Core-shell droplets and microcapsules formed through liquid-liquid phase separation of a colloid-polymer mixture

TL;DR

This paper introduces a novel method for creating core-shell microcapsules using liquid-liquid phase separation of a colloid-polymer mixture, enabling stimuli-responsive encapsulation with aqueous components.

Contribution

The study demonstrates a new fabrication technique for core-shell microcapsules utilizing temperature-sensitive microgel particles and phase separation, suitable for biological and responsive applications.

Findings

Formed core-shell structures with stimuli-sensitive microgel shells.

Achieved encapsulation in aqueous environment with controllable properties.

Demonstrated potential for temperature, salt, or pH responsive capsules.

Abstract

Microcapsules allow for the controlled containment, transport, and release of cargoes ranging from pharmaceuticals to fragrances. Given the interest from a variety of industries in microcapsules and other core-shell structures, a multitude of fabrication strategies exist. Here, we report on a method relying on a mixture of temperature-responsive microgel particles, poly(N-isopropylacrylamide) (pNIPAM), and a polymer which undergo fluid-fluid phase separation. At room temperature this mixture separates into colloid-rich (liquid) and colloid-poor (gas) fluids. By heating the sample above a critical temperature where the microgel particles shrink dramatically and develop a more deeply attractive interparticle potential, the droplets of the colloid-rich phase become gel-like. As the temperature is lowered back to room temperature, these droplets of gelled colloidal particles reliquefy and phase separation within the droplet occurs. This phase separation leads to colloid-poor droplets within the colloid-rich droplets surrounded by a continuous colloid-poor phase. The gas/liquid/gas all-aqueous double emulsion lasts only a few minutes before a majority of the inner droplets escape. However, the colloid-rich shell of the core-shell droplets can solidify with the addition of salt. That this method creates a core-shell structures with a shell composed of stimuli-sensitive microgel colloidal particles using only aqueous components makes it attractive for encapsulating biological materials and making capsules that respond to changes in, for example, temperature, salt concentration, or pH.