Pulsed field gradient NMR studies of polymer adsorption on colloidal CdSe quantum dots

Lei Shen, Ronald Soong, Mingfeng Wang, Anna Lee, Chi Wu, Gregory D. Scholes, Peter M. Macdonald, Mitchell A. Winnik

Research output: Contribution to journalArticlepeer-review

33 Scopus citations

Abstract

Pulsed field gradient nuclear magnetic resonance (PFG NMR) experiments have been used to examine ligand exchange between poly(2-(N,N-dimethylamino)ethyl methacrylate) (PDMA) (Mn = 12 000, Mw/Mn = 1.20, Nn = 78) and trioctylphosphine oxide (TOPO) bound to the surface of CdSe/TOPO quantum dots (QDs). We show that PFG 1H NMR can quantify the displacement of TOPO by PDMA through its ability to differentiate signals due to TOPO bound to the QDs versus those from TOPO molecules free in solution. For CdSe QDs with a band edge absorption maximum at 558 nm (diameter 2.7 nm by transmission electron microscopy), we determined that, at saturation, 8 polymer chains on average displace greater than 90% of the surface TOPO groups. At partial saturation, with an average of 6 polymer chains/QD, each TOPO displaced requires 28 DMA repeat units. Assuming that one Me2N- group binds to a surface Cd2+ for each TOPO displaced, we infer that only about 3% of the DMA units are directly bound to the surface. The remaining groups are present as loops or tails that protrude into the solvent and increase the hydrodynamic diameter of the particles.

Original languageEnglish (US)
Pages (from-to)1626-1633
Number of pages8
JournalJournal of Physical Chemistry B
Volume112
Issue number6
DOIs
StatePublished - Feb 14 2008

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

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