Microfluidic devices for gas flow control

1
Gas Contamination Pre-Concentrators

• M.S. Silvana Gasparotto de Souza (Ph.D. student)

• Dr. Rogerio Furlan

• Dr. Maria Lucia Pereira da Silva

2
Basic Structure

• Use of microchannels (silicon and modified) to
  concentrate pollutants (hydrocarbons present in
  the air)

• Easily portable and mobile detection system

• Low cost batch fabrication

3
Microchannel Technology

• Ports open with KOH or TMAH etching

• Microchannel isotropic etching RIE SF6 based

100 µm wide 40 µm deep 30 cm long 3 cm x 3 cm area

• Silicon -glass anodic bonding

4
Tests

• N2 1000 ppm n-hexane leak detector

• N2 0.1 n-hexane 0.1 He mass spectrometer

5
Results with N2 1000 ppm n-hexane
Without microstructure
With microstructure

• With microstructure nitrogen flow is observed at
  the output but n-hexane is not detected before 50
  min.

6
Results with N2 1000 ppm n-hexane
Heating up the microstructure after n-hexane
adsorption (200 C in 5 sec)

• With N2 a single pulse of n-hexane was obtained
  after a delay time of 7 sec from the
  beginning of the heat slope

• Without N2 the pulse grows large, taking 3 sec to
  n-hexane to be completely removed, with a delay
  time of 7 sec

• Differences in weight before and after adsorption
  of about 1 mg were easily found

7
Results with N2 0.1 n-hexane 0.1 He

• Typical mass spectrometry spectrum

8
Results with N2 0.1 n-hexane 0.1 He

• Similar behavior to that obtained with leak
  detector

9
Improvements of the microstructure

• Holes drilled in the glass before anodic bonding

• Porous silicon formation inside the microchannels

10
Conclusions

• Silicon microchannels proved to be effective to
  be used as pre -concentrators for high-polluted
  gas mixtures

• Tests for use with small concentrations of
  contaminants and the use of porous silicon to
  improve adsorption are being performed