Synthesis And Self-assembles Of Gold Nano-Materials With The Surfactants

Among many kinds of nanomaterials, gold nanomaterials have attracted wide attentions and have been studied extensively. There are many unique optical, electrical, and magnetostatic properties for the gold nanomaterials. Furthermore, due to the good properties biocompatibility and chemical stability, gold nanomaterials are also the noticeable research system in the biomedicine and biochemical detection.In the past decade, there has been tremendous progress in the shape-controlled synthesis of gold nanocrystals. In particular, a variety of colloidal chemical methods have been developed to fabricate and assemble gold nanocrystals, and there is a growing emphasis on these methods. In the synthesis and assemblies of gold nanocrystals by colloidal chemical methods, various surfactants have been widely employed as capping agents to exert exquisite control over the nucleation and growth of gold nanocrystals. In addition to the role of capping agents, surfactants which undergo strong interactions with gold, and can even form coordination complexes. All in all, a variety of surfactants with different headgroups, hydrophobic chains, counterions, and molecular architectures, have been used for the shape-controlled synthesis and assemblies of gold nanocrystals. Meanwhile, there are also many key points which are needed further investigation. In this thesis, we studied the preparation and assemblies of gold nanostructures with various shapes using surfactants as the capping agents. The thesis is divided into three sections, which are summarized as following:Section I, Gold nanostars and gold nanodendrites were readily synthesized by the reduction of HAuCl4 with ascorbic acid in aqueous mixed solutions of the cationic surfactant decane-1,10-bis(methylpyrrolidinium bromide) ([mpy-C10-mpy]Br2) and the anionic surfactant sodium dodecyl sulfonate (SDS). The interconversion of morphologies between gold nanostars and gold nanodendrites can be achieved by changing the reaction temperature under the otherwise identical conditions, which is seldom reported. Due to the electrostatic interaction, the introduction of SDS brought the dramatic impact to the formation process and the final morphologies of the gold nanostructures. Both of the hierarchical structures were found to yield large surface-enhanced Raman scattering (SERS) enhancement factors for rhodamine 6G (R6G) and the aspect ratio is a key factor for the enhancement.In section Ⅱ, Gold nanorods have been recognized as a good candidate for developing novel nanomaterials due to their exceptional optical properties. However, their assemblies, especially with the assisted ionic liquid, have not been well characterized. In this paper, we report the self-assembly of gold nanorods using thiol functionalized ionic liquid (1-methyl-3-(20-mercaptoacetoxyethyl) imidazolium bromine) (TFIL). We found that gold nanorods can self-assemble via two different ways:From end-to-end to side-by-side with the increase of TFIL concentration. The shift of the absorption peak in UV-vis spectrum indicates the change of the assembly fashion. We propose that the pep stacking interactions between the imidazole rings of TFIL molecules play the most important role in regulating the assembly process. The energy calculation further demonstrated that the face to face stacked orientation was the most stable geometry at high TFIL concentration, which supports the proposed mechanism.In section Ⅲ, Facile synthesis and 1D self-assembly of gold nanoparticles were achieved using a series of nonionic surfactants (Tween 20, Tween 40, and Tween 60). The assembly process can be controlled by adjusting the fine structures of surfactants. The effects of the molecular structures of capping agents were demonstrated and the formation mechanism based on the nonuniform distribution of capping ligands around gold nanoparticles was proposed. Systems with mixed capping agents (Tween 20 and Tween 60 or Triton X-100) were also investigated. Due to the different capping fashions of the mixed surfactants, the obtained gold nanostructures were changed from chains to particles. Besides, the diverse capping fashions canalso interpret the different stabilities of the nanostructures in the saline solutions.