Now as we increase the temperature,
the entropic contributions become more important.
Now the dipole ordering where the sodium ions look for
the favorable dipole ends is energetically favorable.
However, this comes at the loss of rotational entropy.
Now as you increase the temperature, the entropy begins to take over,
and more of these water molecules move away from the shielding region.
This leads to a weakening of the shielding, and
as a result, the dielectric constant drops as a function of temperature.
Another important consequence of the dipoles present in water
is the emergence of hydrogen bonds.
Now hydrogen bonds occur when the partial positive charge on the hydrogen atom
interacts with the negative charge on the oxygen atom of an adjacent water molecule.
Now, the strength of the hydrogen bonds is extremely strong, and
is 8 times the thermal energy at room temperature.
Now, just to get a sense of the hydrogen bonding energy scale,
this is about as energetic as the thermal energy associated with
a furnace sitting at 2,400 degrees Celsius.
Now, because water likes itself so much, when a substance that cannot form
hydrogen bonding is added to water, the substances are simply excluded from water.
This effect is known as the hydrophobic effect.
The most common one that we encounter in our daily lives is oil and water.
The most beautiful, biological example of hydrophobicity is the lotus effect.
The lotus effect is where the leaves of the lotus flower
repel water quite strongly, and they're strongly hydrophobic.
So when water droplets are dropped on the leaf,
they rapidly move around the lotus leaf.
While doing so, the water picks up the dirt particles.
Now this happens because the micro and nanoscopic
architecture of the surface minimizes the droplet's adhesion to that surface.
Now what practical applications do these things have?
Superhydrophobic coatings are emerging in a wide variety of applications.
Now, wouldn't it be wonderful
if you would never have to wipe your car windshield again, right?
All we have to do to enable this is somehow mimic the lotus leaf.
Now glass coatings are being developed by covering a surface with hydrophobic,
extremely water resistant and hydrophilic,
extremely water absorbent nanopolymers that can work together.
Now when a fluid lands on that surface, it is repelled from certain regions,
the hydrophobic regions, and attracted to others, the hydrophilic regions.
Now these serve to guide the flow.
How would a super-hydrophobic windshield look and work?
Well there have been traditionally very few surface coatings on windshields.
Most people just wait for
their car to get dirty, then clean the windshield with wiper fluid.
Now this can sometimes leave unsightly streak marks.
And most fluids are hopeless against greasy messes like bird droppings.
Now using super hydrophobic nano coatings on a windshield is a distinctly modern
invention where the water droplets are guided off the glass surface and
other fluids simply cannot stick.
This leaves the driver's field of vision completely clear,
leading to safer driving experience.
Now we've discussed a lot of wonderful things about water,
but water can't be all good, can it?