A Facile Synthesis of Asymmetric Hybrid Colloidal Particles

Abstract

This paper describes a simple approach to the synthesis of asymmetric, hybrid colloidal particles by precipitation polymerization. The key is to introduce Au or Ag colloids 2 min after (rather than before) starting the polymerization. The hybrid particles were uniform in size, and each one of them only contained one Au (or Ag) nanoparticle in its surface. Due to the simplicity of this procedure, it should be possible to use it for large-scale production. This method can be extended to metal nanoparticles other than Au and Ag and with a range of sizes, as long as they have appropriate charges on the surface. xia@biomed.wustl.edu. Increasing attention has been paid to colloidal particles with an asymmetric, hybrid structure because of their use in applications such as fabrication of optical, optoelectronic, and sensing devices through the "bottom up" approach. 1 Many efforts have been devoted to the synthesis of asymmetric, hybrid colloidal particles, and approaches include surface selective modification, 2 template-assisted self-assembly, 3 phase separation, 4 surface-controlled nucleation and growth, 5 and microfluidic techniques. 6 In spite of the success, it is worth pointing out that most of these methods cannot be easily applied to large-scale production because of the two-dimensional strategy or multiple steps involved in a typical fabrication process. Still, a facile and robust procedure is desired for the preparation of asymmetric, hybrid colloidal particles. NIH Public AccessHere we report a simple and versatile procedure for generating asymmetric, hybrid particles consisting of metal nanoparticles and polymer beads. We simply modified precipitation polymerization of polystyrene (PS) by adding Au (or Ag) colloids into the system after the polymerization had proceeded for a few minutes. The asymmetric particles were uniform in size and morphology, with each PS bead containing only one Au or Ag nanoparticle in its surface. Scheme 1 shows a schematic illustration of the procedure we used for generating the Au-PS asymmetric, hybrid particles. We firstly added styrene and divinylbenzene (DVB) to a mixture of ethanol and water, in which 4-styrenesulfonic acid sodium salt (NaSS) and potassium persulphate (KPS) had been dissolved. Since NaSS and KPS could stabilize the growing PS beads, we did not introduce other surfactants into the reaction system. After 2 min into the synthesis at 70 °C, we introduced Au colloids (50 nm in diameter) into the reaction mixture. At this point, PS oligomers and/or monomers started to nucleate by adsorbing onto the surface of Au nanoparticles, then grew in size, and eventually evolved into spheres as confined by surface tension. After 4 h into the reaction, the final product of hybrid particles was harvested by centrifugation and repeated washing with a mixture of ethanol and water. Figure 1 shows SEM and TEM images of the as-prepared Au-PS asymmetric, hybrid particles. The particles were slightly nonspherical in shape, but uniform in size with an average diameter of 300 n...

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