Toda Ohira and Ikeda in their article 'Micro-gas analysis system
microGAS comprising a microchannel scrubber and a micro-fluorescence
detector for measurement of hydrogen sul�de' spin PDMS to create a
thin membrane for use as a gas permeable membrane.  They have a plot
of spin speed vs PDMS thickness.  For a thickness of about 10 um they
use a spin speed of 5000 rpm.

Good luck

Dr Matt Davies
Post-Doctoral Research Assistant
Science & Technology Research Institute
University of Hertfordshire
College Lane
HATFIELD        AL10 9AB
UK

e : [email protected]