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5 Experimental Verification of Dynamic Scaling Theories and Discussions

5.2 Preparation of critical mixtures

substance formula supplier purity molar mass [g/mol] n-butanolr C4H10O Fluka ≥99% 74.12 waterr H2O deionized 18.00 and bidistilled nitromethane CH3NO2 Fluka ≥99% 61.04 n-pentanol C5H12O Fluka ≥99% 88.15 nitroethane C2H5NO2 Aldrich ≥99.5% 75.08 3-methylpentane C6H14 Aldrich ≥99% 86.20 cyclohexane C6H12 Aldrich ≥99.5% 84.16 methanol CH4O Fluka ≥99.8% 32.04 n-hexane C6H14 Aldrich ≥99% 86.18 ethanol C2H6O Fluka ≥99% 46.07 n-dodecane C12H26 Aldrich ≥99% 170.34 isobutoxyethanol C6H14O2 Wako ≥97% 118.17 2,6-dimethylpyridine C7H9N Aldrich ≥99% 107.15 triethylamine C6H15N Aldrich ≥99% 101.19

Table 5.1: Substances used: index r denotes substance also used for reference measurements and calibrations.

All non-aqueous constituents of the mixtures presented in Table (5.1), have been used as delivered, except for the substance isobutoxyethanol which was additionally purified by fractional distillation at 318 K and at a reduced pressure of 23 mbar in a concentric tube column of 64 real plates. This distillation procedure has been performed several times, to get isobutoxyethanol surfactant as pure as possible. Before preparing mixtures, the con- stituents were degassed in an ultrasonic bath or vacuum oven. This preparation step was done to avoid gas bubbles that might grow in the cells during measurements. In order to avoid preferential evaporation, the degassing in a vacuum oven has been performed before preparing the mixtures. Finally, mixtures have been prepared under nitrogen gas atmo- sphere by weighing appropriate amounts of the constituents into suitable flasks. Uptake of water from the air was avoided thereby. The critical point of a mixture was determined visually by taking into account the criterion of critical opalescence as well as the criterion of equal volume (Section 2.3.5). Additionally, the existence of the critical point has been determined by densitometer measurements (Anton Paar 5000) in Section (3.4). In the case of ultrasonic measurements, calibrations for resonator losses were performed after- wards, using reference liquids: butanol for mixtures listed in Table (5.2) and deionized bidistilled water for aqueous mixtures listed in Table (5.3). In addition, water has been

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