[1] Univ Fribourg, Dept Phys, CH-1700 Fribourg, Switzerland
[2] Fribourg Ctr Nanomat, CH-1700 Fribourg, Switzerland
[3] Nestle Res Ctr, CH-1000 Lausanne, Switzerland
[4] Helsinki Univ Technol, Dept Engn Phys, FIN-02150 Espoo, Finland
[5] ETH, Swiss Fed Inst Technol, Dept Mat, Inst Polymers, CH-8093 Zurich, Switzerland
[6] Univ Calif Santa Barbara, Mat Res Lab, Santa Barbara, CA 93106 USA