Illuminating the Impact of Solvent and Particle Properties on Optical Manipulation of Colloidal Nanomaterials

The precise control over the placement of colloidal nanomaterials has led to enticing emergent phenomena including transport through superlattices, strong coupling with optical cavities for quantum applications, and hybridization when different colloidal materials are interfaced. These applications and many more require precise spatial placement of nanoparticles as well as precise control over orientation. As an example, defects in wide-band gap nanomaterials or spins in semiconductor nanomaterials offer promising solutions for quantum technologies that are inaccessible to bulk materials, if the colloidal materials can be precisely positioned in an optical cavity. This requires a tool that acts on a single colloid in three dimensions, controls the angle of the colloid, and is applicable to a variety of particles and a variety of solvents. Optical manipulation methods such as optical trapping provide a unique platform that addresses these criteria, by trapping a particle in three dimensions and allowing for orientation control through polarization. However, we have limited understanding of how optical manipulation may change in the environments necessary for colloidal nanomaterials – <i>i.e. </i>organic solvents, ligands, or high refractive index materials. Here, we investigate the impact of particle composition, geometry, and size as well as solvent identity on optical trapping forces using a combination of experiments and multiphysics simulations. We investigate the impact of key variables such as viscosity and refractive index on optical trapping strength. Combining these results, we identify key relationships between solvent and colloidal nanomaterials to manipulate and orient nanomaterials and suggest guidelines to further improve optical manipulation.