UC Santa Barbara

Acoustophoresis is an emerging method for tuning the microstructure in composites as a way to improve their functional properties. This method uses standing sound waves to push functional particles in a fluid to the pressure nodes of that field. That patterned arrangement is then transformed into a material with microstructure determined by the pattern of the acoustic field. Controlling the pattern of particles can 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 work explores a variety of improvements to the technique and develops models to allow for informed adjustment and improvement of these processes and patterns. In this work multiple new scalable processing methods are developed. Acoustophoretic direct ink writing is extended from single line printing to simultaneous deposition of many patterned microstructural features. This technique is developed on test materials mimicking the properties of Lithium ion battery electrodes and then successfully demonstrated with actual battery materials to generate large samples of cathodes with controlled microstructure enabling faster charging. This technique is then extended into a new approach which is used to rapidly form 2,400 cm2 of patterned particles. This represents an orders of magnitude increase in the scale of acoustics experiments which has previously been limited to several cm2. To better enable improvements in these systems,the motion of particles in non-newtonian fluids like the battery slurries are modeled using several classic rheological models. Both of these printing approaches generated linear micro-structures. To enable a wider range of microstructural features patterning of particles in multi-wave fields is also explored. A simple energy minimization model is proposed for predicting the patterns that form from high loadings of particles in arbitrary acoustic fields. This model is validated both with more complex discrete particle modeling and with experiments. Development of this model enabled the demonstration of new multi-scale hierarchical microstructures. To further increase microstructural control, systems utilizing fibers are investigated. Acoustic fields can control not only the position of fibers, but also their orientation. Patterning fibers in 2D fields is shown to form grid-like microstructures which span 2D space at very low loadings. Models were developed to describe the motion of fibers in 2D fields and predict what microstructures would form as a function of the applied field and fiber characteristics such as length. Understanding of microstructure gained from this modeling is used to design flexible conductive composites. Finally this work takes a broad look at all of the other existing approaches for manufacturing composites using acoustophoresis, and then proposes new motifs for enabling finer control of more aspects of microstructure in diverse materials systems.