Aqueous oxygen near the homogeneous nucleation limit of water: stabilization with submicron capillaries

Previous studies have demonstrated that the metastability threshold of aqueous oxygen (AO) is inversely dependent on the internal diameter of capillary tubes used to deliver it into blood. The hypothesis was tested herein that significantly higher thresholds are attainable with capillaries having markedly smaller dimensions (submicron) than those previously studied. Water was equilibrated with oxygen over a 0.3- to 0.7-k bar range. Inert gases (argon, helium) facilitated studies at pressures to 2.5 k bar. An argon-ion laser was used to visualize fluorescein in the liquid effluent from silica capillaries that were tapered at the distal end to a submicron internal diameter (0.5 +/- 0.3 microns). During infusion of the fluorescent effluent into host water at 21 degrees C and atmospheric pressure, integrity of the effluent and lack of microbubbles were monitored by videomicroscopy. No microbubbles were noted at AO concentrations ranging from 7.5 to 12.8 ml O2/g (0.34 to 0.68 k bar, respectively) or in the aqueous argon effluent at concentrations to 14 ml Ar/g (0.75 k bar). For aqueous helium, effluent nucleation was not observed at a mean concentration of 13 +/- 3 ml He/g (2.0 +/- 0.5 k bar), with an upper value of 15.2 ml He/g (2.4 k bar). The data represent the highest values of the tensile strength of water ever observed and approximate its theoretical homogeneous nucleation limit. Thus, remarkably high metastable concentrations of AO and other gases are attainable with the use of submicron capillaries.