Hydrodynamics of active odd elastic matter

Publication by Ruben Lier, Jay Armas, Stefano Bo, Charlie Duclut, Frank Jülicher, and Piotr Surówka can be found here.

Almost all materials in nature exhibit some form of elasticity in certain regimes. Despite being a centuries old subject, it was recently shown that the traditional methods of elasticity theory need to be revisited in order to be able to describe activity (e.g. self-driven agents such as bacteria) – see Odd Elasticity. The main goal of this proposal is to understand what happens when such materials start flowing. In other words, it aims at developing a hydrodynamic theory of new potential phase of matters - active and odd elastic materials – as well as exploring experimental setups using metamaterials. 

In recent years, active matter hydrodynamic equations have played a very important role in understanding pattern formation and flocking in birds, animals, and fishes. The close relationship between the continuum model equations of active matter and those describing liquid crystals has stimulated new directions of research for physicists over the last quarter-century. Recently, such approaches have been extended to include the effect of chirality of the active agents. In real biological systems, there are various examples in which chirality emerges naturally, such as in the swimming strokes of sperm cells. Consequently, successful modeling of chirality in the active matter equations has become a clear milestone to be achieved in the study of active matter, including modifications of active matter hydrodynamics.

A second hot-topic area in the investigation of active matter has been by using equations of motion that break Newton’s third law. The idea of breaking Newton’s third law might sound fanciful, but considering interaction between active agents which carry their own energy source this is a potential reality. As a result, the investigation

of non-reciprocity both in the field of active matter and elsewhere is a burgeoning field of ongoing research. In particular, bringing together the two threads introduced here, the combination of chirality and non-reciprocity leads to the presence of novel response functions like odd viscosity and odd elasticity. This NWA project aims at studying the effect on these and other response functions as uncovered in the solutions of the hydrodynamic equations.

To be more specific, the project plans are: (1) to investigate numerically and analytically the hydrodynamic

equations of chiral active matter for the flow structures that emerge in these systems; (2) to develop and investigate the hydrodynamic equations of certain classes of non-reciprocal active matter to study flow structures using effective field theory methods; (3) to investigate the emergence and the phenomenology of odd viscosity and odd elasticity in active matter systems using both analytical and numerical methods; (4) to devise potential experimental setups using metamaterials.

Recent study of non-reciprocal active materials and chiral materials have shown how these materials can display a wide range of novel behaviors. This proposal centers on studying the behavior of new classes of active materials and in the development of their comprehensive theoretical understanding.

This project will be done in collaboration with Dr. Jay Armas (UvA), who studies viscoelasticity from a high-energy physics theory point of view; Dr. Corentin Coulais (UvA), who is a leading experimentalist in the field of non- reciprocal systems; Dr. Sara Jabbari Farouji (UvA) who works on simulating the hydrodynamics of active swimmers and Dr. Luca Giomi (U.Leiden) who works on active liquid crystal hydrodynamics.