Bottlebrush polymers in the melt and polyelectrolytes in solution share common structural features

Abstract

Uncharged bottlebrush polymer melts and highly charged polyelectrolytes in solution exhibit correlation peaks in scattering measurements and simulations. Given the striking superficial similarities of these scattering features, there may be a deeper structural interrelationship in these chemically different classes of materials. Correspondingly, we constructed a library of isotopically labeled bottlebrush molecules and measured the bottlebrush correlation peak position q*=2π/ξ by neutron scattering and in simulations. We find that the correlation length scales with the backbone concentration, ξ∼cBB−0.47, in striking accord with the scaling of ξ with polymer concentration cP in semidilute polyelectrolyte solutions (ξ∼cP−1/2). The bottlebrush correlation peak broadens with decreasing grafting density, similar to increasing salt concentration in polyelectrolyte solutions. ξ also scales with sidechain length to a power in the range of 0.35–0.44, suggesting that the sidechains are relatively collapsed in comparison to the bristlelike configurations often imagined for bottlebrush polymers.

Independently Tuning Elastomer Softness and Firmness by Incorporating Side Chain Mixtures into Bottlebrush Network Strands

“…29 Likewise, USAXS measurements of bulk LBL plastomers and B block melts show a consistent monomodal shift of a characteristic scattering peak around ≈ 1 −1 (Figure 3C), which is typically oversimplified as a backbone-backbone correlation or brush diameter. 28,[30][31][32] The resulting spacing = 2 ⁄ scales with 〈 〉 as ~ 〈 〉 0.41±0.01 (Figure 3D) and is consistent with recent small-angle neutron scattering ( ~0 .40±0.04 ), 32 computer simulations ( ~ 0.39±0.01 ), and theoretical studies (~3 /8 ). 33 The last highlights the complex physical origin of due to coupled density fluctuations from both backbone monomers and side chains constrained by melt incompressibility.…”

2020 NIST Center for Neutron Research accomplishments and opportunities

“…Similarly, within each bottlebrush chemistry, the bottlebrushes with longer sidechains display sharper correlation peaks. All of these trends in ξ are reproduced in structure factors calculated from coarse-grained molecular dynamics simulations from this study and previous ones [7][8][9].…”

“…This may be because the d 7 electron configuration of Co 2+ favors a weak Jahn-Teller distortion in octahedral coordination, which is unavailable in the hibonite structure. Neither the TBP nor tetrahedral environments require a Jahn-Teller distortion for d 7 , however, the tetrahedral site has a much higher percent of Co 2+ in refined compositions. This is attributed to the displacement of the metal center of the TBP away from the trigonal plane (Fig.…”

“…[2] BT-4 Filter Analyzer Neutron Spectrometer with cooled Be/Graphite filter analyzer for chemical spectroscopy and thermal triple axis spectrometer. [3] [4] [5] [6] [7] [8] [9] [10]…”

“…Despite this simple picture, bottlebrush studies still seek to further elucidate the relationship between the molecular design of the polymer and its conformation in order to create design rules that can be leveraged in the development of new bottlebrush-based materials. Here, we combine polymer synthesis, neutron characterization, and molecular simulation to show that backbones of uncharged bottlebrush polymers in bulk adopt similar conformational statistics to charged, linear chain polymers in solution [7].…”