= Coil-globule transition
The change of an isolated flexible <polymer> from an expanded coil toward a dense <polymer globule> as its <solvent> becomes less favorable. In the <Flory approximation>, $F/(k_BT)\sim R^2/(Na^2)+vN^2/R^3+uN^3/R^6$, where the positive three-segment coefficient $u$ prevents collapse to zero size. Positive $v$ gives swollen-coil scaling, $v=0$ gives the <theta temperature> condition, and negative $v$ favors a dense state with $R^3\sim uN/|v|$. Finite chain <length> rounds the change; <polymer aggregation> is a distinct multi-chain process and must be controlled in an experiment.
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