Heterogeneity of Critical Indexes at “Liquid–Liquid” Phase Transition in 2,6-Lutidine Aqueous Solutions: An 1H NMR Study

Temperature dependences of 1H nuclear magnetic resonance (NMR) splitting signals of 2,6-lutidine aqueous solutions were studied in the vicinity of lower critical solution temperatures. The splitting of 1H NMR signals was considered as an order parameter at “liquid–liquid” phase transition. It was discovered that critical indices to determine the behavior of the order parameter are different (i.e., demonstrate heterogeneity) for structurally non-equivalent hydrogen atoms of the 2,6-lutidine molecule. An isotope effect associated with van der Waals interactions was registered in the obtained 1H NMR spectra.