The structure variation of cellulose acetate (CA) reverse osmosis (RO)
membranes due to thermal annealing was investigated by using gas adso
rption. When the CA membranes were dehydrated by freeze-drying, the mo
rphology of the unannealed membrane was similar to that of the anneale
d membrane. On the contrary, with air-drying which induced structure c
ollapse of the CA membranes, gas adsorption behavior of the unannealed
membrane showed a significant difference from that of the annealed me
mbrane. The CA RO membrane in an unannealed state totally collapsed du
ring air-drying, but the membrane that was annealed for 10 min at 90 d
egrees C showed significantly reduced collapsing compared to the unann
ealed one. However, even though the CA membranes were annealed, use of
methanol as the wetting agent caused complete collapsing during air-d
rying.