PDMS/membrane solvent induced deflection measured by Veeco tool
PDMS/membrane deflection was measured on Veeco profiler by JP and me. The main problem with this kind of measurement is that it is taken form the backside of the membrane and the walls need to be excluded from the measurement. Using 20x objective helps but still has some problems.
PDMS was first spin-coated on the glass slide. PDMS thickness is approximately 2-3micron based on the spinning speed and dilution ratio. Then ozone treated pnc-Si membrane samples were attached to non-cured PDMS and the whole structure was cured on a hotplate. The samples attached were the ones with nine 100×100 micron windows so the whole area could be observed.
Addition of the acetone vapor produced visible deflection but the deflection was not measured. The top images are surface profiles before and after acetone introduction. The images below are actual membrane images at the same time.
Xylene was introduced next and it is known to severely swell siloxane polymers (more then 30%). The calculated deflection after xylene introduction is 0.45 micron. The data is below.
1.before xylene
2. after xylene
The 3D images showing xylene deflection are below (the color scale bars are different).
This first experiments show that the organic vapor permeates the membrane to swell the polymer sufficiantly. I will be trying thinner polymer layers and metal covered membranes to see how permeable they are next.