Presentation Information
[10a-PA1-22]Sub-millimeter spoke-like assembly of polystyrene nanoparticles formed by optical trapping at air/solution interface
〇(M2)Ming-Lung Lau1, Mu-En Li1, Keisuke Yuzu1,2, Hiroshi Masuhara1 (1.National Yang Ming Chiao Tung Univ., 2.Kobe Univ.)
Keywords:
Polystyrene,Gold nanoparticle
Optical trapping at interfaces provides a versatile platform for investigating the assembly of nanoscale materials. 1) Here, we study optical trapping and assembling of polystyrene nanoparticles (PS NPs) of 100 nm diameter by focusing a 1064 nm laser at air/D2O interface of a suspension (45.5 particles/µm³). Spoke-like structures are formed under the conditions in Fig. 1(a–d), By linearly polarized (LP) laser irradiation, the spoke-like structures exhibited randomly distributed orientations, which is consistent with our previous report.2) In contrast, circularly polarized (CP) laser irradiation induced an asterisk-like morphology. It is worth noting that the assembly reaches up to the sub-millimeter scale along the interface and expands down to the bottom of the sample cell (~100 µm).
We reduced the laser power from 1 W to 500 mW and found no appreciable assembly formation. However, by adding a single gold (Au) NP at the focus, similar assembly formation was observed. Namely, Au NP-assisted assembling is demonstrated. With LP irradiation, spoke-like structures were clearly observed throughout the assembly, as shown in Fig. 1(f). However, under CP irradiation, no distinct spoke-like structures were observed within the central field of view, as shown in Fig. 1(g). By expanding the observation area, spoke-like structures could be identified farther from the focal spot, as shown in Fig. 1(h). Based on these results, we consider that scattering-light-induced optical force plays a more important role than the photothermal heating effect in the formation and growth of unique PS NPs assembly.
We reduced the laser power from 1 W to 500 mW and found no appreciable assembly formation. However, by adding a single gold (Au) NP at the focus, similar assembly formation was observed. Namely, Au NP-assisted assembling is demonstrated. With LP irradiation, spoke-like structures were clearly observed throughout the assembly, as shown in Fig. 1(f). However, under CP irradiation, no distinct spoke-like structures were observed within the central field of view, as shown in Fig. 1(g). By expanding the observation area, spoke-like structures could be identified farther from the focal spot, as shown in Fig. 1(h). Based on these results, we consider that scattering-light-induced optical force plays a more important role than the photothermal heating effect in the formation and growth of unique PS NPs assembly.