Stable water-in-carbon dioxide (W/C) emulsions, for either liquid or supercritical CO2 containing up to 70 vol % water, are formed with various molecular weight perfluoropolyether ammonium carboxylate surfactants. Water droplet sizes ranging from 3 to 10 μm were determined by optical microscopy. From conductivity measurements, an inversion to C/W emulsions results from a decrease in CO2 density or salinity at constant pressure, a decrease in surfactant molecular weight, or an increase in temperature. Emulsions become more stable with a change in any of these formulation variables away from the balanced state, which increases interfacial tensions and interfacial tension gradients, enhancing Marangoni−Gibbs stabilization. This type of stability is enhanced with an increase in the molecular weight of the surfactant tails, which increases the thickness of the stabilizing films between droplets. W/C emulsions formed with the 7500 molecular weight surfactant were stable for several days.

We report new experimental data on the ability of a perfluoropolyether-based surfactant (PFPE) to form stable reverse micelles in supercritical CO 2 . Previous work from our groups showed that PFPE reverse micelles formed in CO 2 can host a wide variety of hydrophiles and even provide an environment capable of solubilizing large proteins [Johnston, K. P.; Harrison, K. L.; Clarke, M. J.; Howdle, S. M.; Heitz, M. P.; Bright, F. V.; Carlier, C.; Randolph, T. W. Science 1996, 271, 624-626].In the current work we report cloud point data for PFPE in CO 2 , X-band EPR studies, and time-resolved anisotropy measurements. The cloud point data show that a one-phase water-in-CO 2 microemulsion can be formed with a nominal molar water-to-surfactant ratio (R) of 20.7 at 45°C and 158.1 bar. EPR experiments on PFPE (with 4-hydroxy-TEMPO) and Mn-(PFPE) 2 show that PFPE aggregates in CO 2 at pressures below which a water pool can be formed. Stable Mn(PFPE) 2 micelles can also be formed in supercritical CO 2 , and the internal water pool within these micelles is able to ionize manganese, demonstrating that the water within this pool differs significantly from water within the CO 2 bulk phase. EPR results also suggest that these micelles exist in a nonspherical form. The rotational reorientation kinetics of two model fluorescent probes, rhodamine 6G and lissamine rhodamine B sulfonyl hydrazine, are described well by a biexponential decay law. The faster rotational reorientation time (φ fast ) is approximately 100 ps and remains constant regardless of CO 2 continuous phase density or R. We interpret the fluorophore rotational dynamics using three established models: a wobbling-in-a-cone model in which the fluorophore precesses about its emission transition dipole, a lateral diffusion model wherein the probe diffuses along the reverse micelle headgroup/water core interface boundary, and an anisotropic rotor model where the micelle shape itself is nonspherical.

Supported by the National Science Foundation, the GK‐12 Fellows program at the University of Colorado at Boulder explores innovative ways for engineering graduate students to use engineering as the vehicle to provide K‐12 classroom instruction and hands‐on experiences that integrate physical sciences, mathematics, engineering and technology. Engineering “Fellows” fill a crucial gap in the two‐way exchange of content and pedagogy between the College of Engineering and Applied Science and the K‐12 community of learners. The active presence of real world, engineering role models in K‐12 classrooms improves the quality of math and science content, and introduces engineering to teachers and young students as a potential career path. Working through the University's graduate program legitimizes K‐12 outreach as a valid, and satisfying, academic endeavor for graduate students.

Motivated by a desire to excite K‐12 students about the joys of engineering and spark their interest in pre‐engineering subjects, the Integrated Teaching and Learning (ITL) Program at the University of Colorado at Boulder has developed a pre‐engineering outreach program targeted at K‐12 teachers and students. To supplement anecdotal success indicators, ITL developed several assessment tools to measure the impact of these programs. Assessment strategies consist of three key components: 1) assessment of workshop participant feedback (teachers and students), 2) assessment of long‐term outcomes (teachers), and 3) assessment tools developed for the teachers' classroom use (i.e., embedded assessment). This paper reviews the process used to develop the assessment plans and tools. Examples of the tools used to assess participant feedback and preliminary outcomes are provided. Additionally, the process used to develop embedded assessment tools is described, including development of performance criteria and assessment tools that are linked to the learning goals, objectives, and K‐12 State educational standards.

liquid solvents and supercritical carbon dioxide using electron paramagnetic resonance spectroscopy. We find that rotational correlation times in the CO 2 were considerably larger than those predicted by Stokes-Einstein-Debye theory at regions close to the critical density, a finding similar to that of Heitz and Bright. Local density augmentation was quantified using a model developed by Anderton and Kauffman. At low bulk densities, we find extraordinarily high local density enhancements, with local densities over four times higher than those of the bulk, while at higher bulk densities, the apparent local density approaches that of the bulk. Although consistent with the results reported by Heitz and Bright, apparent local densities far surpassed those of the liquid solvents, a physically unreasonable result. When local densities are calculated using a molecular dynamics approach, the enhancement is less than that shown experimentally and compares reasonably to liquid densities. A clear maximum for this enhancement at subcritical densities is shown for the first time in these types of simulations. Reaction rate constants for Heisenberg spin exchange from experiments are found to be consistently higher than those predicted by theory, indicating a likely contribution of solutesolute local density enhancements to the observed slowing of molecular rotation in supercritical CO 2 .