2023 |
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 | Johnson, Keith E.; Montano, Brandon C.; Nambu, Kailino J.; Armstrong, Emilee N.; Cobb, Corie L.; Begley, Matthew R. Two-dimensional patterning of mesoscale fibers using acoustophoresis Journal Article In: Materials & Design, vol. 234, pp. 112328, 2023, ISSN: 0264-1275. Abstract | Links | Tags: acoustic focusing, acoustophoresis, periodic patterns @article{johnson_two-dimensional_2023,The performance of functional composites can rely critically on the arrangement of secondary phases; for example, patterned networks of conductive particles can impart anisotropic thermal, electric or ionic conductivity while preserving flexibility in the matrix. We demonstrate the use of standing acoustic waves to generate periodic patterns of short fibers. We extend the range of possible patterns with the first demonstration of both rectangular grids and arrays of octagons interspersed with rectangles. These newly demonstrated patterns are rationalized using theoretical models of acoustic forces and torques on fibers that account for two-dimensional spatial variations arising from applied acoustic fields. The models enable simulations of fiber motion, which are used to (i) map out final fiber positions as a function of initial position and orientation, and (ii) corroborate experiments visualizing fiber motion and final patterns. This approach provides a fast and accurate way to predict emergent fiber patterns as a function of excitation modality and fiber length. The theory and experiments clearly indicate strong coupling between the length of the fibers and the spacing of the acoustic nodes. This coupling is used to estimate reductions in percolation thresholds associated with the ratio of fiber length and acoustic wavelength. |
 | Johnson, Keith E.; Melchert, Drew S.; Armstrong, Emilee N.; Gianola, Daniel S.; Cobb, Corie L.; Begley, Matthew R. A simple, validated approach for design of two-dimensional periodic particle patterns via acoustophoresis Journal Article In: Materials & Design, pp. 112165, 2023, ISSN: 0264-1275. Abstract | Links | Tags: acoustic focusing, architechted materials, periodic patterns @article{johnson_simple_2023,Two-dimensional patterning of microparticles enables a wide range of functional materials, including patterned energy storage electrodes, flexible electronics, and sensor arrays. Particle patterning via acoustics offers an attractive path to generate a wide variety of 2D periodic patterns that introduce tailorable hierarchical porosity, useful for controlling surface area, transport distances, and other properties. This method is most effective with micron scale particles and patterns of tens to hundreds of microns. To enable systematic exploration of the broad design space for such patterns, this work develops a model of 2D and 3D assembly of particles at high loadings and validates the obtained patterns against both experiments and more computationally intensive modeling techniques. Using this simple model, connections are mapped between input parameters (like actuation conditions, particle volume fraction, material properties) and output geometrical features (like void size and shape, pattern connectivity, and surface area) so that they can be tailored to given applications. The utility of this simple model is illustrated by predicting and then experimentally demonstrating new hierarchical patterns resulting from multiple waves of different frequencies interacting. These multiscale patterns offer the potential to lift the limits on surface area, diffusion distances, and other features. |
2023 |
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| Two-dimensional patterning of mesoscale fibers using acoustophoresis Journal Article In: Materials & Design, vol. 234, pp. 112328, 2023, ISSN: 0264-1275. |
| A simple, validated approach for design of two-dimensional periodic particle patterns via acoustophoresis Journal Article In: Materials & Design, pp. 112165, 2023, ISSN: 0264-1275. |