Relaxation Processes in Supramolecular Metallogels Based on Histidine-Nickel Coordination Bonds

Shengchang Tang, Bradley D. Olsen

Research output: Contribution to journalArticlepeer-review

Abstract

Understanding the quantitative relationship between the dynamic mechanical properties of associating polymer networks and the dynamics of sticker bonds represents an important problem in polymer science because materials mechanics is affected by not only the sticker bond chemistry but also the sticker position, the polymer structure, and the physical environment of the associating polymers such as concentration and solvent quality. In this study, associating networks formed by structurally well-defined linear poly(N,N-dimethylacrylamide) polymers with histidine side groups in complexation with Ni2+ ions are chosen as a model system. "Sticker diffusion and dissociation spectrometry" is developed as a new method to quantify the dissociation dynamics of stickers within the network environment where the stickers are covalently attached to polymers above their overlap concentration. The estimated time constants for junction dissociation in gels are shown to be substantially different than the ones measured by metal exchange experiments on small-molecule junctions in the dilute solution limit. Additionally, the in-gel dissociation time constants exhibit the same temperature dependence as the network relaxation times inferred from rheological characterization, which serves as the basis for time-temperature superposition, provided that the network relaxation is governed by the dissociation kinetics of stickers. Furthermore, self-diffusion of these associating polymers is probed by forced Rayleigh scattering, and pure Fickian diffusive behavior is revealed. The characteristic time constants for all the explored dynamic processes are finally viewed in the superimposed frequency sweep spectrum, demonstrating the inherent hierarchical relaxation in associating polymer networks even with only a single type of junction functionality.

Original languageEnglish (US)
Pages (from-to)9163-9175
Number of pages13
JournalMacromolecules
Volume49
Issue number23
DOIs
StatePublished - Dec 13 2016

ASJC Scopus subject areas

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry

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