Reversible switching between hydrophilic and hydrophobic superparamagnetic iron oxide microspheres via one-step supramolecular dynamic dendronization: exploration of dynamic wettability

ACS Appl Mater Interfaces. 2009 Sep;1(9):2005-12. doi: 10.1021/am900367a.

Abstract

We describe the use of hydrophobic poly(aryl ether) dendrons to peripherally functionalize hydrophilic amine-containing superparamagnetic iron oxide microspheres (SPIO-NH2) in one step via imine formation. The reversible formation of imine bonds in the absence/presence of water renders dynamic control of the hydrophilicity and hydrophobicity of the microspheres (SPIO-Gn). The dynamic nature of the imine-containing dendronized microspheres (SPIO-Gn) can be "fixed" by locking the reversible 2,6-diiminopyridyl moieties with metal cations (Zn2+, Co2+, and Ni2+) to afford kinetically stable dendronized microspheres (SPIO-Gn-M). Isolation of these microspheres is facilitated by convenient magnetic separation by an externally applied magnetic field. Characterization of these novel organic-inorganic hybrid microspheres has been performed by various techniques using UV/visible absorption and Fourier transform infrared spectroscopies, transmission electron microscopy, thermogravimetric analysis, and a vibrating sample magnetometer. We have demonstrated the stability and reversible switching of hydrophilicity/hydrophobicity by contact-angle measurements. In particular, the hydrophilic SPIO-NH2 microspheres demonstrated a contact angle of 42 +/- 2 degrees when a drop of water was added to a SPIO-NH2-coated mica surface. On the other hand, the hydrophobic SPIO-Gn-M dendronized microspheres demonstrated a contact angle of 85 +/- 2 degrees , an observation that involves an increase of the contact angle of over 40 degrees . Furthermore, when a drop of water was placed on a dynamic SPIO-Gn-coated mica surface, the contact angle of the water droplet decreased in time. Comparatively, the rate of decrease of the contact angle is H2O > 1% Co(OAc)2/H2O > N,N'-dimethylformamide/H2O (1:1).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amines / chemistry
  • Chemistry / methods
  • Ferric Compounds / chemistry*
  • Hydrophobic and Hydrophilic Interactions
  • Imines / chemistry
  • Kinetics
  • Materials Testing
  • Microscopy, Electron, Transmission / methods
  • Microspheres*
  • Solvents / chemistry
  • Spectrophotometry, Ultraviolet / methods
  • Surface Properties
  • Wettability

Substances

  • Amines
  • Ferric Compounds
  • Imines
  • Solvents
  • ferric oxide