Understanding the formation of different topologies of ring polymers at the molecular level reveals the key conditions (and obviously the driving forces) regarding end-structure and dynamics. Useful attempts to scrutinize the structure and dynamics of ring polymers at a molecular-level includes performing molecular simulations. In addition to the theoretical attempts, particle-based simulations comprise a great deal of studies of ring polymers such as molecular dynamics (MD) $^1$. All-atom MD simulations provide somewhat reliable results, but they are computationally expensive. Instead, simulations at larger length and longer time scales (for example, coarse-grained methods) provide a better relaxation of the rings and therefore can provide a better understanding of the experimental behavior  $^2$. Within coarse-grained simulations dissipative particle dynamics (DPD) $^3$ is a molecular simulation method widely used in simulating long time and length scales of soft matter. While DPD offers a wide usage field, significant drawbacks of the original method limits its applicability to a wider range of systems. The main focus of this project is to assess the applicability of DPD and extent the currently employed method to ring polymer systems. So far, DPD has not been heavily employed to simulate ring polymers. One of the two attempts $^{4, 5}$ was the work of Prof. Likos regarding the scaling and interactions of linear/ring polymers $^{5}$. However, the method still needs to be modified for its successful prediction of rheological properties under shear. Studying shear and rheological properties also require modeling of non-overlapping DPD particles (as a result of shear forces due to the soft nature of DPD potential) in addition to the bond crossing effects. Therefore, in this project the behavior of ring polymers under shear to observe the effect of hydrodynamics will be evaluated. Later, hydrodynamic consistency of the DPD method will be assessed and for the rings that are in different topologies. As a result of these steps, further development of the DPD potential to prevent the bead overlapping might be necessary. Finally, rheological properties will be quantified under applied shear with different shear rates applied. 

References

1.       R. Stano, J. Smrek and C. N. Likos, Acs Nano, 2023, 17, 21369–21382.
2.       L. Sappl, C. N. Likos and A. Zöttl, J Chem Phys, 2023, 159.
3.       P. J. Hoogerbrugge and J. M. V. A. Koelman, Europhys Lett, 1992, 19, 155–160.
4.       A. D. Goodson, J. E. Troxler, M. S. Rick, H. S. Ashbaugh and J. N. L. Albert, Macromolecules, 2019, 52, 9389–9397.
5.       M. Jehser, G. Zifferer and C. N. Likos, Polymers-Basel, 2019, 11.

Research Team: Christos N. Likos (U of Vienna) and Gokhan Kacar (Trakya U)

Dates of Stay: August 1 - September 1, 2026