Softening of the stiffness of bottlebrush polymers by mutual interaction

TL;DR

This study investigates how mutual interactions in bottlebrush polymers in a good solvent lead to a significant reduction in their stiffness, with experimental data supporting a concentration-dependent softening effect.

Contribution

It provides the first detailed experimental analysis of the concentration-dependent softening of bottlebrush polymers using multiple scattering techniques.

Findings

Persistence length decreases from 17.5 nm to 5 nm with increasing concentration.

Mutual interactions cause a measurable softening of the polymer chains.

Results align with theoretical predictions for polyelectrolyte chain behavior.

Abstract

We study bottlebrush macromolecules in a good solvent by small-angle neutron scattering (SANS), static light scattering (SLS), and dynamic light scattering (DLS). These polymers consist of a linear backbone to which long side chains are chemically grafted. The backbone contains about 1600 monomer units (weight average) and every second monomer unit carries side-chains with ca. 60 monomer units. The SLS- and SANS data extrapolated to infinite dilution lead to the form factor of the polymer that can be described in terms of a worm-like chain with a contour length of 380 nm and a persistence length of 17.5 nm. An analysis of the DLS data confirm these model parameters. The scattering intensities taken at finite concentration can be modeled using the polymer reference interaction site model. It reveals a softening of the bottlebrush polymers caused by their mutual interaction. We demonstrate that the persistence decreases from 17.5 nm down to 5 nm upon increasing the concentration from dilute solution to the highest concentration 40.59 g/l under consideration. The observed softening of the chains is comparable to the theoretically predicted decrease of the electrostatic persistence length of linear polyelectrolyte chains at finite concentrations.