Publications – InFab

2025
	Armstrong, Emilee N.; Johnson, Keith E.; Herbruger, Kyle A.; Sanchez, Austin K.; Begley, Matthew R.; Cobb, Corie L. Predicting multi-nodal in-nozzle particle interactions in high-viscosity fluid mediums for acoustophoretic direct-ink writing of line-patterned composites Journal Article In: Additive Manufacturing, vol. 106, pp. 104778, 2025, ISSN: 2214-8604. Abstract \| Links \| Tags: 3D printing, acoustic focusing, acoustophoresis, additive manufacturing @article{armstrong_predicting_2025, title = {Predicting multi-nodal in-nozzle particle interactions in high-viscosity fluid mediums for acoustophoretic direct-ink writing of line-patterned composites}, author = {Emilee N. Armstrong and Keith E. Johnson and Kyle A. Herbruger and Austin K. Sanchez and Matthew R. Begley and Corie L. Cobb}, url = {https://www.sciencedirect.com/science/article/pii/S2214860425001423}, doi = {10.1016/j.addma.2025.104778}, issn = {2214-8604}, year = {2025}, date = {2025-04-01}, urldate = {2025-04-01}, journal = {Additive Manufacturing}, volume = {106}, pages = {104778}, abstract = {Patterned functional materials offer improved properties (electrical, thermal, etc.) over their bulk counterparts in many applications, including energy storage, flexible electronics, and sensors. However, manufacturing approaches for patterning materials over large areas with features on the order of hundreds of microns or less are limited. Acoustophoresis, which uses acoustic forces to control particle arrangement in a fluid medium, is a pathway to address this challenge. This process is dependent on particle and fluid properties and enables patterning of a broad range of materials. Herein, a model with experimental validation is presented to demonstrate that acoustophoresis can be combined with direct-ink writing (DIW) to fabricate line patterns over large cm-scale areas. An in-nozzle particle interaction model was developed to investigate the impact of processing conditions on multi-nodal acoustophoretic DIW. The model predicts patterned line widths within a factor of two relative to experimental results for a high viscosity case study. The model was used to investigate the impact of frequency, particle loading, particle radius, and acoustic pressure on line width and patterning time, providing critical feedback regarding the processing conditions suitable for a target application. Model results illustrate that frequency has the greatest impact on line patterns: increasing from 1 to 3MHz resulted in a greater than 65% reduction in line width and a greater than 85% reduction in patterning time. Additionally, experiments were conducted with an alumina-epoxy ink, and a textasciitilde21 cm2 area pattern was rastered in textasciitilde5.5minutes, demonstrating a path towards large-area line-patterned composite fabrication.}, keywords = {3D printing, acoustic focusing, acoustophoresis, additive manufacturing}, pubstate = {published}, tppubtype = {article} } Close Patterned functional materials offer improved properties (electrical, thermal, etc.) over their bulk counterparts in many applications, including energy storage, flexible electronics, and sensors. However, manufacturing approaches for patterning materials over large areas with features on the order of hundreds of microns or less are limited. Acoustophoresis, which uses acoustic forces to control particle arrangement in a fluid medium, is a pathway to address this challenge. This process is dependent on particle and fluid properties and enables patterning of a broad range of materials. Herein, a model with experimental validation is presented to demonstrate that acoustophoresis can be combined with direct-ink writing (DIW) to fabricate line patterns over large cm-scale areas. An in-nozzle particle interaction model was developed to investigate the impact of processing conditions on multi-nodal acoustophoretic DIW. The model predicts patterned line widths within a factor of two relative to experimental results for a high viscosity case study. The model was used to investigate the impact of frequency, particle loading, particle radius, and acoustic pressure on line width and patterning time, providing critical feedback regarding the processing conditions suitable for a target application. Model results illustrate that frequency has the greatest impact on line patterns: increasing from 1 to 3MHz resulted in a greater than 65% reduction in line width and a greater than 85% reduction in patterning time. Additionally, experiments were conducted with an alumina-epoxy ink, and a textasciitilde21 cm2 area pattern was rastered in textasciitilde5.5minutes, demonstrating a path towards large-area line-patterned composite fabrication. Close https://www.sciencedirect.com/science/article/pii/S2214860425001423 doi:10.1016/j.addma.2025.104778 Close
2023
	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, title = {Two-dimensional patterning of mesoscale fibers using acoustophoresis}, author = {Keith E. Johnson and Brandon C. Montano and Kailino J. Nambu and Emilee N. Armstrong and Corie L. Cobb and Matthew R. Begley}, url = {https://www.sciencedirect.com/science/article/pii/S0264127523007438}, doi = {10.1016/j.matdes.2023.112328}, issn = {0264-1275}, year = {2023}, date = {2023-10-01}, urldate = {2023-10-01}, journal = {Materials & Design}, volume = {234}, pages = {112328}, abstract = {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.}, keywords = {acoustic focusing, acoustophoresis, periodic patterns}, pubstate = {published}, tppubtype = {article} } Close 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. Close https://www.sciencedirect.com/science/article/pii/S0264127523007438 doi:10.1016/j.matdes.2023.112328 Close
	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, title = {A simple, validated approach for design of two-dimensional periodic particle patterns via acoustophoresis}, author = {Keith E. Johnson and Drew S. Melchert and Emilee N. Armstrong and Daniel S. Gianola and Corie L. Cobb and Matthew R. Begley}, url = {https://www.sciencedirect.com/science/article/pii/S0264127523005804}, doi = {10.1016/j.matdes.2023.112165}, issn = {0264-1275}, year = {2023}, date = {2023-07-20}, urldate = {2023-07-01}, journal = {Materials & Design}, pages = {112165}, abstract = {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.}, keywords = {acoustic focusing, architechted materials, periodic patterns}, pubstate = {published}, tppubtype = {article} } Close 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. Close https://www.sciencedirect.com/science/article/pii/S0264127523005804 doi:10.1016/j.matdes.2023.112165 Close