Study of Thermal Diffusion Forced Rayleigh Scattering in Binary Mixtures of Solution
| Autor: | Lin, Chenghan, 林承漢 |
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| Rok vydání: | 2012 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 100 In this thesis, we use the thermal diffusion forced Rayleigh scattering (TDFRS) technique to investigate thermal diffusion properties of two binary mixtures of solutions: carbon disulfide-ethanol and methanol-ethanol. A small fraction of methyl red dye is dissolved in both solutions as the light absorber of 532 nm light. We use two CW Nd:YVO4 laser beams at 532 nm as the pumps, also referred to as writing beams, and a CW He-Ne laser beam at 632.8 nm as the probe, namely the reading beam. The pump beams intersect in the solution and create a thermal refraction grating in both solutions which diffract the probe beam. By measuring the power of the diffracted 632.8 nm light as a function of time, we investigate thermal diffusion properties of the binary solution mixtures evolve with time. In the theoretical aspect, we start from Fick's law of fluid mechanics and derive the relation between mass flux of the binary solution mixtures and the driving force of mass flow according to the Maxwell-Stefan equation. This helps to deal with mass diffusion. Afterwards, we combine the abovementioned mass diffusion and thermal diffusion, a concept of thermal dynamics, as the overall driving force of mass flow. Here the relation involving both mechanisms is named the Onsager-Casimir relation. From this relation, we derive the variation of (thermally induced) refractive index with time. In the experimental aspect, we measure the diffracted signal of the binary solution mixtures under various experimental conditions: different ratio of the individual solution concentrations, different grating periods and different polarization combinations of the writing beams. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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