使用X-Ray Photon Correlation Spectroscopy方法模擬奈米尺度粒子系統的動力學

Abstract

第一章主要說明X-Ray Photon Correlation Spectroscopy (XPCS)的重要性，XPCS為一種利用X射線研究物質動力學的技術，相較於另外一種利用可見光的技術Dynamic Light Scattering (DLS)因為X射線波長較短，使其可以探測更小的運動距離，因而非常適合研究奈米尺度下奈米顆粒的動力學行為。第二章中則是介紹XPCS理論的核心，藉由XPCS的方法可以獲得奈米顆粒的時間和空間相關性資料，而同調光源的高同調性質會使得相關性測量的準確性和靈敏性有極大的提升，使得光束照射在奈米顆粒時，可以獲得較好的繞射圖案。藉由分析繞射圖案，我們可以得知奈米粒子在溶液中的動力學狀態。因此XPCS為一個好的間接方法可以直接由奈米粒子的散射圖案來推論奈米粒子的實際運動狀況。第三章主要是介紹XPCS在本論文用到的模擬方法。我們分別給出數值計算的一些方法。藉由這些方法，來模擬我們在本論文的所有數據結果並分析，第四章則是主要著重在分析我們的模擬結果和討論我們的發現。藉由speckle pattern所計算出的times-correlation function的結果模擬結果，我們發現奈米物質在溫度範圍283K~343K的運動狀態且wave scattering vector 小於 2×10^7 m-1 時，膠體粒子的運動狀態為平衡狀態。第五章是根據以上的結果，經過分析和整理而得出最後結論，奈米粒子在這些溫度範圍內都滿足愛因斯坦-史塔克關係，代表奈米粒子在此溫度範圍滿足隨機運動。另一有趣發現則是奈米粒子在此溫度範圍內也都滿足常見的奈米系統的應力鬆弛模型，鬆弛模型係數γ 介於0.87 ~ 1.06之間。

Chapter 1 primarily discusses the importance of X-Ray Photon Correlation Spectroscopy (XPCS). XPCS is a technique that utilizes X-rays to study the dynamics of materials. Compared to Dynamics Light Scattering (DLS), which uses visible light, XPCS is particularly suitable for investigating the dynamics of nanoparticles at the nanoscale due to the shorter wavelength of X-rays, allowing for the detection of smaller movement distances. Chapter 2 introduces the core theory of XPCS. By employing XPCS, one can obtain time and spatial correlation information about nanoparticles. The high coherence of the coherent light source greatly enhances the accuracy and sensitivity of correlation measurements, resulting in improved diffraction patterns when the beam illuminates the nanoparticles. Analyzing these diffraction patterns allows us to infer the actual motion of the nanoparticles in solution. Thus, XPCS serves as an indirect method to deduce the real-time movement of nanoparticles based on their scattering patterns. Chapter 3 mainly describes the simulation methods used in this thesis. We provide various numerical calculation methods to simulate and analyze all the data results in our study. Chapter 4 focuses on analyzing our simulation results and discussing our findings. Through the time-correlation function obtained from the speckle pattern, we discovered that when the temperature ranged from 283K to 343K and the wave scattering vector was less than 2×10^7 m-1, the motion of colloidal particles reached an equilibrium state. Chapter 5 draws the final conclusions based on the above results, analysis, and organization. We found that within these temperature ranges, the nanoparticles satisfy the Einstein-Stokes relationship, indicating random motion. Another interesting finding is that the nanoparticles also adhere to the stress relaxation model commonly observed in nano systems, with the relaxation coefficient γ ranging from 0.87 to 1.06.