Pathlength difference correction

The experimental and data reduction procedures are essentially the same as for the static cell experiments. The gas temperature is obtained using a fine wire, radiation-corrected thermocouple. The cold mixing layer at each flame boundary is accounted for by using an effective pathlength (8.0 - 8.2 cm, depending on the fuel-air equivalence ratio) which differs slightly from the actual burner length of 8.6 cm. Fuel-air equivalence ratios of... 

To use the constant thickness film maker, a spacer ring of a given thickness is placed in the bottom half of the device along with the sample. The other half of the device is put in place on top of the sample. The entire unit is then placed between the heated platens of a hydraulic press. Once the correct temperature is reached, the sample will soften and flow and fill the space between the top and the bottom of the unit. The film thus formed will be of the same thickness as the spacer ring. Spacer rings of different thicknesses are available to give films of different pathlengths. A small hole in the side of the device allows excess polymer to flow out. Once the device is removed from the press and the polymer film is allowed to cool, its spectrum is measured like any other heat and pressure film, as described above. 

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