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5.3 Binary systems without and with one additional noncritical relaxation term

used to determine the cell length of the resonators. The critical parameters like critical mole fraction xc and the critical temperature Tc of investigated systems are given in Table (5.2) for binary systems without or with one additional noncritical relaxation term, and in Table (5.3) for binary systems with complex background contributions.

critical mixture critical conc. xc in mole frc. critical Temp. Tc of first component [K] n-pentanol-nitromethane (PE-NM) 0.385 300.95 nitroethane-3-methylpentane (NE-3MP) 0.500 299.68 nitroethane-cyclohexane (NE-CH) 0.452 296.46 methanol-hexane (ME-HEX) 0.500 307.74 ethanol-dodecane (ET-DOD) 0.687 285.82

Table 5.2: Critical composition and temperature of binary systems without or with one additional noncritical relaxation term.

critical mixture critical conc. xc in mole frc. critical Temp. Tc of first constituent [K] isobutoxyethanol-water (i−C4E1/H2O) 0.070 298.10 2,6-dimethylpyridine-water (2,6-DMP-H2O) 0.065 306.83 triethylamine-water (TEA-H2O) 0.076 291.36

Table 5.3: Critical composition and temperature of binary systems with complex back- ground contributions.

5.3 Binary systems without and with one additional noncritical relaxation term

Because of the complexity of the Bhattacharjee-Ferrell formalism, it is useful to first study critical systems for which additional chemical relaxation contributions in the range of frequencies of measurements are not expected in the ultrasonic spectra. It was thus in- teresting to perform investigations into the critical dynamics of binary mixtures of critical composition, such as n-pentanol-nitromethane (n-PE-NM) [76], nitroethane-cyclohexane (NE-CH) [90], methanol-cyclohexane (ME-HEX) [93], ethanol-dodecane (ET-DOD) [99], as well as nitroethane-3-methylpentane (NE-3MP) [86], for which no such contributions from elementary molecular processes are expected.

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