Abstract:

Critical compositions and critical temperatures of (2,6-dimethylpiperidine+water) and (2,6-dimethylpiperidine+heavy water) were determined. Coexistence curves of (T-n) (T is temperature and n is refractive index) for two systems were determined by the measurements of refractive indices of coexisting phases. Coexistence curves of (T-n) were converted to coexistence curves of (T-x) and (T-φ) (x is mole fraction and φ is volume fraction) through standard curves determined by the measurements of refractive indices at various mole fractions and temperatures. The experimental data were analyzed to obtain critical exponents (β), critical amplitudes (B), Wegner correction amplitudes (B1) and parameters for diameters (ρd) of coexistence curves. We found that when H2O was substituted by D2O in the system the low critical temperature decreased by 3.2 K while the critical exponent was also consistent with the three-dimensional Ising model (3D-Ising) value (0.327) near the critical point. The critical composition and shape of coexistence curves were almost unchanged.

Key words: Coexistence curve, Critical phenomenon, Refractive index, Deuteriumisotope