The Brownian dynamics （BD） simulation of a dilute surfactant solution is conducted in a steady shear flow. The rodlike micelle is assumed as a rigid rod composed of lined-up beads. A novel intercluster potential mod...The Brownian dynamics （BD） simulation of a dilute surfactant solution is conducted in a steady shear flow. The rodlike micelle is assumed as a rigid rod composed of lined-up beads. A novel intercluster potential model is introduced for describing the interactions between, micelles. In the model, the Lennard-Jones and the soft-sphere potentials are used as inter-bead potentials for end-end and interior-interior beads, respectively. The micelles are combined at their ends to form a network structure at lower shear rates and are disconnected to become more and more parallel to the shear flow direction with increasing shear rate. The change of micellar microstructures with the variation of the shear rate results in shear thinning characteristics of the computed shear viscosities and first normal stress difference coefficients. The effects of surfactant solution concentration on the micellar structures and rheological properties are also investigated. Results show that the shear viscosities and the first normal stress difference coefficients increase with increasing the viscosity of the surfactant solution.展开更多
The appropriate choice of chemical composition of a metallic precursor, which produces the basic structure units in the growth process of nanocrystals, is a high priority in the synthesis of metal--especially Au--nano...The appropriate choice of chemical composition of a metallic precursor, which produces the basic structure units in the growth process of nanocrystals, is a high priority in the synthesis of metal--especially Au--nanoparticles. In the present work, Au seeds （prepared by the reduction of Au3＋ solution with NaBI~ in the presence of cetyltrimethylammonium bromide （CTAB）） have been used to initiate the growth of Au nanoparticles from two different Au precursors. When an aqueous Au＋ solution prepared in the presence of CTAB micelles was treated with ascorbic acid in the presence of the gold seeds, a high yield （up to 92%） of gold nanoparticles was obtained. By varying the volume of the seed solution with a fixed amount of Au＋, we can effectively control the morphological transformation of the resulting Au nanoparticles from cubes to octahedra. When an aqueous Au3＋ solution was prepared in the presence of CTAB micelles and treated with ascorbic acid in the presence of the gold seeds, smaller yields of Au nanoparticles were obtained. A preliminary growth mechanism has been proposed based on the changes induced by varying the amount of ascorbic acid and the ratio of the concentration of Au＊ to the number of seeds.展开更多
文摘The Brownian dynamics （BD） simulation of a dilute surfactant solution is conducted in a steady shear flow. The rodlike micelle is assumed as a rigid rod composed of lined-up beads. A novel intercluster potential model is introduced for describing the interactions between, micelles. In the model, the Lennard-Jones and the soft-sphere potentials are used as inter-bead potentials for end-end and interior-interior beads, respectively. The micelles are combined at their ends to form a network structure at lower shear rates and are disconnected to become more and more parallel to the shear flow direction with increasing shear rate. The change of micellar microstructures with the variation of the shear rate results in shear thinning characteristics of the computed shear viscosities and first normal stress difference coefficients. The effects of surfactant solution concentration on the micellar structures and rheological properties are also investigated. Results show that the shear viscosities and the first normal stress difference coefficients increase with increasing the viscosity of the surfactant solution.
基金Acknowledgements This work was supported by National Basic Research Program of China （973 Program No. 2009CB930703） and National Natural Science Foundation of China （No. 21033007）. We thank Dr. Jiawei Yan, Yongli Zheng, and Haixin Lin for helpful discussion. We also thank Zhaobin Chen for ICP-AES measurements.
文摘The appropriate choice of chemical composition of a metallic precursor, which produces the basic structure units in the growth process of nanocrystals, is a high priority in the synthesis of metal--especially Au--nanoparticles. In the present work, Au seeds （prepared by the reduction of Au3＋ solution with NaBI~ in the presence of cetyltrimethylammonium bromide （CTAB）） have been used to initiate the growth of Au nanoparticles from two different Au precursors. When an aqueous Au＋ solution prepared in the presence of CTAB micelles was treated with ascorbic acid in the presence of the gold seeds, a high yield （up to 92%） of gold nanoparticles was obtained. By varying the volume of the seed solution with a fixed amount of Au＋, we can effectively control the morphological transformation of the resulting Au nanoparticles from cubes to octahedra. When an aqueous Au3＋ solution was prepared in the presence of CTAB micelles and treated with ascorbic acid in the presence of the gold seeds, smaller yields of Au nanoparticles were obtained. A preliminary growth mechanism has been proposed based on the changes induced by varying the amount of ascorbic acid and the ratio of the concentration of Au＊ to the number of seeds.
