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Control of dispersion-aggregation of nanoparticles by illumination

通过照明控制纳米颗粒的分散聚集

基本信息

批准号：
06453058
负责人：
KIMURA Keisaku
金额：
$ 3.84万
依托单位：
Himeji Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1995
项目状态：
已结题

项目摘要

Gold nanometer-sized particles were prepared by the gas flow-solution trap method. The dispersing solvent is 2-propanol and average size of starting particles is 8nm. On irradiation of an Ar-ion laser, the color of dispersion has changed from wine red to dark blue otherwise wine red for more than years. It was shown that dispersed particles agglomerated into fractal cluster in concurrent with the spectral change of increase in 750 nm band and decrease in 523nm plasmon band.The change of dispersion by the illumination of light resembles to the effect of the addition of salt. The stability of dispersion is most sensitive to the concentration of electrolyte in the dispersion because ions affect the Debye length around the particle sphere. Sudden coagulation started at the instant of addition of NaCl solution. That is, the initial peak maximum at 520 nm shifted toward red wavelength region upon increasing concentration of salt. This tendency is similar to the photocoagulation.Following the standard theory of colloids, the stability of sols is governed by balancing between van der Waals attraction and Coulombic repulsion of charged particles. It is obvious that the coagulation proceeds with the visible light energy. At Mie resonance frequency, the free electron-system in a metallic particle feels forced vibration at the resonance frequency causing large dipole oscillation. This large oscillation induced interparticle attractive force among the same particle likewise in the normal van der Waals force. As a result, the interaction is a function of the square of size of particles and the power of a field. The interaction energy has its maximum at about 20 nm and gradually decay for a larger size. Hence the system has to be a mesoscopic scale for a large enhancement to be observed.

采用气流-溶液捕集法制备了金纳米粒子。分散溶剂为异丙醇，起始颗粒的平均粒径为8 nm。经氩离子激光照射，分散体的颜色由酒红色变为深蓝色，或酒红色，时间超过几年。结果表明，分散粒子在750 nm波段的光谱变化和523 nm等离子体激元波段的光谱变化的同时，聚集成分形团簇，光照射下分散度的变化类似于盐的作用。分散液的稳定性对分散液中电解质的浓度最敏感，因为离子影响颗粒球周围的德拜长度。在加入NaCl溶液的瞬间开始突然凝固。也就是说，随着盐浓度的增加，520 nm处的初始峰最大值向红色波长区域移动。根据胶体的标准理论，溶胶的稳定性是由带电粒子的货车范德华吸引力和库仑排斥力的平衡决定的。很明显，凝聚是在可见光能量的作用下进行的。在米氏共振频率下，金属粒子中的自由电子系统感受到共振频率下的受迫振动，导致大的偶极振荡。这种大的振荡在相同的颗粒之间同样在正常的货车范德华力中引起颗粒间的吸引力。因此，相互作用是粒子尺寸平方和场功率的函数。相互作用能在约20 nm处达到最大值，并随着尺寸的增大而逐渐衰减。因此，系统必须是一个介观尺度的大增强被观察到。