Subject: What properties make some materials gain e- by contact (

I'm looking for a pattern.  Some polymers (nylon, wool) tend to give up 
electrons easily and become positively charged with "static electricity", 
while other polymers (rayon, silk, polyester) tend to gain electrons.  Does 
the polymer being a protein matter?  Does beiong a polymenr have anything 
to do with it (after all, glass canbe charged easily)?  Is there any 
pattern at all?  What properties of the material make it a "keeper" or 
"looser" of electrons?  I am dying to know and haven't found anything yet 
on the web.  

Re: What properties make some materials gain e- by contact (