Modelling active emulsions and shells

Modelling active emulsions and shells

Supervisors: Kevin Stratford,  Davide Marenduzzo (School of Physics and Astronomy)

Project description:

Mixtures of active and passive fluids are systems of interest both fundamentally, owing to their non-equilibrium nature, and in technology, which may benefit from their potential for self-assembly into useful structures. These systems can be built in the laboratory starting from suspensions of molecular motors and cytoskeletal filaments, either in water or in water-in-oil emulsions [1,2]. In the latter case, addition of a non-absorbing polymer such as polyethylene-glycol (PEG) causes the active material to migrate to oil-water interfaces, probably owing to depletion interactions mediated by PEG.

We would like to extend the Ludwig [3] code developed by EPCC: first, to the study of binary systems made up by active nematics and isotropic fluids, and second to ternary systems where an active nematic fluid self-assembles at the interfaces between two passive fluids (such as oil and water). This thin layer is an "active shell". These systems are fully 3-dimensional, and this, coupled to the complex nature of the tensor order parameters which describe the nematic structure in the active phase, renders numerical studies particularly challenging.

Besides extending the Ludwig code (used for passive mixtures, e.g. in [4]) to capture the activity of one of the components, and to recreate the self-assembly of active shells, we will need large-scale parallel simulations to make inroads in this problem. It would be of interest to also pursue both CPU-based and GPU-based simulations, which will stress the need for a performance portable implementation. EPCC has access to both large CPU-based and GPU-based systems. The results would constitute the very first fully 3D study of composite materials with an active component.

Student Requirements:

  • A UK 2:1 honours degree, or its international equivalent, in a relevant subject such as computer science and informatics, physics, mathematics, engineering, biology, chemistry and geosciences.
  • You must be a competent programmer in at least one of C, C++, Python, Fortran, or Java and should be familiar with mathematical concepts such as algebra, linear algebra and probability and statistics.
  • You must demonstrate a level of English language competency that will enable you to succeed in your studies (further information available here: https://www.ed.ac.uk/studying/postgraduate/applying/your-application/entry-requirements/english-requirements)

Desirable Skills and Experience

  • Some knowledge of numerical simulation and computational fluid dynamics.
  • Experience with numerical simulation and programming in C.

References

[1] T. Sanchez, D. T. Chen, S. J. De Camp, M. Heymann, Z. Dogic, Nature 491, 431 (2012).

[2] B. Martinez-Prat, J. Ignes-Mullol, J. Casademunt, F. Sagues, Nat. Phys. 15, 362 (2019).

[3] See https://github.com/ludwig-cf/ludwig

[4] J. Lintuvuori, K. Stratford, M. E. Cates, D. Marenduzzo, Phys. Rev. Lett. 121, 037802 (2018).

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