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6. Nanomotion of micro-objects driven by light-induced elastic waves on solid interfaces

Author

Lyu, Wei, Tang, Weiwei, Yan, Wei, and Qiu, Min

Subjects
Physics - Optics, Physics - Applied Physics
Abstract

It has been recently reported that elastic waves induced by nanosecond light pulses can be used to drive nano-motion of micro-objects on frictional solid interfaces, a challenging task for traditional techniques using tiny optical force. In this technique, the main physical quantities/parameters involved are: temporal width and energy of light pulses, thermal heating and cooling time, friction force and elastic waves. Despite a few experimental observations based on micro-fiber systems, a microscopic theory, which reveals how these quantities collaboratively enable motion of the micro-objects and derives what the underlying manipulation principles emerge, is absent. In this article, a comprehensive theoretical analysis--centralized around the above listed physical quantities, and illuminated by a single-friction-point model in conjunction with numerical simulations--is established to pedagogically clarify the physics. Our results reveal the two essential factors in this technique: (1) the use of short light pulses for rapid thermal expansion overwhelming friction resistance and (2) the timescale asymmetry in thermal heating and cooling for accumulating a net sliding distance. Moreover, we examine the effects of spatially distributed friction beyond the single-friction-point consideration, and show "tug-of-war"-like friction stretching in the driving process. Given these insights, we positively predict that this elastic-wave-based manipulation principle could be directly translated to micro/nano-scale optical waveguides on optical chips, and propose a practical design. We wish that these results offer theoretical guidelines for ongoing efforts of optical manipulation on solid interfaces with light-induced elastic waves.

Published
2023

8. Tautomerism unveils a self-inhibition mechanism of crystallization

Author

Tang, Weiwei, Yang, Taimin, Morales-Rivera, Cristian A, Geng, Xi, Srirambhatla, Vijay K, Kang, Xiang, Chauhan, Vraj P, Hong, Sungil, Tu, Qing, Florence, Alastair J, Mo, Huaping, Calderon, Hector A, Kisielowski, Christian, Hernandez, Francisco C Robles, Zou, Xiaodong, Mpourmpakis, Giannis, and Rimer, Jeffrey D

Subjects
Biochemistry and Cell Biology, Chemical Sciences, Biological Sciences
Abstract

Modifiers are commonly used in natural, biological, and synthetic crystallization to tailor the growth of diverse materials. Here, we identify tautomers as a new class of modifiers where the dynamic interconversion between solute and its corresponding tautomer(s) produces native crystal growth inhibitors. The macroscopic and microscopic effects imposed by inhibitor-crystal interactions reveal dual mechanisms of inhibition where tautomer occlusion within crystals that leads to natural bending, tunes elastic modulus, and selectively alters the rate of crystal dissolution. Our study focuses on ammonium urate crystallization and shows that the keto-enol form of urate, which exists as a minor tautomer, is a potent inhibitor that nearly suppresses crystal growth at select solution alkalinity and supersaturation. The generalizability of this phenomenon is demonstrated for two additional tautomers with relevance to biological systems and pharmaceuticals. These findings offer potential routes in crystal engineering to strategically control the mechanical or physicochemical properties of tautomeric materials.

Published
2023

23. Light-induced in-plane Rotation of Microobjects on Microfibers

Author

Lv, Wei, Tang, Weiwei, Yan, Wei, and Qiu, Min

Subjects
Physics - Optics, Physics - Applied Physics
Abstract

The transfer of angular momentum carried by photons into a microobject has been widely exploited to achieve the actuation of the microobject. However, this scheme is fundamentally defective in nonliquid environments as a result of the scale gap between friction forces ($\mu$N) and optical forces (pN). To bypass this challenge, the researchers have recently proposed to take advantage of elastic waves based on opto-thermo-mechanical effects [1-4]. Grounded on this insight, we here demonstrate and characterize the in-plane rotation of a gold nanoplate in its surface contacting with a microfiber, driven by nanosecond laser pulses, which has not been explored before. Furthermore, we examine the underlying physical mechanisms and highlight the essential role of the spatial gradient of optical absorption. The combined experimental and theoretical results offer new insights into the study of the light-induced actuation of the microobjects in nonliquid environments, an emerging field far from being mature in both comprehensive understanding and practical applications.

Published
2021

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