Based on this, pearls containing almost any type of liquids can be created. The video focuses on the dynamics of the entry of the compound drop into the gelling bath.