# Polymer-Wrapped Oil Droplets and Polymer Particles with Complex Curvilinear Polyhedral Geometries by Surfactant-Driven Elastocapillary Buckling of Polymer Capsules

## TL;DR

Adding surfactants to polymer capsules changes their shape, enabling the creation of complex polymer particles with unique geometries.

## Contribution

A new method for creating complex polymer particles using surfactant-induced shape changes in deformable capsules.

## Key findings

- Surfactants induce complex shape changes in polymer capsules and oil droplets with multiple symmetries.
- Photopolymerization of deformed oil droplets produces anisotropic polymer particles.
- Degradable polymer cages allow isolation of cage-free complex-shaped particles.

## Abstract

Surfactants have been widely used to tune interfacial
tensions
in colloidal dispersions, resulting in phenomena such as wetting/dewetting,
emulsification, and foaming. In this study, we report that adding
micromolar concentrations of surfactants to aqueous dispersions of
thin, deformable polymer microcapsules partially filled with droplets
of oil induces complex shape changes in both the capsules and the
encapsulated oil droplets. Using video microscopy and confocal microscopy,
we observed the evolution of complex, anisotropic shapes with apparent
six-, five-, four- and 3-fold symmetries in the presence of added
surfactant and identified several factors influencing these shape
changes and the resulting distribution of shapes, including surfactant
concentration and charge, polymer capsule diameter and wall thickness,
and the size of the encapsulated oil droplets. Our results suggest
that these shape changes are driven by elastocapillarity, in which
the addition of surfactant changes the balance between elastic energy
and interfacial energy. Furthermore, we show that photopolymerization
of deformed droplets of vinyl monomer oils “caged” in
these capsules can be used to template the synthesis of polymer particles
with complex anisotropic shapes similar to those of the folded and
polymer-wrapped oil-filled capsules prior to polymerization. Finally,
we demonstrate that the use of degradable polymer cages enables the
isolation of “cage-free” polymer particles with complex
shapes and geometries.