1. Departments of Materials Science & Engineering and Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695, Corporate Research Division, The Procter & Gamble Company, Cincinnati, Ohio 45239, Department of Physics, Institute for Energy Technology, N-2007 Kjeller, Norway, and Department of Condensed Matter Physics & Chemistry, Risø National Laboratory, DK-4000 Roskilde, Denmark