# Flexible Conductive Composites with Programmed Electrical Anisotropy Using Acoustophoresis

## TL;DR

This paper introduces a novel acoustophoresis-based microstructural patterning technique for flexible, highly conductive composites that achieve anisotropic electrical properties with low filler loading, overcoming limitations of traditional methods.

## Contribution

The study demonstrates a new acoustophoresis method to pattern conductive fillers, enabling high conductivity, flexibility, and tunable anisotropy in composite materials with low filler content.

## Key findings

- Patterned composites reach 48% of bulk silver conductivity.
- Materials withstand over 500 bending cycles with minimal conductivity loss.
- Acoustophoresis enables control over electrical anisotropy in composites.

## Abstract

3D printing mechanically flexible composite materials with high electrical conductivity is currently hindered by the need to use high loading of conductive filler, which severely limits flexibility. Here, microstructural patterning of composite materials via acoustophoresis imparts these materials with high conductivity and flexibility simultaneously, filling a technology gap in the field. Acoustophoresis patterns filler particles into highly efficient percolated networks which utilize up to 97\% of the particles in the composite, whereas the inefficient stochastic networks of conventional dispersed-fiber composites utilize $<5$\%. These patterned materials have conductivity an order of magnitude higher than conventional composites made with the same ink, reaching 48\% the conductivity of bulk silver within the assembled silver-particle networks (at 2.6v\% loading). They also have low particle loading so that they're flexible, withstanding $>$500 bending cycles without losses in conductivity and changing conductivity only $5$\% within cycles on average (for 2.6v\% composites). In contrast, conventional unpatterned composites with the same conductivity require such high loading that they're prohibitively brittle. Finally, modulating the shape of the applied acoustic fields allows control over the anisotropy of the conductive networks and produces materials which are either 2-D conductive, 1-D conductive, or insulating, all using the same nozzle and ink.