Relaxation Dynamics of Nanoparticle-Tethered Polymer Chains

Sung A Kim, Rahul Mangal, Lynden A. Archer

Research output: Contribution to journalArticlepeer-review

79 Scopus citations

Abstract

© 2015 American Chemical Society. Relaxation dynamics of nanoparticle-tethered cis-1,4-polyisoprene (PI) are investigated using dielectric spectroscopy and rheometry. A model system composed of polymer chains densely grafted to spherical SiO2 nanoparticles to form self-suspended suspensions facilitates detailed studies of slow global chain and fast segmental mode dynamics under surface and geometrical confinement-from experiments performed in bulk materials. We report that unentangled polymer molecules tethered to nanoparticles relax far more slowly than their tethered entangled counterparts. Specifically, at fixed grafting density we find, counterintuitively, that increasing the tethered polymer molecular weight up to values close to the entanglement molecular weight speeds up chain relaxation dynamics. Decreasing the polymer grafting density for a fixed molecular weight has the opposite effect: it dramatically slows down chain relaxation, increases interchain coupling, and leads to a transition in rheological response from simple fluid behavior to viscoelastic fluid behavior for tethered PI chains that are unentangled by conventional measures. Increasing the measurement temperature produces an even stronger elastic response and speeds up molecular relaxation at a rate that decreases with grafting density and molecular weight. These observations are discussed in terms of chain confinement driven by crowding between particles and by the existence of an entropic attractive force produced by the space-filling constraint on individual chains in a self-suspended material. Our results indicate that the entropic force between densely grafted polymer molecules couples motions of individual chains in an analogous manner to reversible cross-links in associating polymers.
Original languageEnglish (US)
Pages (from-to)6280-6293
Number of pages14
JournalMacromolecules
Volume48
Issue number17
DOIs
StatePublished - Aug 17 2015
Externally publishedYes

Bibliographical note

KAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): KUS-C1-018-02
Acknowledgements: This work was supported by the National Science Foundation Award No. DMR-1006323 and by Award No. KUS-C1-018-02 made by King Abdullah University of Science and Technology (KAUST). Facilities available though the Cornell Center for Materials Research (CCMR) were used for this study (DMR-1120296). Use of the Advanced Photon Source, operated by the Argonne National Laboratory, was supported by the US DOE under Contract No. DE–AC02–06CH11357.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.

Fingerprint

Dive into the research topics of 'Relaxation Dynamics of Nanoparticle-Tethered Polymer Chains'. Together they form a unique fingerprint.

Cite this