Structure and dynamics in active glass-forming liquids

Project Information

ARIADNE

Grant agreement ID: 840195

DOI

10.3030/840195

Project closed

EC signature date 10 April 2019

Start date 1 June 2019

End date 31 May 2021

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 160 932,48

EU contribution

€ 160 932,48

Coordinated by

UNIVERSIDAD DE GRANADA
Spain

Periodic Reporting for period 1 - ARIADNE (Structure and dynamics in active glass-forming liquids)

Reporting period: 2019-06-01 to 2021-05-31

Summary of the context and overall objectives of the project

Transport in passive systems such as molecular liquids is controlled by temperature. In contrast, active systems such as bacterial colonies present a new control parameter in the form of a non-thermal energy. This energy, used by active particles to drive their motion, is accompanied by a variety of particle features, including different shapes and interactions. It is unclear how this scenario conditions transport and phase transitions in these systems. The overall aim of this project is to characterise this transport for a collection of models of active systems using molecular dynamics simulations and experimental techniques. This investigation is conceived to provide a foundation, based on canonical models and specially designed experiments, for exploring complex biological environments.

This project introduces many original aspects such as the use of a novel mixed methodology, including coarse grained models, a repertoire of statistical tools, and the use of experimental techniques so far employed in passive systems. This mixing of different techniques and disciplines favours an innovative transfer of knowledge between physicists and biologists. The project also promotes some of the aspirations of the MSCA: the engagement of the general public through a pedagogical dissemination and the establishment of interdisciplinary interchanges.

This project is included in an emergent field of fundamental research resulting from combining different disciplines such as statistical physics and microbiology. These hybrid collaborations have shown great impact, reaching different expert audiences and bringing new perspectives to problems that were tackled from a single perspective. Thus, this project has created a networking initiative, involving different departments at the University of Granada, collaborations with companies, and connections with other international institutions. With this project we have also considered some of the challenges promoted by the United Nations: the development of resilient and diversified human structures to foster innovation.

As overall objectives, this project considered the study of transport in real systems and computational models with: isotropic interactions, non-isotropic interactions, and polarity. Despite the original objectives of this project (in particular those concerning experiments) have strongly suffered from the situation created by the COVID-19, this action has concluded with significant results: i) all the computational models were developed; ii) despite the lockdown arriving to Spain at the end of the first third of the action, I obtained promising experimental results; iii) I published a research paper as leading scientist in Physical Review X (the journal with the second highest impact factor, 15.762 publishing research in all areas of physics), and have three papers in preparation; iv) I developed a network of collaborations of different kind: local, international, interdisciplinary, and inter-sectoral; v) I communicated my results in international conferences, and in internal and external seminars; vi) I disseminated my expertise by: teaching courses at an undergraduate level, considering the gender dimension through activities with secondary schools, and being present in the media.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

I first developed computational models of: i) active particles with isotropic interaction in 2D and 3D; ii) active particles with non-isotropic interactions; iii) elongated active particles. Second, I performed dynamic light scattering experiments using E. coli bacteria.

With the models presenting isotropic and non-isotropic interactions, I obtained remarkable results: i) their rare events dynamics, which controls the glass transition, not only depends on the system dimension but also on the temperature; ii) I showed that, contrary to the classical theory of Brownian motion, these systems present distributions of displacements which evolve diffusively being non-Gaussian. I also explored the model for elongated particles and see that it explains the diffusion observed in real E. coli bacterial colonies.

Since it was not possible to do experimental work due to the closing of the university at the end of the first third of the action, I started three (remote) collaborations to tackle other related problems from a computational/theoretical perspective: i) a collaboration with a researcher of the Complutense University of Madrid on the growth of aggregates of active particles, where we observed three growing regimes never included before in a single model: exponential, power law, and linear; ii) a collaboration with researchers from Potsdam University, Humboldt University, and the University of Vienna, where we verified the emergence of correlations between rare events in isotropic systems; iv) a collaboration with researchers of CSIC on a model of gel which shows directional patterns without introducing directionality in the interaction.

These results have been communicated by different ways: i) our results on rare events dynamics have been published in Physical Review X, with me as corresponding author, and has been presented in two international conferences and one seminar; ii) the three collaborations mentioned above are contained in three papers in preparation; iii) the work with elongated particles has produced a BSc thesis in which I am the only supervisor, being included in the top 2% of the BSc thesis presented in 2021. Apart from that, I have disseminated my results, as well as other topics belonging to my field of expertise, to graduate students, secondary schools, and through the media.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

We have shown that the rare events dynamics of the studied systems is non-universal, depending on the system dimension and on the temperature. These systems also show a Brownian yet non-Gaussian regime, whose existence contrasts with the classical theory of Brownian motion. These significant findings also contrast with the current theories, opening new research avenues. We expect to see our results manifested in a large variety of systems such as colloidal glasses and gels, granular systems, complex biological media controlled by pH, and other non-equilibrium active systems such as cells in migration processes or organelles in the cytoplasm of animal cells. Our model for elongated particles showed the capability for capturing some relevant features manifested in the transport of real E coli bacteria, making it an optimal candidate to study experimentally collective behaviour.

This project had great impact in stimulating new collaborations. These collaborations currently involve researchers from Potsdam, Humboldt, and Leiden Universities, Okinawa Institute of Technology, and the University of Vienna. The project also established national collaborations with researches of CSIC and other departments inside the university of Granada (microbiology). With this project I also established a collaboration with Zetalabs, a company that uses AI solutions in agriculture.

The impact of publishing in a top journal will presumably improve my future funding and the funding received by the research group in which I am inserted. The results of my research have even been covered by the local media. In conclusion, the outputs of this project have manifested through new collaborations with different sectors and consolidated my situation towards a permanent faculty position in Granada.

Sandalo Roldan-Vargas