ACKNOWLEDGMENTS
This work is financially supported by the Beijing Advanced Innovation
Center for Soft Matter Science and Engineering at the Beijing University
of Chemical Technology and by the Deutsche Forschungsgemeinscahft (DFG)
through the project ZE 542/12-2 within the priority program SPP 1934. We
thank Dr. Wei Wang for critical reading of the manuscript and the help
of Jinglei Nie in drawing some of the figures.