I have been trying to understand what determines the heat conductivity of solid pure substances (i.e. NOT composites) that have no air gaps and is an electric insulator. For example, why is the heat conductivity for nylon so much less than that for diamond? -there is bound to be some difference but I don’t understand why it is such a BIG difference ( AT LEAST a 3600 fold difference!!! -why such a massive difference!!!? ). I tried looking this up on the net but I didn’t get at far as I would have liked:
-it says for an electric conductor:
“…freely moving valence electrons transfer not only electric current but also heat energy….”
Ok, I have no problem with that. But I am straining to understand what determines the heat conductivity of an electric insulator (consisting of a pure substance and with no air gaps) such a nylon etc
-it goes on to say:
“…However, the general correlation between electrical and thermal conductance does not hold for other materials, due to the increased importance of phonon carriers for heat in non-metals. …”
So I looked up phonon carriers ( http://en.wikipedia.org/wiki/Phonon ) and found this to be VERY complex and difficult to understand!
-so this is what I want to ask -is there any ‘rules of thumb’ that we can use to estimate the heat conductivity of a electrically-insolating solid pure substance with no air gaps such as nylon etc that doesn’t involve horribly complex mathematic? -I mean, can you get an estimate of the heat conductivity of such a substance just by knowing, for example, what proportion of the chemical bonds are C-C bonds and proportion of the chemical bonds are C-N bonds etc?
I also got this from: http://en.wikipedia.org/wiki/Thermal_conductivity
“….Dense gases such as xenon and dichlorodifluoromethane have low thermal conductivity. An exception, sulfur hexafluoride, a dense gas, has a relatively high thermal conductivity due to its high heat capacity….”
What does its high heat capacity got to do with it? -I mean, why should a high heat capacity make the thermal conductivity higher? -and is this true just for gasses or is this true regardless of whether it is a gas/liquid/solid?
I would greatly appreciate any insight into this as this has long puzzled me.