Theta temperature
= Theta temperature
{title2=$\Theta$}
The <theta temperature> is the temperature at which the leading effective two-segment interaction of a dilute long <polymer> vanishes, so its large-scale size is approximately that of an <ideal chain>. In the simplest <Flory–Huggins solution theory> this is the condition $\chi=1/2$. It is the infinite-chain limit of the upper critical temperature in the usual energetic model, not the critical temperature of every finite chain.