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

Advanced Optical Materials

et al. 2022

Self Cite

three-dimensionally manipulate micrometer-sized objects in solution in a nondestructive way, [1] optical tweezers have been used in research fields ranging from material science to biology. [2][3][4][5][6][7][8][9][10][11][12][13][14][15] Inside bulk solution, stable trapping is only achieved when the gradient force is larger than the scattering force and overcomes Brownian motion and gravity. [1] However, at an interface, the picture is completely different: both optical forces (gradient and scattering) assist in trapping and gathering of particles. The particles trapped inside the focus scatter and propagate the trapping laser, which expands the optical potential, in this way assisting in collecting particles outside the focus. Thus, so-called dynamically evolving assemblies of different materials (e.g., metallic and polymeric particles, proteins, small weight molecules) have been prepared by optical trapping at an interface. [16][17][18][19][20][21] In general, the morphology and the behavior of these trapped particles are dependent on the material properties; however, all these assemblies have in common that they expand far-beyond the irradiated area and that they are dynamic in owning to bespoke light-particle and particle-particle interactions.Gaining control on particle-particle interactions and selfassembled structures is one of the key objectives for colloidal Gaining control on particle-particle interactions and in this way on their (self )-assembled structures is essentialfor colloidal and material sciences. Currently, different strategies are described to achieve such control, however, all of them lack the spatiotemporal resolution required at the microscale. In this work, the potential of combining optical trapping and resonant photo excitation for modifying particle-particle interactions and subsequent assembling of dye-doped particles at the solution interface is demonstrated. The particle assemblies prepared by nonresonant 1064 nm optical trapping undergo morphology changes after resonant photoexcitation of the embedded dye molecules. Depending on the physicochemical properties of interface, quick hexagonal close packing (HCP)-rearrangement or explosive dispersion of assemblies is observed at air/solution (A/S) and glass/solution interfaces, respectively. By contrast, by resonant photoexcitation only, the dispersed dye-doped particles are pushed toward the A/S interface, followed by association to yield HCP-structured assemblies. The results are rationalized by considering the optical absorption force coupled with other nonoptical forces (e.g., capillary force, dipole-dipole or electrostatic repulsion) at the solution interface. Due to the inherent spatiotemporal properties of light and electronic transition of materials, absorption force is a unique element to control and modify the structural order of particle assemblies at interfaces.

Section: Resultsmentioning

confidence: 99%

The Optical Absorption Force Allows Controlling Colloidal Assembly Morphology at an Interface

Chang

Bresolí‐Obach

Advanced Optical Materials

et al. 2022

Self Cite

“…The NPs coming from the outside are trapped there, leading to the expansion of the assembly, which we call optically evolved assembling [52,56] . The assembling and rearrangement of NPs are driven by optical force, which is made possible by CW laser [77] . It will be fruitful to study these processes at solution surfaces by femtosecond laser.…”

Section: Summary and Perspectivementioning

confidence: 99%

Nanoparticle Assembling Dynamics Induced by Pulsed Optical Force

Chen

Chiang

et al. 2021

The Chemical Record

Self Cite

Femtosecond (fs) laser trapping dynamics is summarized for silica, hydrophobically modified silica, and polystyrene nanoparticles (NPs) in aqueous solution, highlighting their distinct optical trapping dynamics under CW laser. Mutually repulsive silica nanoparticles are tightly confined under fs laser compared to CW laser trapping and, upon increasing laser power, they are ejected from the focus as an assembly. Hydrophobically modified silica and polystyrene (PS) NPs are sequentially ejected just like a stream or ablated, giving bubbles. The ejection and bubbling take place with the direction perpendicular to laser polarization and its direction is randomly switched from one to the other. These characteristic features are interpreted from the viewpoint of single assembly formation of NPs at an asymmetric position in the optical potential. Temporal change in optical forces map is prepared for a single PS NP by calculating scattering, gradient, and temporal forces. The relative contribution of the forces changes with the volume increase of the assembly and, when the pushing force along the trapping pulse propagation overcome the gradient in the focal plane, the assembly undergoes the ejection. Further fs multiphoton absorption is induced for the larger assembly leading to bubble generation. The assembling, ejection, and bubbling dynamics of NPs are characteristic features of pulsed optical force and are considered as a new platform for developing new material fabrication method.

“…Later, we expanded this concept by optical trapping of MPs and nanoparticles (NPs) at interfaces. [ 19,23–25 ] Similar to the molecular case, trapped MPs/NPs at the focus scatter and propagate the trapping laser, expanding the optical potential outside the focal volume. For example, a disk‐like assembly is prepared for polystyrene (PS) MPs at the solution surface, growing up to an area larger than 150 μm 2 .…”

Section: Introductionmentioning

confidence: 99%

“…For example, a disk‐like assembly is prepared for polystyrene (PS) MPs at the solution surface, growing up to an area larger than 150 μm 2 . [ 24 ] At the early stages, the assembly presents a large dynamic motion with frequent “pistol‐like” MPs ejection. Instead, a periodical crystalline structure is prepared, when the PS NPs are trapped at the solution/glass interface.…”

Section: Introductionmentioning

confidence: 99%

“…For example, for the first time, multiplane widefield microscopy was used in 2020 to study the pistol‐like ejection dynamics of a PS MPs assembly. [ 24 ] On the other hand, dual‐objective lens microscope setups have been simultaneously used for both imaging and trapping purposes. [ 35–37 ] For example, a biological sample (zebrafish) was optically trapped using one objective while the other objective was used to image different regions and sections of the trapped biological sample.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Unraveling the three‐dimensional morphology and dynamics of the optically evolving polystyrene nanoparticle assembly using dual‐objective lens microscopy

Kamit

Tseng

et al. 2021

J Chinese Chemical Soc

Self Cite

Dynamically fluctuating assembly is prepared by trapping microparticles or nanoparticles at an interface. This phenomenon was previously described for 500 nm polystyrene nanoparticles optically trapped at water/glass interface, yielding a single disk‐like assembly, which size is much larger than the focal volume. In this work, we use a dual‐objective lens microscope to study the three‐dimensional shape and dynamics of such disk‐like assembly. The higher resolution of this system together with fast image acquisition (80 fps) rendered novel insights (e.g., particle fluctuation, assembly shape, interparticle distance, and so on), which could not be resolved using a conventional inverted microscope. These new insights will help to unravel the basis of this not yet fully understood “optically evolved phenomena,” which has a large potential in different research fields such as optical trapping, soft matter, and colloidal chemistry.