[19a-PA2-1~13] 3.1 Basic optics and frontier of optics

▲ [19a-PA2-5] Linearly Aligned Polystyrene Particles Ejected from Their Assembly during Laser Trapping at Air/Solution Interface

〇(M1)Jia-Syun Lu¹, Tetsuhiro Kudo¹, Hiroshi Masuhara^1,2 (1.Department of Applied Chemistry, National Chiao Tung Univ. Taiwan, 2.Center for Emergent Functional Matter Science, National Chiao Tung Univ. Taiwan)

Keywords:laser trapping, interface, polystyrene

Here, we demonstrate the experiment of the laser trapping of 1 µm PS particles at air/solution interface. The assembly looks like a concentric circle pattern due to interference of trapping laser at the interface. It is notable that several particles aligned linearly are ejected out from the assembly and its direction is same to that of the scattered light. We systematically change particle density and laser power, and use differently functionalized particles. The results show that higher particle density and higher laser power give more frequent ejection and more particles per each ejection. The particles with carboxylate surface (higher surface charge) are ejected more individually compared to those with sulfate ester one (lower surface charge). Here we propose two possible mechanisms for the ejection behavior based on light scattering and interparticle interaction. (I) When the assembly grows larger than the focus spot, the particles located at edge of the assembly receive stronger scattering force. Once the scattering force overcomes the gradient force, the particles are shot out of the assembly. (II) When the particles attracted toward the focus collide with the assembly, their momentum transfers to the assembly leading to the particles ejection.