Tuning the anisotropic heat release of individual gold nanorod-silica particles & The synthesis of Au-Silica Janus nanoparticles

• Main Authors: Li, Jheng-Ru, 李政儒
• Other Authors: Wang, Churng-Ren Chris
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/34597897866732544052

碩士 === 國立中正大學 === 化學暨生物化學研究所 === 101 === This thesis is composed of two subjects which are somewhat linked together. The part I is to tune the anisotropic heat release within individual gold nanorod-silica particles relies on the success in the non-uniform silica coating onto the gold nanorod surface with negligible thickness at the long-axis ends. We presented systematic studies in the dependence of the laser-induced isotropic/anisotropic heat release on several issues, such as the wavelength and the power of the laser light for either longitudinal or transverse surface plasmon resonances, the short-axis thickness and the porosities of the silica. The core-shell nanoparticles irradiated by a single laser pulse undergo a laser-induced shape transformation, or melting. Evidently, anisotropic heat release causes a rod-to-two spheres transformation, that we call the “split-melting”. On the other hand, a rod-to-single shorter rod, or single sphere, transformation is resulted from the isotropic heat release. It is called the “melting”, which is a thermodynamically favored process. Our experiments confirmed that the non-uniform silica coating acts as the critical role for the anisotropic heat release. Also, the directionality of the heat release does not depdend on the surface plasmon excitation mode. The maximum split-melting ratios observed in the non-uniform silica shell series reached ca. 89% in the 1064 nm and 2.5 W laser irradiation, and ca. 80 % in the case of the 532 nm and 3 W. The maximum melting ratios for the uniform silica shell series reached ca. 100% in the 1064 nm and 3 W laser irradiation, and ca. 94% in the case of the 532 nm and 3 W. In addition, from the studies of the laser-induced shape transformation of the non-uniform silica cases with negligible thickness at the long-axis ends we concluded that (i) decrease the short-axis silica thickness caused a decrease in the split-melting ratios, and (ii) the minimum value for the short-axis silica thickness which turns of the split-melting is ca. 9 nm. Meanwhile, the anisotropic heat release, or the split-melting ratio, can be greatly turned off by controlling the silica coating process to get a silica shell with higher porosity. The part II is to propose a novel method for the synthesis of Au-Silica Janus nanoparticles. The final products can be a few interesting nanostructures. The targeted Au-Silica Janus nanoparticles contain both gold and silica nanoparticles which are attached together. The underline approach for their synthesis is of using the gold nanorod-silica core-shell (AuNR@nu-silica) particles as the starting material and fine-tuning two competitive chemical processes occur simultaneously in a one-pot synthesis. Such two processes leading to our Janus nanoparticles are (i) the gold surface catalyzed gold particle growth at the longitudinal end of gold nanorod and (ii) the selective etching reactions on gold nanorod. The above-mentioned fine-tuning means adjusting experimental condition carefully to assure the etching reaction rate becomes slower than the surface-catalyzed growth rate. To achieve such goal, an additional effort was made in differentiating the “coating thickness” at the longitudinal ends of the AuNR@nu-silica starting nanostructure. This additional effort assures that the etching reaction and the surface-catalyzed gold growth process occur at different AuNR ends. Accordingly, the experimental conditions can be carefully adjusted to obtain several different nanostructures, which identify this synthetic scheme a versatile one for future challenge in the nanosynthesis. Keywords : anisotropic heat release, Au-Silica Janus nanoparticles, split-melting