# Colloidal self-assembly at an interface

Edited by Qichao Hu

September 19th, 2010

reference: [1]

It is well known that colloidal particles can form at the interfaces between liquids. This phenomenon can be used to self-assemble colloidal particles and ultimately to synthesize new materials.

The colloidal particles' ability to bind to liquid and stabilize emulsion is guided by the need to minimize interfacial energy. When a particle moves from a liquid to a liquid-liquid interface, the change in free energy is

$\Delta G=-\pi R^2\gamma_{OW} (1-\cos\theta_C)^2$

where $R$ is the particle radius, $\gamma_{OW}$ is the energy per unit area of the liquid-liquid interface, and $\theta_C$ is the contact angle. The contact angle is related to the energy per unit area of the various interfaces through: $\cos\theta_C=(\gamma_{PO}-\gamma_{PW})/\gamma_{OW}$, where $\gamma_{PO}$ is at the particle-oil interface, and $\gamma_{PW}$ is at the particle-water interface.

The paper focuses on how to control the assembly of colloidal particles at liquid-liquid interfaces. The control methods are divided into two categories:

1) controlling the geometry at the interface

2) controlling the particle-particle interaction at the interface