動態表面光散射（surface laser light scattering，SLLS）是一種強而有力的非破壞性檢測技術，可用於探測液體/液體或氣體/液體等界面的熱激發現象，以得到該流體的界面特性，包括表面張力以及黏性等。本實驗的雷射光源經由繞射光柵分光，提供穩定的區域震盪源（local oscillator）與散射光，在樣品表面產生干涉。散射光的波向量可由光電倍增管（photomultiplier tube，PMT）前的針孔（pin hole）進行選擇，最後由傅立葉光譜分析儀（fast Fourier transform，FFT）得到該階（order）散射光之光譜。由於聚異丙基烯醯胺（PNIPAM）對周圍環境（例如溫度、pH值、溶劑組成等）變化十分明顯的有趣特性，因此成為我們研究的對象。在本論文中，嘗試改變溶劑的組成成分，實驗結果顯示，隨著甲醇相對於水的比例增加，溶液中是否含有聚異丙基丙烯醯胺，對界面的表面張力之影響似乎愈來愈小，表示濃度較純的甲醇有將聚異丙基丙烯醯胺吸往流體內部的趨勢。

Surface Laser Light Scattering (SLLS) is a heterodyne detection technique used to probe the surface properties of fluid interfaces. These interfaces are either liquid/liquid or vapor/liquid, and they may include insoluble monolayers or polymer films deposited on liquid surfaces as well as microemulsions in solution at low concentration. This technique provides one with a nonperturbative way to obtain surface tension and viscosity. A diffraction grating is employed to provide a stable local oscillatior, hence selecting an accurate ripplon wave vector . This thesis deals with the investigation of the interface between air and solution consisting of the methanol and water mixture and poly(N-isopropylacrylamide) or PNIPAM which is one of the fascinating polymeric materials. The polymer PNIPAM shows distinct responses to variations in the surrounding environment (such as thermal gradient, change in pH, etc.). The surface tension extracted from the SLLS data using the Kelvin equation is found to agree well with that obtained by using the Wilhelmy plate method. For the range of wave vectors cm-1, the power spectrum detected in frequency domain can be fit to a Lorentzian profile. Our experiments show that when the volume percentage of methanol increases, the interfacial property becomes insensitive to the presence of PNIPAM.

ACKNOWLEDGEMENTS i

ABSTRACT ii

LIST OF FIGURES v

Chapter 1. INTRODUCTION 1

Chapter 2. THEORY OF SURFACE WAVES 5
2.1 Navier-Stokes Equation 5
2.2 Constitutive Equation of Simple Surface 8
2.3 Equation of Motion and Boundary Conditions 10

Chapter 3. INSTRUMENTATION 16
3.1 Materials 16
3.2 Surface Laser Light Scattering 18

Chapter 4. RESULTS AND DISCUSSIONS 23

Chapter 5. SUGGESTIONS FOR FUTURE WORK 35

Reference 38

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