title: Synergistic Effects of Bound Micelles and Temperature on the Flexibility of Thermoresponsive Polymer Brushes.
abstract: The persistence length is a key parameter for the quantitative interpretation of the flexibility of polymers. We have studied complexes composed of a spherical poly(N-isopropylacrylamide) (PNIPAM) brush and a sodium dodecyl sulfate micelle in an effort to characterize the flexibility of tethered PNIPAM below the lower critical solution temperature TLCST. An analytical mean-field model is used to describe the persistence length Lpin a broad range of ψ, the number of bound micelles per chain. The persistence length of micelle-constrained PNIPAM is quantitatively correlated with the thermal energy kBT, electrostatic repulsion fC, and effective excluded-volume parameter νeff. The persistence length per ψ, which depends on T and fC, is found to scale with a synergistic effect fC/(ψkBT). The results reveal that the bound-micelle charges affecting the persistence length are analogous to the fixed charges of polyelectrolytes, though the bound micelles are separated by a large number of neutral monomers. The extension ⟨L⟩ of micelle-constrained PNIPAM decreases as ⟨L⟩ ∼ fC-βFwith fC, where βF≈ 0.58-0.8 depending on ψ, but as the universal power law ⟨L⟩ ∼ (fC/kBT)-0.6with the synergistic effect fC/(kBT), irrespective of ψ. In spite of the intricate interplay among the multiple components in the system, the extension scales as a function of νeffas ⟨L⟩ ∼ (νeff/ψLp)-βV, where βV≈ 0.35 for the significant monomer interaction and βV≈ 0.2 for the weak or negligible monomer interaction.
authors.affiliation: Department of Materials Science and Engineering and ‡Department of Chemical Engineering, Monash University , Clayton, VIC 3800, Australia.
authors.forename: Peng-Wei
authors.initials: PW
authors.lastname: Zhu
authors.affiliation: Department of Materials Science and Engineering and ‡Department of Chemical Engineering, Monash University , Clayton, VIC 3800, Australia.
authors.forename: Luguang
authors.initials: L
authors.lastname: Chen