Jinxin Fu 's Research Interest
Particle interactions determine the stability of nanoparticle suspensions and the phase separation of multiple particle mixtures. However, due to the small sizes of the dispersed particles and complexity of the physical and chemical processes, it is not easy to directly measure interaction forces between particles in a colloidal suspension. We propose an “Optical Bottle” approach to measure the colloidal osmotic compressibility of colloidal nanoparticles in a suspension.
The key to the optical bottle is to connect the nanoparticles’ thermodynamic property and the optical trapping behavior. Under an equilibrium trap, the osmotic pressure of the trapped particles is balanced by the external optical force. By analyzing the local particle number density enhancement, we can obtain the compressibility of trapped particles. Virial expansion of the osmotic compressibility of low concentration colloids yields virial coefficients of different orders, which reflect the changes of the sign and magnitude of the inter particle interaction. We studied the interaction between colloidal polystyrene nanospheres (100-200 nm in diameter) in the presence of polyethylene glycol (PEG) and salt (KCl).