60 HIGH PERFORMANCE POLYMERS
After a thermal treatment of the parylene-C coat-
ings by annealing at 180
◦
C for 24 h, the water dif-
fusivity reduced by a factor of 2. This phenomenon
was attributed to an increase in crystallinity and the
evolution of a new crystalline phase in parylene-C.
2.5.12 Ultrafiltration Membranes
The surface of a porous poly(ether sulfone) mem-
brane film can be modified by the deposition of a
nanoporous parylene film [121]. The addition of glyc-
erin vapor during the deposition process of the pary-
lene prevents the parylene from forming over the
pores. So, parylene could be coated onto the poly(ether
sulfone) membrane while keeping some pores open
provided that the amount of dimer is properly con-
trolled.
The parylene-coated membrane ...