Chaos, mixing, and energy extraction in active nematics
Dr. Linda Hirst1, Professor
Co-PI(s): Kevin Mitchell1, Zvonimir Dogic2, Cristina Marchetti2
1: University of California, Merced, Merced, CA 95343
2: University of California, Santa Barbara, Santa Barbara, CA 93106
The objective of this project is to control the chaos and mixing in active materials, using a combination of experiment, simulation, and theory. Nature already provides many examples of active materials, from flocks of birds to sheets of cells and swarms of bacteria, but active materials are a new paradigm in soft condensed matter physics. In the lab, biomimetic and synthetic active materials have been developed, including self-propelled microparticles and dense phases of biomolecules driven by molecular motors. Although they are non-living, biomimetic active materials share the out-of-equilibrium property of living matter, i.e. they consume energy to maintain their complex structures. Such materials do not fit the framework of conventional thermodynamics, requiring new perspectives and techniques. This project focuses on active nematics, a particularly important class of active materials that consume energy to generate self-sustained flows. These active nematics represent a new class of fluids that exhibit spontaneous, self-driven mixing.
This project is a partnership between two minority serving University of California campuses. UC Merced is an R2 institution in the heart of the central valley of California: a historically underserved region. UC Merced will benefit by partnering with UC Santa Barbara, an R1 institution to build expertise and infrastructure in optical microscopy and micro-fabrication. This collaborative project injects a new perspective into the current understanding of active nematics by uniting concepts from fluid dynamics, chaos theory, and the mathematics of braids. The experimental work requires producing microtubule-based active nematics, using microfluidic techniques to be imaged under a microscope undergoing chaotic motion. The material can be confined in wells of various geometries, dramatically influencing defect dynamics. Various microprinted particles and shapes can also be inserted, both affecting and responding to the fluid flow. Microgears can be placed within the fluid to extract work and potentially perform useful functions.
The research will focus on two specific aims: 1. Tuning the self-mixing dynamics via engineering the boundaries of wells and via inserting motile microparticles. 2. Relating a form of entropy for the active nematics to the amount of work extracted. These aims will be approached in tandem using a synergistic combination of experiment and simulation. Current mathematical models do not account for all aspects of these experiments, and new simulation approaches will be developed and tested. Simulations will also guide experimental plans and be used to interpret experimental results. Compared to the long-established field of equilibrium materials, the field of active matter is still rapidly evolving, dominated by just a few materials. It is hoped that this work will spur interest in new synthetic materials using the principles of active nematics to drive self-mixing flows. Control of these self-mixing flows is the next step to achieve a useful new class of solvents. Such solvents might revolutionize micro-mixing technologies and produce novel biomimetic mixing environments.
This research was selected for funding by the Office of Basic Energy Sciences
