Tailored Composite Polymer-Metal Nanoparticles by Miniemulsion Polymerization and Thiol-ene Functionalization

Abstract

A simple and modular synthetic approach, based on miniemulsion polymerization, has been developed for the fabrication of composite polymer-metal nanoparticle materials. The procedure produces well-defined composite structures consisting of gold, silver or MnFe(2)O(4) nanoparticles (∼10 nm in diameter) encapsulated within larger spherical nanoparticles of poly(divinylbenzene) (∼100 nm in diameter). This methodology readily permits the incorporation of multiple metal domains into a single polymeric particle, while still preserving the useful optical and magnetic properties of the metal nanoparticles. The morphology of the composite particles is retained upon increasing the inorganic content, and also upon redispersion in organic solvents. Finally, the ability to tailor the surface chemistry of the composite nanoparticles and incorporate steric stabilizing groups using simple thiol-ene chemistry is demonstrated.

Figure 1

Schematic description of composite nanoparticle synthesis: (A) polystyrene-grafted gold nanoparticles are dispersed in monomer (divinylbenzene) and emulsified with aqueous surfactant solution (B) to form small, uniform monomer droplets (C), which are then polymerized to yield composite polymer-gold nanoparticles (D); hydrophilic polymer chains (poly(ethylene glycol)) are grafted to the surface of composite nanoparticles by thiol-ene chemistry (E).

Figure 2

Representative transmission electron micrograph from synthesis of composite polymer-gold nanoparticles using oleylamine-stabilized gold nanoparticles. Inset at top right shows both gold nanoparticle aggregation and incomplete encapsulation by polymer.

Figure 3

Representative transmission electron micrograph of composite polymer-gold nanoparticles, showing 13 nm gold nanoparticles (black domains) encapsulated within larger, spherical poly(divinylbenzene) nanoparticles (gray domains). Inset at top left shows enlarged image of a single composite particle.

Figure 4

Histogram showing the relative populations of composite nanoparticles containing different numbers of encapsulated 13 nm gold nanoparticles (compiled from TEM analysis of several hundred composite nanoparticles).

Figure 5

Change in the relative UV-visible absorbance maximum after exposure to excess potassium cyanide for citrate-stabilized gold nanoparticles (——●——; 10 equiv. of cyanide; λ_max = 520 nm) and composite polymer-gold nanoparticles (— –■– —; 100 equiv. of cyanide; λ_max = 550 nm) in water, and for composite nanoparticles in 50/50 THF/water (- - ♦ - -; 100 equiv. of cyanide; λ_max = 550 nm)

Figure 6

Thermogravimetric analysis (TGA) of pure poly(divinylbenzene) particles (————), and composite poly(divinylbenzene)-gold nanoparticles with predicted gold loadings of approximately 12 wt% (— — —), 23 wt% (—● — ●) and 33 wt% (● ● ● ●).

Figure 7

Transmission electron micrographs of composite polymer-gold nanoparticles prepared with gold content of (a) 23 wt%, and (b) 33 wt%.

Figure 8

Transmission electron micrographs illustrating the effect on composite nanoparticle formation of decreasing the CTAB surfactant concentration to (a) 0.57 mM, and (b) 0.17 mM.

Figure 9

Transmission electron micrographs illustrating the effect on composite nanoparticle formation of increasing the CTAB surfactant concentration to 17 mM, both before (a) and after (b) centrifugation to remove empty polymeric nanoparticles.

Figure 10

Photographs of purified composite nanoparticles redispersed in THF and left to stand for 24 hours (left), and following attachment of PEG surface groups by thiol-ene chemistry, redispersion in THF and left to stand for 24 hours (right).

Figure 11

Transmission electron micrographs of composite nanoparticles after redispersion in tetrahydrofuran (a), and after thiol-ene attachment of PEG and redispersion in chloroform (b).

Figure 12

Transmission electron micrograph of composite polymer-MnFe₂O₄ nanoparticles (a), hybrid polymer-gold-MnFe₂O₄ nanoparticles (b), composite polymer-silver nanoparticles (c), and composite polymer-gold nanorods (d).