1. Departments of Materials Science & Engineering and Chemical Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, Departments of Materials Science & Engineering and Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695, Air Products & Chemicals Inc., Allentown, Pennsylvania 18195, Department of Physics, Institutt for Energiteknikk, N-2007 Kjeller, Norway, and Corporate Research Division, The Procter & Gamble Company, Cincinnati, Ohio 45239