How do chiral active forces impact structure and dynamics of a ring polymer?

What is it about?

This paper presents the effect of chiral active forces on the structure and dynamics of a ring polymer. Using overdamped Langevin dynamics simulations in 2D, it has been shown that the chirality induces a significant amount of shrinkage in an active Brownian ring. The results indicate that the chirality induces local folding along the backbone of the polymer, thus it leads to a reduction in the structure. Along with the structural changes, chirality also promotes rotation of the ring's diameter vector. The rotation frequency follows power-law relation with the strength of the active force.

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Photo by Cmst May on Unsplash

Photo by Cmst May on Unsplash

Why is it important?

Due to the closed geometry, a ring polymer itself behaves very differently than the linear polymer. Recently, active rings have caught significant research interest along with the linear active chains. However, there is not much in the literature on a chiral active ring polymer. Nature has an abundance of chiral active particles, thus it is important to understand such systems of particles. This article covers a very important yet very unexplored research field. Using computer simulations, it studies the structural properties and dynamics of a chiral active ring. The radius of gyration of the ring reduces significantly as a function of the angular frequency controlling the chirality at a fixed active force. This reduction is due to the local folding of the ring along its contour which is shown using bond-correlation function. All being said, it must be noted that the non-monotonic behavior of the radius of gyration as a function of the active force does not change. Additionally, using the time correlation of the diameter vector, this paper shows that the diameter of the ring rotates on inclusion of chirality to the active forces. It also quantifies the rotation frequency and shows a power-law relation with strength of active force as $\nu \sim Pe^{3/2}$. The rotatory mean-squared dynamics of the monomers of the ring along with the rotation of the diameter vector, suggests an active tank-treading motion of the ring which is usually seen only in the presence of an external field such as shear.