Calculating Thickness of PTFE Membrane Air Filter

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SUMMARY

The discussion focuses on measuring the thickness of PTFE membrane air sampling filters using light transmission data. The unexposed filter has a known thickness of 40μm, while five exposed filters exhibit varying mass concentrations and light intensity readings after exposure to a 1460 lux light source. The equation I1d12 = I2d22 is proposed for calculating thickness, but several critical questions arise regarding the assumptions of linearity in light transmittance, the dimensions of the filters, and the effects of saturation on light attenuation. The conversation highlights the need for clarity on these factors to accurately determine the attenuation coefficient of each filter.

PREREQUISITES
  • Understanding of light transmission principles and attenuation coefficients
  • Familiarity with PTFE membrane properties and their applications
  • Knowledge of basic photometry and light intensity measurement
  • Experience with experimental design and error analysis in research
NEXT STEPS
  • Research the application of the Beer-Lambert Law in measuring filter thickness
  • Explore methods for determining the saturation point of PTFE membranes
  • Investigate the impact of filter dimensions on light transmittance
  • Learn about the effects of wavelength on light absorption in membrane materials
USEFUL FOR

Researchers, environmental scientists, and laboratory technicians involved in air quality monitoring and filter analysis will benefit from this discussion.

laramman2
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Homework Statement


Is there any way we can measure the thickness of an exposed PTFE membrane air sampling filter? An unexposed filter (from the filter datasheet) has a thickness of 40μm. We have 5 ambient air exposed filters with the following mass concentrations: 1μg/m3 (filter 1), 20.1 μg/m3 (filter 2), 40.6 μg/m3 (filter 3) , 60.1 μg/m3 (filter 4) , and 66.1 μg/m3 (filter 5) . Also, for each filter, we performed a procedure where we transmit a 1460 lux constant light source through the filter and the reduced light intensity was captured by a light sensor. The data for that procedure are as follows:

CONTROL - 1460 LUX
FILTER 1 - 418 LUX
FILTER 2 - 375 LUX
FILTER 3 - 295 LUX
FILTER 4 - 185 LUX
FILTER 5 - 130 LUX

Btw, this is for our research. We try to determine the attenuation coefficient of each filter.

Thank you very much!

Homework Equations



I1d12 = I2d22

The Attempt at a Solution


Does the above equation possible to use?
 
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Lots of questions about this one. Are the membranes saturated? Are you assuming linear scaling of light transmittance to thickness? Are the filters the same length and width in dimension? How does light attenuation scale with thickness of unsaturated membranes? How does light transmission vary in saturated vs unsaturated samples? Is the light absorbed differently for saturated vs unsaturated at that particular wavelength? Is it a single wavelength source?
What sources of errors are in your measurements?

Finally, this section is for homework problems. If this is for research then the Faq states this is not the place to put this question.