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Ultrasound directed self-assembly (DSA) allows organizing particles dispersed in a fluid medium into user-specified patterns, driven by the acoustic radiation force associated with a standing ultrasound wave. Accurate control of the spatial organization of the particles in the fluid medium requires accounting for medium viscosity and particle volume fraction. However, existing theories consider an inviscid medium or only determine the effect of viscosity on the magnitude of the acoustic radiation force rather than the locations where particles assemble, which is crucial information to use ultrasound DSA as a fabrication method. We experimentally measure the deviation between locations where spherical microparticles assemble during ultrasound DSA as a function of medium viscosity and particle volume fraction. Additionally, we simulate the experiments using coupled-phase theory and the time-averaged acoustic radiation potential, and we derive best-fit equations that predict the deviation between locations where particles assemble during ultrasound DSA when using viscous and inviscid theory. We show that the deviation between locations where particles assemble in viscous and inviscid media first increases and then decreases with increasing particle volume fraction and medium viscosity, which we explain by means of the sound propagation velocity of the mixture. This work has implications for using ultrasound DSA to fabricate, e.g., engineered polymer composite materials that derive their function from accurately organizing a pattern of particles embedded in the polymer matrix.
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Multi‐Frequency Ultrasound Directed Self‐Assembly
Abstract Ultrasound‐directed self‐assembly (DSA) utilizes the acoustic radiation force associated with a standing ultrasound wave field to organize particles dispersed in a fluid medium into specific patterns. State‐of‐the‐art ultrasound DSA methods use single‐frequency ultrasound wave fields, which only allow organizing particles into simple, periodic patterns, or require a large number of ultrasound transducers to assemble complex patterns. In contrast, this work introduces multi‐frequency ultrasound wave fields to organize particles into complex patterns. A method is theoretically derived to determine the operating parameters (frequency, amplitude, phase) of any arrangement of ultrasound transducers, required to assemble spherical particles dispersed in a fluid medium into specific patterns, and experimentally validated for a system with two frequencies. The results show that multi‐frequency compared to single‐frequency ultrasound DSA enables the assembly of complex patterns of particles with substantially fewer ultrasound transducers. Additionally, the method does not incur a penalty in terms of accuracy, and it does not require custom hardware for each different pattern, thus offering reconfigurability, which contrasts, e.g., acoustic holography. Multi‐frequency ultrasound DSA can spur progress in a myriad of engineering applications, including the manufacturing of multi‐functional polymer matrix composite materials that derive their structural, electric, acoustic, or thermal properties from the spatial organization of particles in the matrix.
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- PAR ID:
- 10515469
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Advanced Functional Materials
- ISSN:
- 1616-301X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Ultrasound directed self-assembly (DSA) utilizes the acoustic radiation force (ARF) associated with a standing ultrasound wave to organize particles dispersed in a fluid medium into specific patterns. The ARF is a superposition of the primary acoustic radiation force, which results from the incident standing ultrasound wave, and the acoustic interaction force, which originates from single and multiple scattering between neighboring particles. In contrast with most reports in the literature that neglect multiple scattering when calculating the ARF, we demonstrate that the deviation between considering single or multiple scattering may reach up to 100%, depending on the ultrasound DSA process parameters and material properties. We evaluate a theoretical case with three spherical particles in a viscous medium and derive operating maps that quantify the deviation between both scattering approaches as a function of the ultrasound DSA process parameters. Then, we study a realistic system with hundreds of particles dispersed in a viscous medium, and show that the deviation between the ARF resulting from single and multiple scattering increases with decreasing particle size and increasing medium viscosity, density ratio, compressibility ratio, and particle volume fraction. This work provides a quantitative basis for determining whether to consider single or multiple scattering in ultrasound DSA simulations.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1002/adfm.202400193
