[8-Ball]

I'd be very interested to speak to this chemistry teacher.

To say that;

"copper is metallic, and thus really a frozen liquid at room temperature, with a jumbled up molecular structure"

Is a bit off the mark.

Copper is crystalline and ordered. It follows a face centered cubic close packed pattern. The difference between copper and diamond is the type of bonding between adjacent atoms, as well as the crystal structure.

The reason diamond has a far superior conductivity is because the carbon atoms are bonded covalently. Covalent bonds are rigid and can transfer phonons (atomic scale vibrations) with great ease.

The reason why a copper diamond composite is used is to allow the formation of various shapes. It is also much easier to produce regular diamond particles than a large solid diamond with few flaws.

By sintering the diamond particles with powdered copper, it will form a suspension of diamond particles in a copper matrix. If the mixture is right, then the copper will be sufficient to fill the gaps between the particles, providing both strength and a thermal interface, while not separating the diamond particles to any great degree.

8-ball