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Passive and active tracer dynamics in crowded environment and in magnetic fluid:

Using molecular dynamics simulations we have investigated the tracer diffusion in a sea of polymers with specific binding zones for the tracer. These binding zones act as traps. Our simulations show that the tracer can undergo normal yet non-Gaussian diffusion under certain circumstances, e.g., when the polymers with traps are frozen in space and the volume fraction and the binding strength of the traps are moderate. In this case, as the tracer moves, it experiences a heterogeneous environment and exhibits confined continuous time random walk (CTRW) like motion resulting in a non-Gaussian behavior. Also the long time dynamics becomes subdiffusive as the number or the binding strength of the traps increases. However, if the polymers are mobile then the tracer dynamics is Gaussian but could be normal or subdiffusive depending on the number and the binding strength of the traps. In addition, with increasing binding strength and number of polymer traps, the probability of the tracer being trapped increases. On the other hand, removing the binding zones does not result in trapping, even at comparatively high crowding. Our simulations also showed that the trapping probability increases with the increasing size of the tracer and for a bigger tracer with the frozen polymer background the dynamics is only weakly non-Gaussian but highly subdiffusive. Our observations are in the same spirit as found in many recent experiments on tracer diffusion in polymeric materials and question the validity of using Gaussian theory to describe diffusion in a crowded environment in general. More recently, our group has worked on the tracer diffusion in polymer gel and in particular how size, shape of the tracer and the flexibility of the gel affect the dynamics and in particular on the emergence of non-Gaussian heavy tailed dynamics of the probe. In addition, we are currently investigating the dynamics of active Janus probe in crowded environment and the decoupling of its translational-rotational dynamics as observed at moderate crowding. Another related topic of research is controlling the diffusion of nanosized non-magnetic active particle in a magnetic fluid by external magnetic field.


Relevant Publications:

1. In Silico Studies of Active Probe Dynamics in Crowded Media - Ligesh Theeyancheri, Rajiblochan Sahoo, Praveen Kumar and Rajarshi Chakrabarti, ACS Omega 7, 33637 (2022). (Invited Mini-Review).


2. Chemically symmetric and asymmetric self-driven dumbbells in 2D polymer gel - Praveen Kumar, Ligesh Theeyancheri, and Rajarshi Chakrabarti Soft Matter 18, 2663 (2022).

3. Motion of an active particle with dynamical disorder - Koushik Goswami and Rajarshi Chakrabarti Soft Matter 18,  2332 (2022).

4. Transport of a self-propelled tracer through a hairy cylindrical channel: interplay of stickiness and activity - Rajiblochan Sahoo, Ligesh Theeyancheri and Rajarshi Chakrabarti, Soft Matter 18, 1310 (2022).

5. Directing the diffusion of a non-magnetic nanosized active particle with external magnetic fields - Martin Kaiser, Pedro A. Sanchez, Nairhita Samanta, Rajarshi Chakrabarti and Sofia S. Kantorovich, J. Phys. Chem. B 124, 8188 (2020).

6. Translational and rotational dynamics of a self-propelled Janus probe in crowded environments - Ligesh Theeyancheri, Subhasish Chaki, Nairhita Samanta, Rohit Goswami, Raghunath Chelakkot and Rajarshi Chakrabarti, Soft Matter 16, 8482 (2020).


7. Escape of a passive particle from activity-induced energy landscape: Emergence of slow and fast effective diffusion - Subhasish Chaki and Rajarshi Chakrabarti, Soft Matter 16, 7103 (2020). (This article has been featured in an online themed collection: Soft Matter Most Popular 2020).

8. Transport of probe particles in polymer network: effects of probe size, network rigidity and probe-polymer interaction - Praveen Kumar, Ligesh Theeyancheri, Subhasish Chaki and Rajarshi Chakrabarti, Soft Matter 15, 8992 (2019).

9. Tracer Diffusion in a sea of polymers with binding zones: Mobile vs frozen traps - Nairhita Samanta and Rajarshi Chakrabarti, Soft Matter, 12, 8554 (2016). (This article has been featured in an online themed collection: New Frontiers in Indian Research).

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