Geometrical Constraints of Poly(diethylene glycol methyl ether methacrylate) Brushes on Spherical Nanoparticles and Cylindrical Nanowires: Implications for Thermoresponsive Brushes on Nanoobjects

We report on the polymerization kinetics of thermoresponsive poly(diethylene glycol methyl ether methacrylate) (PDEGMA) brushes, which are used in novel cell release coating, on curved spherical silica nanoparticles (NPs with radii of 23 ± 5 nm, 70 ± 13 nm, and 148 ± 16 nm) and aligned cylindrical silicon nanowires (SiNWs with radii of 155 ± 10 nm and 391 ± 15 nm and a length of 3.75 ± 0.30 μm). The polymer brushes, which were synthesized by surface-initiated atom transfer radical polymerization (SI-ATRP) and additionally surface-initiated activator regenerated by electron transfer (SI-ARGET-ATRP) approaches, were analyzed by field emission scanning electron microscopy, contact angle measurements, spectroscopic ellipsometry, time-of-flight secondary ion mass spectrometry, gel permeation chromatography, and thermal gravimetric analysis. On spherical NPs it was found that with increasing NP size thinner PDEGMA brushes with higher grafting density and higher dispersities were obtained. The apparent kinetics of brush growth increased with decreasing NP size. Likewise, on SiNWs thinner PDEGMA brushes and slower kinetics were observed with increasing wire radius. For SI-ARGET-ATRP, the top regions between the SiNWs were completely filled with PDEGMA brushes; however, as confirmed by TGA, the overall occupied fractional volume of polymer in the wire-covered substrates was <50%, implying a tapered brush morphology on the SiNW sidewalls. An overall kinetic profiles demonstrated that the brush thickness and growth rates increased on both NPs and SiNWs with increasing curvature, which is attributed to increasingly relaxed chain confinement during brush growth. A better understanding of PDEGMA-brush functionalized curved interfaces will be beneficial for the development of optimized controllable thermoresponsive coatings on curved supports and nanomaterials, which can be expanded to the fields of drug delivery, cell studies, and beyond.