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?

Mansfield E.D.H. Filippov S.K. de la Rosa V.R. Cook M.T. Grillo I. Hoogenboom R. Williams A.C. Khutoryanskiy V.V.
15 May 2021 Academic Press Inc.

Journal of Colloid and Interface Science
2021 #590 249 - 259 pp.

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 (5000 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.

Aggregation , PNIPAM , Poly(2-oxazoline) , SANS , Silica nanoparticles , Temperature-responsive polymers

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School of Pharmacy, University of Reading, Whiteknights, Reading, RG6 6AD, Berkshire, United Kingdom
Pharmaceutical Sciences Laboratory, Faculty of Science and Engineering, Åbo Akademi University, Turku, 20520, Finland
Department of Chemistry and Chemical Technology, Al-Farabi Kazakh National University, Almaty, 050040, Kazakhstan
Supramolecular Chemistry Group, Centre of Macromolecular Chemistry (CMaC), Department of Organic and Macromolecular Chemistry, Ghent University, Krijgslaan 281 S4, Ghent, B-9000, Belgium
Research Centre in Topical Drug Delivery and Toxicology, Department of Pharmacy, Pharmacology and Postgraduate Medicine, University of Hertfordshire, Hatfield, AL10 9AB, Hertfordshire, United Kingdom
Institut Laue-Langevin, 71 avenue des Martyrs, Grenoble, 38042, France

School of Pharmacy
Pharmaceutical Sciences Laboratory
Department of Chemistry and Chemical Technology
Supramolecular Chemistry Group
Research Centre in Topical Drug Delivery and Toxicology
Institut Laue-Langevin

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