One aspect of glasses that has confused me was the fact that the transition temperature Tg drops as you slow the rate of cooling. This has confused me because if the glass is slowly becoming more crystalline, then I would of thought that the Tg would start climbing up towards the crystal melt point (Tm is it?) as by cooling it slower, the molecules would have more time to organize themselves. One of the ways I was trying to reason this out, was that in the case that you cool glass quicker, the less ordered amorphous result would require you to put in my energy to allow the glass molecules to move around since there are less directions in which the lattice can slide in since very little of it is crystalline. Since cooling it slower allows a more crystalline structure to form, the Tg temperature drops since there are more directions in which the molecules can move (easier to form dislocations I guess...?). However (if my visualization above at all is at least somewhat true) I would think that there must be a point where the binding energy of the lattice starts to reduce the mobility of the molecules; ie if you cool it slowly enough you do actually create a crystal, so there must be a point where Tg starts to increase for a very slowly cooled glass (which eventually starts looking like a melting point since the viscousity would become so high as to be almost indistinguishible from being solid). I guess i'm looking to understand why Tg drops when the binding energy increases in slowly cooled glasses; and the above explanation kind of makes sense to me, but I might be looking at it the wrong way. Any one have any good explanations for the drop in Tg for glasses that are cooled slower? Thanks!