Understanding the temperature induced aggregation of silica nanoparticles decorated with temperature-responsive polymers: can a small step in the chemical structure make a giant leap for a phase transition?

Edward D.H. Mansfield, Sergey K. Filippov, Victor R. de la Rosa, Michael T. Cook, Isabelle Grillo, Richard Hoogenboom, Adrian C. Williams, Vitaliy V. Khutoryanskiy

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Abstract

Temperature-responsive nanomaterials have gained increasing interest over the past decade due their ability to undergo conformational changes in situ, in response to a change in temperature. One class of temperature-responsive polymers are those with lower critical solution temperature, which phase separate in aqueous solution above a critical temperature. When these temperature-responsive polymers are grafted to a solid nanoparticle, a change in their surface properties occurs above this critical temperature, from hydrophilic to more hydrophobic, giving them a propensity to aggregate. This study explores the temperature induced aggregation of silica nanoparticles functionalised with two isomeric temperature-responsive polymers with lower critical solution temperature (LCST) behavior, namely poly(N-isopropyl acrylamide) (PNIPAM), and poly(2-n-propyl-2-oxazoline) (PNPOZ) with similar molecular weights (5,000 Da) and grafting density. These nanoparticles exhibited striking differences in the temperature of aggregation, which is consistent with LCST of each polymer. Using a combination of small-angle neutron scattering (SANS) and dynamic light scattering (DLS), we probed subtle differences in the aggregation mechanism for PNIPAM- and PNPOZ-decorated silica nanoparticles. The nanoparticles decorated with PNIPAM and PNPOZ show similar aggregation mechanism that was independent of polymer structure, whereby aggregation starts by the formation of small aggregates. A further increase in temperature leads to interaction between these aggregates and results in full-scale aggregation and subsequent phase separation.
Original languageEnglish
Pages (from-to)249-259
Number of pages11
JournalJournal of Colloid and Interface Science
Volume590
Early online date27 Jan 2021
DOIs
Publication statusPublished - 15 May 2021

Keywords

  • Silica nanoparticles
  • Aggregation
  • SANS
  • temperature-responsive polymers
  • PNIPAM
  • poly(2-oxazoline)
  • Poly(2-oxazoline)
  • Temperature-responsive polymers

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