Debashis,

               Just guessing but I would assume the CH3 surface reaction
is the correct approach.  When using vacuum vapor prime to change the
surface tension for resist adhesion this is the reaction.  The SiO2
surface has ample O-H ions.  Treating with HMDS NH-Si2(CH3)3 the NH
takes the H from the O-H when 2 H atoms have been taken NH3 is liberated
and the 2 Si(CH3)3 molecules adhere to the O.  This can be seen over
time as the hydrophobicity is measured. 22 degrees starting, 1 minute of
prime 45 degrees, 2 minutes of prime 56 degrees, 3 minutes 52, 4 minutes
70, 5 minutes 75 degrees.  Because the CH3 is sticking up to the outside
world.  Bill Moffat

________________________________

From: mems-talk-bounces@memsnet.org on behalf of DEBASHIS MAJI
Sent: Fri 5/29/2009 11:46 PM
To: General MEMS discussion
Subject: [mems-talk] Hydrophobic recovery of PDMS


Hi All,

I have a doubt regarding the hydrophobic recovery of PDMS. It is explained
that the hydrophobic recovery is due to the slow diffusion of the Lower
molecular weight PDMS components to the top surface thus rendering the
surface hydrophobic again. Here I have a doubt regarding, which lower
molecular weight ( compared to which heavier MW ) gets diffused in? Is it
the -CH3 ( MW-15) polymeric chain that slowly diffuses in to replace the
hydrophilic -OH group ( MW-17)?  Any sort of help shall be highly
appreciated.