Modular Design of a TEC Cryomicroscope System and Freezing Experiments of Microcapsules

• Main Authors: Tai-Lin Wu, 吳岱霖
• Other Authors: 林達德
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/38224768696251017878

碩士 === 臺灣大學 === 生物產業機電工程學研究所 === 95 === In this study, we use the thermoelectric cooler (TEC) whose surface temperature can be controlled by adjusting the direction and magnitude of its current to improve the cold stage and cooling system of a cryomicroscope system. The temperature control circuit and the integrated software were also elaborated to make the cryomicroscope a modular system which is convenient to use. The original temperature control system using liquid nitrogen, heater and refrigerated circulation bath were replaced by the small-size TEC cold stage and cooling system. For different experimental demands, the TEC on the cold stage can be changed from single-stage TEC to tri–stage TEC. The lowest temperature achieved was −68.6°C while the highest cooling rate was −120°C/min. For the isothermal control of the cryomicroscope, the error of temperature was less than 0.1°C and the absolute mean error was 0.0647°C. Experiments were also performed to study the IIF behavior of microcapsules of various sizes by the cryomicroscope. It was observed that the microcapsules behaved as osmometers that water migrated across the cell wall when there was an osmotic potential. During freezing, IIF phenomenon of microcapsules occurred immediately after the ice front touched the microcapsule following the seeding of the supercooled solution. When the external solution was changed to glycerol solution of different concentrations, the IIF temperature decreased as the concentration of glycerol solution increased. When alcohol was used as external solution to preclude external ice formation during freezing, we observed that the smaller the microcapsule the lower the IIF temperature, and the variation of IIF temperature for microcapsules of the same size was small. When glycerol or alcohol was permeated into microcapsules due to the principle of osmolarity, the time when IIF occurred was delayed as well as the IIF temperature was lowered when the ice front touched microcapsules during freezing. Additionally, when we increased the concentrations of glycerol or alcohol concentration inside the microcapsules by permeation, the IIF temperatures of microcapsules decreased noticeably when the concentration increased.