Copolymers of a fluorinated acrylate and styrene were synthesized to enhance the viscosity of liquid carbon dioxide. The phase behavior of mixtures of these polymers with carbon dioxide was measured at 295 K and pressures from 6.70 to 48.28 MPa. Miscibility pressures decreased with a decrease in the styrene content and increased as molecular weight increased. These polymers were also found to significantly enhance the viscosity of carbon dioxide, by a factor of ca. 5 to 400 at concentrations from 1 to 5 wt %. The optimal composition for viscosity enhancement was 29 mol % styrene-71 mol % fluoroacrylate.
The impact of various Lewis bases on the miscibility of siloxane polymers in CO 2 was investigated using both ab initio calculations and experimental phase behavior studies. A series of sidechain functional silicones were synthesized containing various Lewis bases in the side chain, and their phase behavior was compared in CO 2 at 295 K. Calculations showed that interactions between CO 2 and ethers (either a dialkyl ether or the ether oxygen in an ester group) should be as favorable as interactions between CO 2 and a carbonyl oxygen. Indeed, phase behavior results seemed to support this, as ether-functional silicones exhibited miscibility pressures as low or lower than acetate-functional analogues. Further, a keto-functional material was not nearly as CO 2 -philic as the acetate functional analogue. In general, the location of the phase boundary in CO 2 is governed by a balance between forces working to increase miscibility pressures, such as increased cohesive energy density of the polymer or factors suppressing the entropy of mixing, and those working to lower miscibility pressures, such as enhanced specific interactions with CO 2 and increased free volume or chain flexibility.
Background-Diagnosing acute coronary syndrome in patients presenting with chest discomfort is a challenge. Because acute myocardial ischemia/reperfusion is associated with endothelial upregulation of leukocyte adhesion molecules, which persist even after ischemia has resolved, we hypothesized that microbubbles designed to adhere to endothelial selectins would permit echocardiographic identification of recently ischemic myocardium. Methods and Results-Lipid microbubbles (diameter, 3.3Ϯ1.7 m) were synthesized. The selectin ligand sialyl Lewis
Compounds with strong thermodynamic affinity for carbon dioxide (CO(2)) have been designed and synthesized that dissolve in CO(2), then associate to form gels. Upon removal of the CO(2), these gels produced free-standing foams with cells with an average diameter smaller than 1 micrometer and a bulk density reduction of 97 percent relative to the parent material.
The cloud point curves of a series of oxygen-containing polymers in CO 2 were measured to attempt to deduce the effect of oxygen functional groups within a polymer on the polymer/CO 2 phase behavior. The addition of an ether oxygen to a hydrocarbon polymer, either in the backbone or the side chain, enhances "CO 2philicity" by providing sites for specific interactions with CO 2 as well as by enhancing the entropy of mixing by creating more flexible chains with higher free volume. Ab initio calculations show that both ether and ester oxygens provide very attractive interaction sites for CO 2 molecules. The binding energy for an isolated ether oxygen with CO 2 is larger in magnitude than that for a carbonyl oxygen/CO 2 complex. However, acetate functionalized polymers are more CO 2 -soluble than polymers with only ether functionalitiesspossibly because acetate functional groups contain a total of three binding modes for CO 2 interactions, compared with only one for the ether functional group. Experiments clearly indicate that adding a single methylene group as a spacer between a polymer backbone and either an ether or acetate group exhibits a strong deleterious effect on phase behavior. This effect cannot be explained from our ab initio calculations.
The effect of calcium hydroxide (Ca(OH) 2 ) on the stability of calcium carbonate (CaCO 3 ) particles was investigated with respect to the surface potential and particle size. Both CaCO 3 and Ca(OH) 2 were dissolved in ultrapure water at concentrations up to 100 mM. The solubility limits were about 18 mM for Ca(OH) 2 and about 0.13 mM for CaCO 3 at 23°C in water. Dissolution of commercial CaCO 3 in 10 mM of Ca(OH) 2 solution and dissolution of Ca(OH) 2 in 10 mM of CaCO 3 slurry were also studied at similar conditions. Conductivity, pH, zeta potential, and average particle sizes were measured for each solution. The morphological characteristics of the particles were analyzed by the SEM images. It was found that the zeta potential of CaCO 3 particles was greater than +30 mV when they were placed in the Ca(OH) 2 solution compared to a zeta potential value of −10 mV in water. It was concluded that the Ca(OH) 2 solution is a stabilizer for the CaCO 3 particles.
a b s t r a c tThere is a need to develop new, non-fluorous polymers that are highly soluble in CO 2 . Experimental evidence indicates that tertiary amine and pyridine groups may exhibit favorable Lewis acid-Lewis base type interactions with CO 2 . It is therefore reasonable to assume that incorporation of tertiary amines into the side chain or backbone of non-fluorous polymers may impart a degree of CO 2 -solubility to the polymer. We present experimental results for eight different tert-amine-containing polymers. Of these polymers, only propyl dimethylamine-functionalized poly(dimethylsiloxane) is soluble in CO 2 at temperatures and pressures accessible in our experiments, but even this polymer is less soluble than non-functionalized poly(dimethylsiloxane) at the same chain length. We have performed ab initio calculations on tertiary amine-containing moieties representative of some of the polymers examined experimentally. Our calculations confirm that amine-CO 2 interactions are indeed energetically favorable. However, we also find that the moiety self-interactions are typically more favorable than the CO 2 -moiety interactions. This indicates that the lack of solubility of amine-containing polymers in CO 2 is a direct result of strong polymer-polymer interactions.
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