Interiors of the Outer Gas Giants 

Things to think about:
The Phase Diagram revisited

Differences from Jupiter:

Why does Saturn have a high temperature?

Liquid hydrogen and liquid helium are immiscible - they do not mix (like oil and water).

But Uranus & Neptune are not primordial composition (they have more heavy elements), so this phase analysis may not be particularly applicable to them.

Instead of pressure ionizing hydrogen, in U & N, we may have ionized water (particularly H 3O+ and OH-) forming an ionic ocean deep inside the planets. Such an ionic ocean can dissolve ammonia, but not methane -- U & N have methane rich atmospheres.

Danger: these are not oceans like the Earth's, but rather material in liquid states at high temperature and densities. No surfing allowed!