ratio is approximately 0.03 for the 0.5 wt % Pt/TiOz sample. Even for the hypothesis of a partial coverage of the pt, atoms by anions (note that we have ruled out this hypothesis on the basis of the radiotracer adsorption data), it follows that this would have contributed to the total charge of the Ti02 grains insignificantly, which is not in accord with the results: the electrophoretic curve of the powder containing 0.5 wt % Pt is clearly distinct from that of TiOz. Furthermore, the shifts of the other curves are not proportional to the Pt content (Figure 5), as would be the case for the adsorption of negative species on Pt, atoms. ConclusionFrom (i) a comparison of the charge densities in different parts of the double layer for naked TiOz and a 10 wt % Pt/Ti02 sample, (ii) the electrophoretic mobilities of both these samples in NaCl ~ (33) In this paper the periodic group notation (in parentheses) is in accord with rexent actions by IUPAC and ACS nomenclature committees. A and B notation is eliminated because of wide confusion. Groups IA and IIA become groups 1 and 2. The d-transition elements comprise group 3 through 12, and the pblock elements comprise groups 13 through 18. (Note that the former Roman number designation is preserved in the last digit of the new numbering: e.&, I11 -3 and 13.) and in NaNO, solutions, and (iii) the distinct shift of the electrophoretic curve of a 0.5 wt % Pt/TiOz specimen with respect to that of naked Ti02 as compared with the very weak Pf/TiOH ratio, it can be inferred that the differences observed by potentiometry ( Figure 4) and electrophoresis ( Figure 5) for various Pt/Ti02 samples really stem from the effect of the deposited Pt particles on the Ti02 acid-base properties. As the Pt content increases, the acidity of the titania hydroxyl groups increases as shown by the PZC and PZZP variations (Table I). Consequently, for catalytic or photocatalytic reactions in which the aciditybasicity of the surface is involved, one should keep in mind that the properties of naked Ti02 are altered by the platinum deposit. The increased acidity is consistent with a smaller number of free electrons in TiOZ with deposited Pt than in bare Ti026s7 because of the alignment of the Fermi level of both materials. In other words, it is not unexpected that changes in the bulk properties of the semiconductor should be reflected in its surface properties. Acknowledgment. We thank Mrs. M.-N. Mozzanega for the preparation of the samples, Mrs. C. Carquille for her help with the potentiometry measurements, and Mrs. A. Chambosse and Mr. H. Urbain for the analyses of the Pt contents.A novel technique is described for the measurement of the partial molal volume at infinite dilution of solutes in supercritical fluids. Results are reported for five systems from 2 OC above the solvent critical temperature up to 15 O C above, at pressures from just above the critical pressure to 350 bars. The solute partial molal volumes are small and positive at high pressures, but very large and negative in the highly compress...

A cosurfactant-free O/W microemulsion composed of oil, a mixture of hydrophilic and hydrophobic surfactants, and water has been developed using food-grade components as a nutrient delivery system. We started our investigation to monitor the phase behavior of this system based on a hydrophilic surfactant (Tween 80). From a phase diagram, the weight ratio of 5.4:33.8:60.8 = oil:surfactant:water was selected as a combination ratio for the O/W microemulsion system. We also investigated the combination effect of different hydrophobic surfactants to Tween 80 on microemulsion formation. Use of hydrophobic surfactants with Tween 80 produced smaller droplets than Tween 80 alone. Rheological studies showed that all microemulsions followed shear-thinning behavior. The turbidity of microemulsions did not change after accelerated stability tests, indicating that this microemulsion system was stable under the given harsh conditions. When docosahexaenoic acid (DHA) oil was applied to this microemulsion system, the particle size and the turbidity were not significantly changed. Dilution with a different aqueous medium, either water or acidic fluid, did not significantly change the microemulsion turbidity. DHA oil incorporated in microemulsion showed higher oxidation stability than free DHA oil.