Interfacial Assembly of Dye-Doped Microparticles Driven by Combined Optical and Non-Optical Forces

Optical trapping has emerged as an alternative method for controlling the assembly of nano- and microparticles at the microscale. This process involves optical, electrostatic, capillary, and hydrodynamic forces. Additionally, absorption forces also come into play for particles containing chromophores. This work proposes and experimentally demonstrates a model for photoexcitation-mediated particle assembling using single particle tracking analysis. The dispersed dye-doped microparticles are pushed toward the air/solution interface by absorption force, leading to their association and formation of hexagonal-close-packed (HCP) assemblies. These observations indicate that the assembly is facilitated by coupling the absorption force with other non-optical forces. The results presented show the potential of using absorption forces to control and modify the structural order of particles, for optical assemblies as well as for general self-assembly of various materials (e.g., polymers, proteins) at an interface.