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Thermal Lens Calorimetry

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Thermal Lens Calorimetry

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    1. Thermal Lens Calorimetry Ashleigh Baber Dr. Seidman Karishma Rajani Summer 2004 Randolph-Macon Womans College

    2. Thermal Lens Phenomena

    3. Divergence

    5. Experimental Design

    6. Experimental Design without Sample

    8. Experimental Design

    11. Why Calibrate the Procedure? The appearance of the waveform is affected by factors such as: Distances between components on the optical rail Laser power Frequency of the chopper Aperture diameter All factors except for the aperture diameter are kept constant.

    12. Method for Calibrating the Procedure Prepare a set of standard solutions using indophenol blue dye and liquids with known heat capacities. Measure the bloom diameter and vary the aperture of the diaphragm until the correct time constant is obtained. Aperture diameter is plotted versus Bloom diameter and the result is a straight line. This graph may then be used as a calibration curve for finding the heat capacity for unknowns. Amy Payne found that with larger bloom diameters came larger aperture diameters.Amy Payne found that with larger bloom diameters came larger aperture diameters.

    14. Determining the Cp of Unknowns A solution is made with indophenol blue dye and a liquid with an unknown heat capacity. The bloom diameter is measured and using the equation for the line, the aperture diameter is calculated. Several trials are conducted with the calculated aperture diameter to find an average time constant which is plugged into the equation to find the heat capacity.

    16. Results A range of absorbances fit on one line, reducing the time necessary for sample preparation. Error in heat capacities are random, due to the precision of the oscilloscope. It seems as though this method could be as reliable as solution calorimetry and it has the potential to be faster.

    17. Experimental Design

    20. Proposed Procedure Prepare an unknown so that the absorbance falls within the range. Measure the sample to diaphragm distance. Calculate the slope and y-intercept from the calibration lines. Determine the bloom diameter. Calculate the aperture diameter and run the sample. A.D. = slope *B.D. + y-intercept

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