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Siegel der Universität
Department für Chemie - Arbeitsgruppe Prof. Strey

Blasenbildung in gasgesättigten Flüssigkeiten: Der Nachweis homogener Keimbildung

Bernd Rathke, Mai 2002

Bubble formation in liquids is, contrary to gas phase condensation, poorly understood. Within the frame of the present work, the process of bubble formation in the binary system n-hexadecane / carbon dioxide is examined. To this end nucleation pulse method developed for gas phase nucleation is adapted to bubble formation. A corresponding nucleation pulse chamber has newly be assembled. The apparatus permits using static light scattering measuring bubble number densities in the range 102 < NV / cm3 < 106 by virtue of ultra-fast pulses of duration of 0.2 < ?t / ms < 0.5. Stationary homogeneous nucleation rates are then calculated from J = NV / ?t. In addition to model-independent determination of nucleation rates, measurements of bubble growth under variable, albeit well-defined conditions is feasible. Nucleation pulse investigations have the further advantage of model-independently providing the volume V* of the critical bubble (25 < V* / nm3 < 30). Characterizing the binary system, a p(x)-diagram is obtained, which at a temperature of T = 40 °C shows a liquid-gas coexistence as well as a liquid-liquid coexistence - differing from literature. The critical pressure of the latter coexistence is located at 165 bar. Based on the known phase diagram, bubble formation experiments were conducted at pressures ranging from 1 to 175 bar. Nucleation rates in the range 107 < J / cm-3s-1 < 1011 were measured. The nucleation rates determined indicate a complete failure of the classical nucleation theory in case of bubble nucleation.