Convection Dynamics Forced by Optical Trapping with a Focused Laser Beam

Hosokawa, Chie; Tsuji, Tetsuro; Kishimoto, Tatsunori; Okubo, Takumi; Kudoh, Suguru N.

doi:10.1021/acs.jpcc.9b11663

Cited by 21 publications

(16 citation statements)

References 32 publications

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“…The optical force value and its direction change from position to position and time to time. Another reason may be related to the thermal effect, ,, as the focused high-intensity laser irradiation always results in local heating, although we use D 2 O to avoid the 1064 nm absorption by the solvent. The spatial distribution of the mechanical rigidity and refractive index of the assembly, as well as heating effects, must be dynamically balanced with each other, which is important for understanding the pistol-like ejection with a small angle distribution.…”

Section: Discussionmentioning

confidence: 99%

Optical Force-Induced Dynamics of Assembling, Rearrangement, and Three-Dimensional Pistol-like Ejection of Microparticles at the Solution Surface

Kudo

Louis

et al. 2020

J. Phys. Chem. C

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Optical trapping and assembling dynamics of polystyrene (PS) microparticles (MPs) of 1 µm diameter is studied at its solution-air surface using a widefield microscope. Upon switching on the intense 1064 nm laser, the MPs are gathered, forming a single concentric circle (CC)-like assembly larger than the focus. It consists of a few tens of MPs and the central part of the assembly shows structural color, which indicates that the assembly is also growing in the axial direction. The MPs are dynamically fluctuating in inside the assembly, and some of them are ejected when newly coming MPs collide with the CC-like assembly from the bulk solution.The MPs speedily leaving the assembly are aligned in a linear manner, which we refer to as "pistole-like ejection". The three-dimensional (3D) dynamics was elucidated by changing laser power, MP concentration, and surface chemical property. It is directly observed that the trapping laser was scattered radially from the CC-like assembly and the ejection was induced along the scattered laser path. This pistol-like ejection is stochastically repeated upon the collision. After prolonged irradiation, the assembly rearranges to a hexagonal close packing (HCP)-like assembly, in which no pistol-like ejection was observed. We note that our observation is characteristic of the solution surface and were never observed in bulk solution.We conclude that the kinetically driven assembly formation gives rise to a CC-like structure which is meta-stable and shows the pistol-like ejection phenomenon. Later, the assembly rearranges to a thermodynamically stable HCP-like assembly. The assembling, pistol-like ejection, and its rearrangement are all driven by optical force, which is common for optical trapping-induced molecular crystallization and optically evolved assembling and swarming of gold nanoparticles (NPs).

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Section: Discussionmentioning

confidence: 99%

Optical Force-Induced Dynamics of Assembling, Rearrangement, and Three-Dimensional Pistol-like Ejection of Microparticles at the Solution Surface

Kudo

Louis

et al. 2020

J. Phys. Chem. C

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“…In the sample cell with non-absorbing reflective film, the laser is mainly absorbed by water, and the temperature increase is 1.4 °C -1.9 °C /100 mW for 1064 nm laser [47]. Although the temperature increase has an effect on the optical trapping force [48,49], this effect can generally be ignored, and the convective drag force and the thermophoretic force can be ignored. Thus, Equation (2) becomes Ftrap = FoS.…”

Section: Trapping Forces Of Optical Trap and Optothermal Trapmentioning

confidence: 99%

Experimental Study of Transverse Trapping Forces of an Optothermal Trap Close to an Absorbing Reflective Film

et al. 2022

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The optothermal manipulation of micro-objects is significant for understanding and exploring the unknown in the microscale word, which has found many applications in colloidal science and life science. In this work, we study the transverse forces of an optothermal trap in front of a gold film, which is an absorbing reflective surface for the incident laser beam. It is demonstrated that optothermal forces can be divided into two parts: optical force of a standing-wave trap, and thermal force of a thermal trap. The optical force of the standing-wave trap can be obtained by measuring the optical trapping force close to a non-absorbing film with same reflectance. The thermal force can be obtained by subtracting the optical force of the standing-wave trap from the total trapping force of the optothermal trap close to the gold film. The results show that both optical and thermal trapping forces increase with laser power increasing. The optical trapping force is larger than the thermal trapping force, which is composed of convective drag force and thermophoretic force. Further experiment is run to study the composition of thermal force. The result shows that the convective flow is generated later than the thermophoretic flow. The results proposed here are useful for enabling users to optimize optothermal manipulation method for future applications.

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“…Indeed, a molten assembly of PS NPs was prepared by long-term irradiation (SI). This means that a convection flow in the solution should be involved, , and it may transfer small 1 μm PS NPs from the surrounding area to the center or to the surface of the MP. Another temperature effect discussed frequently in laser trapping is the thermophoretic effect. , NPs and MPs are rapidly transferred from the heated focal volume to the surrounding, which compensates the temperature difference.…”

Section: Resultsmentioning

confidence: 99%

Anomalously Large Assembly Formation of Polystyrene Nanoparticles by Optical Trapping at the Solution Surface

Wang

Kudo

et al. 2020

Langmuir

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We demonstrated the optical trapping-induced formation of a single large disc-like assembly (∼50 μm in diameter) of polystyrene (PS) nanoparticles (NPs) (100 nm in diameter) at a solution surface. Different from the conventional trapping behavior in solution, the assembly grows from the focus to the outside along the surface and contains needle structures expanding radially in all directions. Upon switching off the trapping laser, the assembly disperses and needle structures disappear, while the highly concentrated domain of the NPs is left for a while. The single assembly is quickly restored by switching on the laser again, where the needle structures are also reproduced but in a different way. When a single 10 μm PS microparticle (MP) is trapped in the NP solution, a single disc-like assembly containing needle structures is similarly prepared outside the MP. Based on backscattering imaging and tracking analyses of the MP at the solution surface, it is proposed that scattering and propagation of the trapping laser from the central part of the NP assembly or the MP lead to this new phenomenon.

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Convection Dynamics Forced by Optical Trapping with a Focused Laser Beam

Cited by 21 publications

References 32 publications

Optical Force-Induced Dynamics of Assembling, Rearrangement, and Three-Dimensional Pistol-like Ejection of Microparticles at the Solution Surface

Optical Force-Induced Dynamics of Assembling, Rearrangement, and Three-Dimensional Pistol-like Ejection of Microparticles at the Solution Surface

Experimental Study of Transverse Trapping Forces of an Optothermal Trap Close to an Absorbing Reflective Film

Anomalously Large Assembly Formation of Polystyrene Nanoparticles by Optical Trapping at the Solution Surface

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