Hydrophobic effect
= Hydrophobic effect
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The <hydrophobic effect> is the solvent-mediated tendency of <nonpolar> regions to associate in <water>. Exposing a <hydrocarbon> region changes how surrounding <water> <molecules> can arrange and interact; reducing that exposure can lower the total <free energy>. Both <water> and <lipids> enter the accounting. The effect is not an additional <covalent bond> between chains. See https://goldbook.iupac.org/terms/view/H02907[IUPAC Gold Book: hydrophobic interaction].
At fixed <temperature> and <pressure>, compare two candidate organizations by the change in <Gibbs free energy>, $\Delta G=\Delta H-T\Delta S$, where $H$ is <enthalpy>, $T$ is absolute <temperature>, and $S$ is <entropy>. An organization with lower $G$ is favored in this comparison. Reducing exposed <hydrocarbon> area is one contribution; changes in chain packing and the <entropy> of the <lipids> also matter. This explains why <hydrophobicity> alone cannot predict every aggregate shape. See <Chemistry 2e by Paul Flowers and others/16.4 Free Energy>.