Isotope-induced quantum-phase transitions in the liquid state.

Isotopic binary liquid mixtures are universally characterized by an upper critical solution temperature as a consequence of zero-point motion, in conjunction with the anharmonicity of the interatomic potential. This quantum effect is predicted, and demonstrated by small-angle neutron scattering measurements, to be manifest at ambient temperatures for mixtures of deuterated and protonated polymers. Prior evidence of such phase behavior has been restricted to liquid mixtures of helium-3 and helium- 4.