8
$\begingroup$

Is it possible to create hydrophobic water?

Two species are phobic within some medium under some conditions when they don't here together (cohere if they're the same species; adhere otherwise). To be clear: phobic species don't really repel so much as they're not very attracted to each other. Species can become self-phobic. Of course, it's important to remember that members of the species aren't repulsing others of their own kind so much as just aren't very attracted to them. And then since they're not really attracted, they do the natural thing and just tend to disperse, filling the volume containing them. In other words, they vaporize. Water can be vaporized, e.g. through heating.

In the question I linked above the third answer says that since the water molecules do not attract each other in gaseous state they are hydrophobic. Even if the water molecules are not hydrophilic are they thus necessarily hydrophobic?

$\endgroup$
2
  • 2
    $\begingroup$ Otoh. water condenses from the gas phase, so it must be hydrophilic. ;) You see these categories make no sense for gases. $\endgroup$
    – Karl
    Jul 7 at 12:59
  • 1
    $\begingroup$ To address the title itself, being hydrophilic/hydrophobic is rather being somewhere on a continuous gray scale than inside of either black either white box. $\endgroup$
    – Poutnik
    Jul 8 at 9:26
6
$\begingroup$

Two water drops 1 mm apart do not attract each other, if I omit gravity and electrostatic charges. Are they hydrophobic ? No, they are not. The relevant intermolecular forces are contact ones, decreasing very fast with high power order of distance.

Water molecules in a gaseous phase have still strong attraction during their collisions, what reflects in vapor being far from an ideal gas. The estimated boiling point of water, assuming absence of hydrophilic hydrogen bonds, is about $\pu{-120 ^{\circ}C}$. This gives some idea what makes pure water vapor to condensate at $\pu{+100 ^{\circ}C}$ ( at $\pu{101 325 Pa}$ ).

Hydrophilicity means having comparable strength of intermolecular bonds as water has, to itself as well as to water molecules. Mutual mixing often releases energy ( ethanol + water ) and is supported by entropy increase too.

Hydrophobicity means having weak intermolecular bonds, to itself as well as to water molecules. Breaking mutual strong bonds between water molecules to create weak bonds with the hydrophobic substance is not energetically favored.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.