COLL 596 |
| Carboxylic acid groups are an important functional group in the environment. The thermodynamic properties of carboxylic acid moieties are of interest because they can control transport through soils by binding species at the mineral-water interface. Using second harmonic generation, we measured interfacial pKa values, protonation states, surface free energy densities, surface charge densities, and surface potentials for a monoprotic carboxylic acid functionalized silica/water interface. We observe two pKa values: one at 9(1), which is consistent with a lateral hydrogen-bond stabilized network, and one at 5.6(2), which is similar to pKa values of monoprotic organic acids in solution. Between pH 2 to pH 12, the interfacial potential changes over 3 orders of magnitude, from 10-2 mV to several millivolts, and the interfacial energy density changes by 7 orders of magnitude, from 10-7 mJ/m2 to several mJ/m2. Also presented are complementary sum frequency generation studies to characterize the interface. |
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Surface Chemistry Symposium in Honor of Gabor Somorjai
2:00 PM-5:20 PM, Thursday, 14 September 2006 Sir Francis Drake -- Franciscan Room, Oral
Division of Colloid & Surface Chemistry |