Thermoresponsive Core-Shell Nanoparticles: Does Core Size Matter?

• Published in: Materials Vol. 11; no. 9; p. 1654
• Main Authors: Schroffenegger, Martina, Reimhult, Erik
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 07.09.2018; MDPI
• Subjects: Agglomeration; Brushes; Cellulose; Composite materials; core-shell nanoparticle; Core-shell particles; critical flocculation temperature (CFT); Curvature; Dopamine; dynamic light scattering (DLS); dynamic scanning calorimetry (DSC); Flocculation; Grafting; lower critical solution temperature (LCST); Molecular weight; Morphology; Nanoparticles; Photon correlation spectroscopy; poly(2-isopropyl-2-oxazoline) (PiPOx); Polymerization; Polymers; reversible nanoparticle aggregation; size and curvature dependence; Solvation; spherical polymer brush shell; superparamagnetic iron oxide nanoparticles (SPION); Surfactants; thermoresponsive polymer; Germany; critical flocculation temperature (CFT); dynamic light scattering (DLS); size and curvature dependence; lower critical solution temperature (LCST); thermoresponsive polymer; poly(2-isopropyl-2-oxazoline) (PiPOx); reversible nanoparticle aggregation; superparamagnetic iron oxide nanoparticles (SPION); core-shell nanoparticle; spherical polymer brush shell; dynamic scanning calorimetry (DSC)
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma11091654

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.