Mapping Anisotropic and Heterogeneous Colloidal Interactions via Optical Laser Tweezers

Heterogeneity
among particles is an inherent feature that allows
nondeterministic prediction of the properties of assembled structures
and materials composed of many particles. Here, we report a promising
strategy to quantify the heterogeneous and anisotropic interactions
between ellipsoid particles using optical laser tweezers. The configuration
and separation between two particles at an oil–water interface
were optically controlled, and the capillary interaction behaviors
were directly observed and measured. As a result, the optimal particle
configurations at energetically favorable states were obtained, and
the interaction forces between the particles were identified accurately
by determining the trap stiffness in the direction of major and minor
axes of the particle. Visualization of the capillary field around
individual particles confirmed that the capillary interactions were
quadrupolar, anisotropic, and heterogeneous. The measurement method
presented here can be widely used to quantify interaction fields for
various types of anisotropic particles.