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Materials 2018, 11(9), 1654; https://doi.org/10.3390/ma11091654

Thermoresponsive Core-Shell Nanoparticles: Does Core Size Matter?

University of Natural Resources and Life Sciences Vienna, Muthgasse 11, 1190 Vienna, Austria
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Received: 29 July 2018 / Revised: 28 August 2018 / Accepted: 3 September 2018 / Published: 7 September 2018
(This article belongs to the Special Issue Temperature-Responsive Polymers)
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Abstract

Nanoparticles grafted with a dense brush of hydrophilic polymers exhibit high colloidal stability. However, reversible aggregation can be triggered by an increase in temperature if the polymer is thermoresponsive, as the polymer shell partly loses its hydration. We investigate the role of nanoparticle curvature on the critical solution temperature (CST) of grafted poly(2-isopropyl-2-oxazoline) (PiPOx) and critical flocculation temperature (CFT) of the core-shell nanoparticle dispersion. Cores with diameters ranging from 5 to 21 nm were studied by temperature-cycled dynamic light scattering and differential scanning calorimetry over a large range of concentrations. We show that core size and curvature only have a minor influence on particle aggregation (CFT and cluster size), while they have major influence on the CST of the polymer shell. The densely grafted shells exhibit three distinct solvation transitions, the relative contributions of each is controlled by the core curvature. We link these transitions to different polymer density regimes within the spherical brush and demonstrate that the CST of the innermost part of the brush coincides with the CFT of the particle dispersion. View Full-Text
Keywords: poly(2-isopropyl-2-oxazoline) (PiPOx); lower critical solution temperature (LCST); critical flocculation temperature (CFT); superparamagnetic iron oxide nanoparticles (SPION); thermoresponsive polymer; reversible nanoparticle aggregation; spherical polymer brush shell; dynamic scanning calorimetry (DSC); dynamic light scattering (DLS); size and curvature dependence; core-shell nanoparticle poly(2-isopropyl-2-oxazoline) (PiPOx); lower critical solution temperature (LCST); critical flocculation temperature (CFT); superparamagnetic iron oxide nanoparticles (SPION); thermoresponsive polymer; reversible nanoparticle aggregation; spherical polymer brush shell; dynamic scanning calorimetry (DSC); dynamic light scattering (DLS); size and curvature dependence; core-shell nanoparticle
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Schroffenegger, M.; Reimhult, E. Thermoresponsive Core-Shell Nanoparticles: Does Core Size Matter? Materials 2018, 11, 1654.

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