Activity induced phase separation and ordering in various model soft matter systems

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• Professor Prabal Maiti, Indian Institute of Science, Bangalore
• Wednesday 29 March 2023, 14:30-15:30
• Unilever Lecture Theatre, Yusuf Hamied Department of Chemistry & Zoom.

If you have a question about this talk, please contact Lisa Masters.

Theoretical Chemistry/Lennard-Jones Centre Seminar https://zoom.us/j/92447982065?pwd=RkhaYkM5VTZPZ3pYSHptUXlRSkppQT09

We report scalar activity induced phase separation and crystallization in a system of 3-d Lennard- Jones particles taken at state points spanning from gas to liquid regime using Molecular dynamics simulation (MD). Scalar activity was introduced by increasing the temperature of half of particles (labelled ‘hot’) while keeping the temperature of the other half constant at a lower value (labelled ‘cold’). The relative temperature difference between the two subsystems is considered as a measure of the activity. From our simulations we observe that the two species tend to phase separate at sufficiently high activity ratio. We observe similar activity induced phase separation in a mixture of active and passive dumbbells. We also study the order-disorder transition and phase separation in a mixture of hot and cold spherocylinder of different aspect ratio (L/D) interacting through Weeks-Chandler-Anderson (WCA) potential in three dimensions. Activity drives the cold particles through a phase transition to a more ordered liquid crystalline (LC) state and the hot particles to a state of less order compared to the initial equilibrium state. The cold components of a homogeneous isotropic (I) structure acquire nematic (N) and, at higher activity, crystalline (K) order. Similarly, the cold zone of a nematic initial state undergoes smectic (Sm) and crystal ordering above a critical value of activity while the hot component turns isotropic. Surprisingly, activity induces LC ordering for spherocylinders having aspect ratio below Onsager limit. We find that the hot particles occupy a larger volume and exert an extra kinetic pressure, confining, compressing and provoking an ordering transition of the cold-particle domains. Finally, we show similar activity induced phase separation and suppression of cholesteric phase in a chiral system.

References: 1. Scalar activity induced phase separation and liquid–solid transition in a Lennard-Jones system, S. S. N. Chari, C. Dasgupta and P. K. Maiti, Soft Matter, 2019, 15, 7275–7285. 2. Heating leads to liquid-crystal and crystalline order in a two-temperature active fluid of rods, J. Chattopadhyay, S. S. P. Sivajothi, K. Varma, S. Ramaswamy, C. Dasgupta and P. K. Maiti, PRE , 104, 054610 (2021) arXiv preprint arXiv:2105.04571 (2021) 3. Two temperature activity induces liquid crystal phase inaccessible in equilibrium, J. Chattopadhyay, S. S. P. Sivajothi, K. Varma, S. Ramaswamy, C. Dasgupta and P. K. Maiti, arXiv:2205.00667 (2022) 4. Phase behavior of active and passive dumbbells, Nayana V , Shiang-Tai Lin , Prabal K Maiti, arXiv preprint arXiv:2109.00415 (2021)

This talk is part of the Theory - Chemistry Research Interest Group series.

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