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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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Tunability and Ordering in 2D Arrays of Magnetic Nanoparticles Assembled via Extreme Field Gradients
Abstract Colloidal magnetite nanoparticles self‐assemble onto a disk drive medium as directed by magnetic field gradients created where the medium magnetic moment switches direction over single nanometer distances. Here, it is shown that for two such reversals or transitions that are closely spaced, the nanoparticles self‐assemble into a single feature centered between the transitions, rather than forming separate features at the transitions, and the resulting 2D assembly achieves hexatic ordering. Langevin dynamics simulations are used to explain these results, and it is found that the detailed magnetic properties of the medium play a critical role in determining assembly location. Slight changes to solvent polarity disrupt the hexatic ordering and push the nanoparticles toward the transitions, suggesting an alternate mechanism to precisely tune the self‐assembly process.
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- PAR ID:
- 10371387
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials Interfaces
- Volume:
- 9
- Issue:
- 26
- ISSN:
- 2196-7350
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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