The Concentration Dependence of the Size and Symmetry of a Bottlebrush Polymer in a Good Solvent

Published

August 7, 2020

Author(s)

Daniel F. Sunday, Alexandros Chremos, Tyler B. Martin, Alice B. Chang, Adam B. Burns, Robert H. Grubbs

Abstract

Bottlebrush polymers consist of a linear backbone with densely grafted sidechains which impact the rigidity of the molecule. The persistence length of the bottlebrush backbone in solution is influenced by both the intrinsic structure of the polymer and by the local environment, such as the solvent quality and concentration. Increasing the concentration reduces the overall size of the molecule by screening the excluded volume effects which increase the apparent stiffness of the backbone. In this study we map out the size of a bottlebrush polymer as a function of concentration for a single backbone length. Small-angle neutron scattering (SANS) measurements are conducted on a polynorbornene-based bottlebrush with polystyrene sidechains in a good solvent. The data are fit using a model which provides both the long and short axis radius of gyration (Rg,2 and Rg,1, respectively), providing a measure for how the conformation changes as a function of concentration. At low concentrations a highly anisotropic structure is observed (Rg,2/Rg,1 ≈ 4), becoming more isotropic at higher concentrations (Rg,2/Rg,1 ≈ 1.5). In a semi- dilute regime Rg,2 scales with the volume fraction (ϕ)-1/8, consistent with linear chains and star polymers. At higher concentrations the reduction in Rg,2 occurs much more quickly, with Rg,2 ≈ ϕ-0.58, a much stronger scaling than anticipated. Coarse-grained molecular dynamics simulations were also conducted to probe this behavior, both in implicit and explicit solvent. Both cases agreed with the general trend observed in the experimental results, but the simulations in the explicit solvent deviated from the implicit case at low concentrations. This demonstrates that hydrodynamic effects not captured in the implicit simulations are important and need to be considered in the dilute regime.

Citation

Macromolecules

Pub Type

Journals

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Citation

Sunday, D. , Chremos, A. , Martin, T. , Chang, A. , Burns, A. and Grubbs, R. (2020), The Concentration Dependence of the Size and Symmetry of a Bottlebrush Polymer in a Good Solvent, Macromolecules, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=929876 (Accessed April 26, 2024)