Synthesis, Assembly And The Template Function Of Metal Nanoparticle-Coated Colloidal Microspheres

With the development of modern science and technology, the preparation andcharacterization of metal nanoparticles have been an active area of investigationbecause of their unique electronic and optical properties. Due to their properties aresubstantially distinct from those both the bulk phase and individual molecules, thesenanoparticles would be potentially applied in biological labeling, surface-enhancedRoman, solar cell, electrochromic devices, electroluminescent films, nonlinearoptical switches and high–density information storage systems. As an important part,colloidal particles coated or deposited with functional metal nanoparticles haveattracted more and more attentions in the modern material science. Thanks to manyyears of continuous efforts, a variety of simple and effective methods have beendeveloped to fabricate metal nanoparticle-coated colloidal microspheres andcore-shell microspheres, which undoubtedly drives the further extension of themethods for preparing the metal nanoparticle-caoted colloidal microsphers. On theother hand, the patterns and microengineering at the micro-and nano-scale have beenstill a center to the modern microelectronics and optoelectronics, and provided a lotof chances in the studies at microscopic chemistry, physics and biology. Methodsbased on the desired and controllable masks and templates for fabricating versatilepatterns have been more flexible and practiced among all methods for achievingordered arrays and patterns on the desirable surfaces. In addition, the development oflithography and nanosphere lithography techniques have greatly improved themethods for the desired arrays and patterns of the metal nanoparticels, and theircorresponding applications in the broad fields will drive the further extension andintersect between the sciences of chemistry, physics, biology, communication andelectron and so on.In Chapter Two, we synthesized the Ag nanoparticle-coated silica microspheresusing chemical reduction method. Through adjusting the time of washing bycentrifugation/redispersion method, we can easily tune the coating density of the Agnanoparticles. Using the Ag nanoparticle-coated silica microspheres as seeds, we canfabricate the Ag nanopartice-coated silica-PMMA core-shell microspheres throughcombining using sol-gel, grafting double bonds and emulsion polymerizationmethods. Etching away the silica microspheres, we can obtain the composite hollowcapsules with Ag nanoparticles in the interior surfaces. These core-shell and hollowmicrospheres with functional metal nanoparticles not only enriched the methods offabricating the functional colloidal microspheres, but also will benefit theconstruction of other nanoparticle-coated colloidal microspheres and functionalordered structures.In Chapter Three, using the Tollens-soaked stable silica colloidal crystals astemplate, we synthesized the Ag nanoparticle-coated silica colloidal crystals.Compared with the traditional methods, our method has several advantages such assimplicity, low cost and environmentally benign. At the same time , the Agnanoparticles are mainly distributed on the silica microspheres instead of in the voidsof the colloidal crystals. Due to the ordered structure of the colloidal crystals and theuniformity of the Ag nanoparticles, the composite colloidal crystals can be used asSERS and larger enhancement ability was observed. The Ag nanoparticle-coatedsilica colloidal crystals also can be further used as template to construct the orderedpolymer macroporous films with Ag nanoparticles in the inner pores. Because of thedistinct structure of the composite colloidal crystals and the ordered macroporousfilm, they not only can be potentially used in SERS, catalysis and microtemplate, butalso provide a platform for the fabrication of other nanoparticle-coated colloidalcrystals.In Chapter Four, using the modified "lift-up" soft lithography and chemicalreduction methods, we prepared monolayer ordered silica microspheresunsymmetrically coated with Ag nanoparticles in large area. Through microcontactprinting method, these unsymmetrical microspheres can be transferred onto asubstrate spin-coated with a thin layer of polymer film. At the same time, we alsorealize the transformation of the tropism of these microspheres. By etching away thesilica microspheres, we obtained Ag nanoparticle-doped ordered polymer voids.Combined using the pattern PDMS stamp and "lift-up" and chemical reductionmethods, we can obtain pattern monolayer ordered microspheres unsymmetricallycoated Ag nanoparticles in large area. Through one or two time microcontact printingprocedure at the later stage, we can obtain simple or complex pattern polymer voids.Through physical vapor deposition method, the monolayer silica microspheresobtained by using the developed "lift-up" soft lithography method can be directlyused as template to construct ordered hollow Pt half-spheres in large area. At thesame time, the Ag nanoparticle-coated monolayer ordered silica microspheres can beused as template to fabricate ordered hollow Pt half-spheres with Ag nanoparticles intheir interior surfaces. We further extended this method to the ordered silicamicrospheres unsymmetrically coated with Ag nanoparticles which have beentransferred onto the polymer spin-coated substrate. The methods mentioned abovenot only extended the synthesis and application of the functional microspheres andthe nanoparticle-coated microspheres, but also obtained some ordered metal patternswhich may display their charming properties in nanofabrication, micro-nano scalereaction vessel, photoelectronic, catalysis, crystals growth and surface science area.In summary, we developed some methods of preparing and patterning colloidalmicrospheres functionalized with metal nanoparticles. These patterned colloidalmicrospheres also can be used to construct other pattern metal surface. On the onehand, these methods extended the preparation and application of the functionalcolloidal particles;on the other hand, these pattern metal nanoparticles and films willfurther extend the application of the metal nanoparticles and semiconductornanocrystals, and also drive the development of micro-process.