Why membrane for distillation has to be hydrophobic

[Yinxiao Li]

I have a question about membrane distillation. I have read the following from a review paper about membrane distillation: The membrane distillation should be applied for membrane operations having the following characteristics:
- The membrane should be porous.
- The membrane should not be wetted by the process liquids.
In other words, this membrane has to be hydrophobic. However, I don't think the membrane distillation has to be hydrophobic, except for direct contact membrane distillation...A hydrophilic membrane can be applied to air gas MD, sweeping gas MD and vacuum MD, correct? Or there is any reason that hydrophilic membrane won't work.

 

[DaveC426913]

It seems to me that if the membrane were hydrophilic, it would allow (in fact, encourage) the liquid water to creep by capillary action (due to liquid water's surface tension) through the pores. Hydophobia is what holds the liquid back, even when the pores are considerably larger than the molecules.

As water has strong dipole characteristics, whilst the membrane fabric is non-polar, the membrane material is not wetted by the liquid. Even though the pores are considerably larger than the molecules, the liquid phase does not enter the pores because of the high water surface tension. A convex meniscus develops into the pore. This effect is named capillary action.

https://en.wikipedia.org/wiki/Membrane_distillation#Principle_of_membrane_distillation

Not bad, I think, for someone who had never even heard of membrane distillation until five minutes ago?