Periodic Reporting for period 1 - RMAG (Rheology and Mechanics of Active Glasses)
Berichtszeitraum: 2020-11-01 bis 2022-10-31
The Problem Addressed: Dense living (active) matter systems are quite ubiquitous in nature, with examples ranging from the cytoplasm of cells to dense tissues of motile cells, from dense assembly of self propelled colloids to vehicular traffic jams. The mechanical behaviour of such dense living matter (aka active glassy matter) and how they flow under external mechanical perturbation are key to biological processes like wound healing or cancer metastasis etc., but today there is very limited understanding of what governs the mechanical/ rheological (flow) behaviour of such active glassy matter. Many recent studies have explored the dynamical and transport aspects of such active glasses, however, an understanding of the rheological behavior of these fascinating out-of-equilibrium systems remains elusive.
Application and importance to society: Beyond the fundamental research challenge mentioned above, that these questions present, an understanding of the rheology (i.e. mechanical and flow behaviour) of such dense living matter can also lead to design methods for functional materials such as 3D printed living tissue, assemblies of self propelled particles in granular experiments, disordered assemblies of driven colloids, active nanoclusters of magnetically driven nano machines etc.
Overall Objective: The primary aim of this MSCA project is to explore and better understand the mechanical and rheological responses, i.e. the material aspects of active glassy systems and thus to help design functional active glassy materials of practical interest.
Conclusion: Our study made crucial as well as substantial advancement in the theoretical understanding of dense living matter as well as sheds light in the rheological response of such material especially by discovering a novel type of ordering which can be potentially observed in such dense living systems.
Application and importance to society: Beyond the fundamental research challenge mentioned above, that these questions present, an understanding of the rheology (i.e. mechanical and flow behaviour) of such dense living matter can also lead to design methods for functional materials such as 3D printed living tissue, assemblies of self propelled particles in granular experiments, disordered assemblies of driven colloids, active nanoclusters of magnetically driven nano machines etc.
Overall Objective: The primary aim of this MSCA project is to explore and better understand the mechanical and rheological responses, i.e. the material aspects of active glassy systems and thus to help design functional active glassy materials of practical interest.
Conclusion: Our study made crucial as well as substantial advancement in the theoretical understanding of dense living matter as well as sheds light in the rheological response of such material especially by discovering a novel type of ordering which can be potentially observed in such dense living systems.
The work performed during the project has been divided into three parts as described below:
(i) In this work we explore glassy dynamics of dense assemblies of soft particles that are self-propelled by active forces. These forces have a fixed amplitude and a propulsion direction that varies on a timescale known as the the persistence timescale. Numerical simulations of such active glasses are computationally challenging when the dynamics is governed by large persistence times. We describe in detail our recently proposed scheme that allows one to study directly the dynamics in the large persistence time limit, on timescales around and well above the persistence time. We establish that our prescription faithfully reproduces all dynamical quantities in the appropriate limit when persistence time becomes extremely large.
The results has been published in: How to study a persistent active glassy system, R. Mandal and P. Sollich, J. Phys.: Condens. Matter, 33, 184001 (2021).
(ii) To explore the rheological response of such dense active matter system we employed extensive molecular dynamics simulation and a few distinct dynamical and mechanical order parameters. We have been able to differentiate three dynamical steady states in a sheared model active glassy system: 1) a disordered state, 2) a propulsion-induced ordered state, and 3) a shear-induced ordered state. We supplement these observations and make testable predictions for the joint distribution of single-particle position and orientation. with an analytical theory based on an effective single-particle Fokker–Planck description (with parameters that can be measured independently) to rationalize the existence of the shear-induced orientational ordering behavior in an active glassy system without explicit aligning interactions of, for example, Vicsek type. This ordering phenomenon occurs in the large persistence time limit and is made possible only by the applied steady shear.
The results has been published in: Shear Induced Orientational Ordering in an Active Glass Former, R. Mandal and P. Sollich, Proc. Natl. Acad. Sci., 118 (39) (2021).
