Exploring Conformations of Comb-like Polymers with Varying Grafting Density in Dilute Solutions Using Dissipative Particle Dynamics

Comb and bottlebrush polymers have shown potential as advanced materials for applications in polymer science due to the tunability of the polymer architecture. Tunable architectural parameters include: the density of grafted sidechains into the polymer backbone, σ , the backbone length, N_bb, and the sidechain length, N_sc. Grafting density has a strong effect on polymer conformations: as it varies from values characteristic of a linear polymer with no grafted chains (σ=0) to those of a bottlebrush (σ=1), comb-like polymers adopt stiffer conformations and the overall size of polymer increases. To predict the effect of the different molecular parameters on the conformations of comb-like polymers, scaling theories have been used. A free energy model in terms of exclude volume interactions and backbone’s elastic entropy has been proposed and used to describe experimental data, however the full validity of such free energy is still lacking. In this work, we have performed extensive simulations using Dissipative Particle Dynamics (DPD) and focused on two backbone lengths, N_bb=50, 100, and three sidechain lengths, N_sc=5, 10, 20, the grafting density was also varied from σ=0 to σ=1 . To quantify the effect of the different architectural parameters on polymer conformations we computed the gyration tensor, G_M, to obtain the relative shape anisotropy parameter A₃ , the asphericity, b, and the radius of gyration R_g. In addition, the backbone and sidechains end-to-end distances, the bond-bond correlation function, G(l) , and the Kuhn length were computed. Our results were compared to the scaling prediction (R_g/R_g,0)⁵∼(1+A₀σ+A₁σ²) proposed by Morozova and Lodge (2017)¹ for the experimental conformations of methylcellulose grafted with polyethylene glycol (PEG); our data was also compared to the scaling relation (R_g/R_g,0)-1∼(σN_sc)^0.66 obtained by Tang et al. (2022)² from Brownian Dynamics simulations.

1. Morozova, S.; Lodge, T. P., Conformation of Methylcellulose as a Function of Poly(ethylene glycol) Graft Density. ACS Macro Lett 2017, 6 (11), 1274-1279.

2. Tang, Z.; Pan, X.; Zhou, H.; Li, L.; Ding, M. J. M., Conformation of a Comb-like Chain Free in Solution and Confined in a Nanochannel: From Linear to Bottlebrush Structure. 2022.