# Neuromorphic Liquid Marbles With Aqueous Carbon Nanotube Cores

## TL;DR

This paper presents a novel neuromorphic liquid marble device with aqueous carbon nanotube cores that exhibits memristive switching behavior, mimicking synaptic properties for potential use in unconventional computing.

## Contribution

The development of liquid marbles with neuromorphic properties using copper coatings and carbon nanotube cores, demonstrating reversible resistance switching and memristive behavior.

## Key findings

- Resistance can be switched between high and low states with 88% reduction after entrainment.
- Switching is reversible and strengthened with repeated stimuli.
- Liquid marbles exhibit memristor-like hysteresis IV profiles.

## Abstract

Neuromorphic computing devices attempt to emulate features of biological nervous systems through mimicking the properties of synapses, towards implementing the emergent properties of their counterparts, such as learning. Inspired by recent advances in the utilisation of liquid marbles (microlitre quantities of fluid coated in hydrophobic powder) for the creation of unconventional computing devices, we describe the development of liquid marbles with neuromorphic properties through the use of copper coatings and 1.0 mg/ml carbon nanotube-containing fluid cores. Experimentation was performed through sandwiching the marbles between two cup-style electrodes and stimulating them with repeated DC pulses at 3.0 V. Our results demonstrate that `entrainment' of a carbon nanotube filled-copper liquid marble via periodic pulses can cause their electrical resistance to rapidly switch between high to low resistance profiles, upon inverting the polarity of stimulation: the reduction in resistance between high and low profiles was approximately 88\% after two rounds of entrainment. This effect was found to be reversible through reversion to the original stimulus polarity and was strengthened by repeated experimentation, as evidenced by a mean reduction in time to switching onset of 43\%. These effects were not replicated in nanotube solutions not bound inside liquid marbles. Our electrical characterisation also reveals that nanotube-filled liquid marbles exhibit pinched loop hysteresis IV profiles consistent with the description of memristors. We conclude by discussing the applications of this technology to the development of unconventional computing devices and the study of emergent characteristics in biological neural tissue.