金奈米棒－二氧化矽核殼粒子非等向性熱釋放之調控暨金－二氧化矽雙面奈米粒子之合成

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

李政儒(Jheng-Ru Li)

指導教授 ： 王崇人

國立中正大學/理學院/化學暨生物化學系/碩士(2013年)

摘要

本研究分為兩部分。第一部分探討在單一奈米粒子內調節非等向性之熱釋放。第二部分則是開發一個新方法藉以合成金－二氧化矽雙面奈米粒子。在個別金奈米棒－二氧化矽奈米粒子內調節非等向性之熱釋放方面，主要倚賴長短軸不均勻包覆二氧化矽殼層所致，實驗操控短軸殼層厚度均為約11 nm，以及長軸厚度分別為0 nm（不均勻二氧化矽殼層）以及8 nm（均勻二氧化矽殼層）。在水溶液中以雷射誘發熱釋放，會因為金奈米棒長短軸所接觸之介質不同，分別為水及二氧化矽，而導致異向性之熱釋放。本論文有系統的探討不同激發模式與不同雷射強度對於熱釋放方向性可能之影響，以及透過調控殼層厚度或緻密度達到操控熱釋放方向性的可能性。研究採用兩種誘發雷射之波長（1064 nm及532 nm），造成金奈米棒長軸或短軸表面電漿共振之激發；同時不同的雷射光強度，輸出功率介於1 W至3 W。我們主要以雷射誘發奈米金棒形狀轉換的方式間接說明粒子內熱釋放之方向性；舉例來說，若轉換途徑為棒球，代表粒子內熱釋放為等向性。若轉換途徑裂熔（Split-melting）的方式，則代表粒子內熱釋放為非等向性。此一有趣現象文中會清楚陳述。實驗證實粒子形變的方式與二氧化矽殼層之均勻度有絕對之關係，與表面電漿激發模式無關。不均勻殼層粒子內之金奈米棒會行裂熔成兩顆球， 透過非等向性熱釋放造成裂熔的最高形變率可達約89 %（1064 nm; 2.5 W），以及約80%（532 nm; 3 W）。均勻殼層粒子內之金奈米棒會因較慢且等向性熱釋放，透過棒球形變之途逕縮熔為一顆球或短棒，其最高形變率可達約100%（1064 nm; 3 W），以及約94%（532 nm; 3 W）。另外，當長軸維持殼層厚度為零奈米，短軸二氧化矽殼層厚度變小會造成裂熔成兩顆球的形變率明顯降低。實驗同時得知，會因粒子內非等向性之熱釋放而造成裂熔的殼層厚度差值，最小須為9 nm。當不均勻二氧化矽殼層的緻密度在透過實驗仔細地操控後而得以降低時，說明裂熔成兩顆球的形變率亦會明顯下降。關於開發合成金－二氧化矽雙面奈米粒子的新方法部分，我們提出一項新穎的合成策略，主要在於利用上述之金奈米棒－不均勻二氧化矽核殼粒子為起始物，透過仔細滿足三項條件來達成此一目標：一、端點金表面催化奈米金粒子之成長，二、選擇反應速率比金成長慢的金侵蝕機制，以及三、金奈米棒長軸一端外露一端包覆的不均勻核殼結構。當侵蝕與成長反應同時進行，由於反應速率的差異，金離子先在長軸外露端進行表面催化成長，包覆端則因殼層阻礙無法進行。待還原試劑用盡，侵蝕反應成為主要步驟，由於兩端金原子不對稱分佈，長軸包覆端金會先被侵蝕殆盡，最終獲得一端為金一端為二氧化矽的雙面奈米粒子結構。
關鍵詞：奈米粒子非等向性熱釋放；金－二氧化矽雙面奈米粒子

關鍵字

金－二氧化矽雙面奈米粒子 ； 奈米粒子非等向性熱釋放

並列摘要

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

並列關鍵字

Au-Silica Janus nanoparticles ； anisotropic heat release ； split-melting

參考文獻

18. Wei, C.-W.; Poe, C.; Chen, C.-M.; Lee, Y.-H.; Wang, C.-R. C.; Li, P.-C., San Francisco, California, USA, Oraevsky, A. A.; Wang, L. V., Eds. SPIE: San Francisco, California, USA, 2010; pp 75641S-9.

14. Chang, S.-S.; Shih, C.-W.; Chen, C.-D.; Lai, W.-C.; Wang, C. R. C., Langmuir 1998, 15 (3), 701-709.

3. Chou, C.-H.; Chen, C.-D.; Wang, C. R. C., The Journal of Physical Chemistry B 2005, 109 (22), 11135-11138.

32. Perrault, S. D.; Chan, W. C. W., Journal of the American Chemical Society 2010, 132 (33), 11824-11824.

1. Murphy, C. J., Science 2002, 298 (5601), 2139-2141.