The morphologies, stabilities, and viscosities of high-pressure carbon dioxide-in-water (C/W) foams (emulsions) formed with branched nonionic hydrocarbon surfactants were investigated by in situ optical microscopy and capillary rheology. Over two dozen hydrocarbon surfactants were shown to stabilize C/W foams with Sauter mean bubble diameters as low as 1 to 2 microm. Coalescence of the C/W foam bubbles was rare for bubbles larger than about 0.5 microm over a 60 h time frame, and Ostwald ripening became very slow. By better blocking of the CO(2) and water phases with branched and double-tailed surfactants, the interfacial tension decreases, the surface pressure increases, and the C/W foams become very stable. For branched surfactants with propylene oxide middle groups, the stabilities were markedly lower for air/water foams and decane-water emulsions. The greater stability of the C/W foams to coalescence may be attributed to a smaller capillary pressure, lower drainage rates, and a sufficient surface pressure and thus limiting surface elasticity, plus small film sizes, to hinder spatial and surface density fluctuations that lead to coalescence. Unexpectedly, the foams were stable even when the surfactant favored the CO(2) phase over the water phase, in violation of Bancroft's rule. This unusual behavior is influenced by the low drainage rate, which makes Marangoni stabilization of less consequence and the strong tendency of emerging holes in the lamella to close as a result of surfactant tail flocculation in CO(2). The high distribution coefficient toward CO(2) versus water is of significant practical interest for mobility control in CO(2) sequestration and enhanced oil recovery by foam formation.

Low-temperature rapid injection NMR (RINMR) experiments were performed on two lithium reagents, n-butyllithium and 2-methoxy-6-(methoxymethyl)phenyllithium (5), with the goal of measuring the relative reactivity of the different aggregates (dimer, mixed dimer, and tetramer for n-BuLi, monomer and tetramer for 5) toward typical electrophiles. The reaction of the n-BuLi dimer with (trimethylsilyl)acetylene first forms the mixed dimer n-BuLi·Me3SiC⋮CLi, which is about 1/60 as reactive as the n-BuLi homodimer. The tetramer does not react. In the deprotonation of (phenylthio)acetylene, the n-BuLi dimer was found to be 3.5 × 108 as reactive as the tetramer, and in the addition to p-diethylaminobenzaldehyde, the relative reactivity was at least 2 × 104. In the deprotonation of (p-tolylsulfonyl)acetylene, the monomer of 5 was at least 1014 times as reactive as the tetramer. These measurements show that the difference in reactivity between the lower and higher aggregates of organolithium reagents can be many orders of magnitude higher than all previous estimates.

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