(iii) To understand these dense active/living systems better we extended the active random first-order transition theory (ARFOT) in the high activity regime using an activity-dependent harmonic confining potential, which we solve self-consistently. The extended model predicts qualitative changes in the high activity regime, which agree with the results of simulations in both three-dimensional and two-dimensional models of active glass.
The results has been published in: The random first-order transition theory of active glass in the high-activity regime, R. Mandal, S.K. Nandi, C. Dasgupta, P. Sollich, Nir. S. Gov, J. Phys. Commun. 6 115001 (2022).
Also the results have been shared with the scientific community and beyond via Twitter, press release and scientific seminar, some of which are mentioned below:
Statistical Physics Webinar, Dept. of Phys. and Mat. Sci., Uni-Luxembourg, Luxembourg (2021)
Random Interactions Webinar, Department of Theoretical Physics, TIFR, India (2022).
German Physical Society (DPG) meeting at Regensburg, Germany (2022).
(i) In this work we explore glassy dynamics of dense assemblies of soft particles that are self-propelled by active forces. These forces have a fixed amplitude and a propulsion direction that varies on a timescale known as the the persistence timescale. Numerical simulations of such active glasses are computationally challenging when the dynamics is governed by large persistence times. We describe in detail our recently proposed scheme that allows one to study directly the dynamics in the large persistence time limit, on timescales around and well above the persistence time. We establish that our prescription faithfully reproduces all dynamical quantities in the appropriate limit when persistence time becomes extremely large.
The results has been published in: How to study a persistent active glassy system, R. Mandal and P. Sollich, J. Phys.: Condens. Matter, 33, 184001 (2021).
(ii) To explore the rheological response of such dense active matter system we employed extensive molecular dynamics simulation and a few distinct dynamical and mechanical order parameters. We have been able to differentiate three dynamical steady states in a sheared model active glassy system: 1) a disordered state, 2) a propulsion-induced ordered state, and 3) a shear-induced ordered state. We supplement these observations and make testable predictions for the joint distribution of single-particle position and orientation. with an analytical theory based on an effective single-particle Fokker–Planck description (with parameters that can be measured independently) to rationalize the existence of the shear-induced orientational ordering behavior in an active glassy system without explicit aligning interactions of, for example, Vicsek type. This ordering phenomenon occurs in the large persistence time limit and is made possible only by the applied steady shear.
The results has been published in: Shear Induced Orientational Ordering in an Active Glass Former, R. Mandal and P. Sollich, Proc. Natl. Acad. Sci., 118 (39) (2021).
(iii) To understand these dense active/living systems better we extended the active random first-order transition theory (ARFOT) in the high activity regime using an activity-dependent harmonic confining potential, which we solve self-consistently. The extended model predicts qualitative changes in the high activity regime, which agree with the results of simulations in both three-dimensional and two-dimensional models of active glass.
The results has been published in: The random first-order transition theory of active glass in the high-activity regime, R. Mandal, S.K. Nandi, C. Dasgupta, P. Sollich, Nir. S. Gov, J. Phys. Commun. 6 115001 (2022).
Also the results have been shared with the scientific community and beyond via Twitter, press release and scientific seminar, some of which are mentioned below:
Statistical Physics Webinar, Dept. of Phys. and Mat. Sci., Uni-Luxembourg, Luxembourg (2021)
Random Interactions Webinar, Department of Theoretical Physics, TIFR, India (2022).
German Physical Society (DPG) meeting at Regensburg, Germany (2022).
Our study explored one of the most unique and exotic out of equilibrium system that mimics living matter. We developed both numerical simulation technique and analytical theory to model, explore, control and explain such material and its mechanical and rheological behaviour. Often an external force or driving force destroys ordering in a system of particles. But our study demonstrates that the driving by shear flow is key in providing mobility to the particles that make up the active material, and it eventually leads to strong ordering phenomenon.
The results will open up exciting possibilities for researchers investigating the dynamical, mechanical and rheological responses of living matter to better understand the dynamics of cancerous tissues, motion of microbes in bacterial biofilms, ant assembly to name a few.
The results will open up exciting possibilities for researchers investigating the dynamical, mechanical and rheological responses of living matter to better understand the dynamics of cancerous tissues, motion of microbes in bacterial biofilms, ant assembly to name a few.