Max‐Planck Institute of Colloids and Interfaces Perspectives in Interface Research

At the end of 2016, the Max-Planck-Institute of Colloids and Interfaces (MPICI), the first MPI in the area of the former German Democratic Republic (GDR), will celebrate its 25th anniversary. It was founded after the German unification on premises of the Academy of Sciences of the GDR in Teltow and Berlin with an outstation in Freiberg (Saxony), integrating also scientists from these former institutes. After temporary management by directors from other MPIs (Professors Kahlweit, Spieß and Kompa), the founding directors M. Antonietti, R. Lipowsky and H. Möhwald took office in October/November 1993 and established new directions, deliberately not in the main stream of this area of science. The new departments on “Colloid Chemistry”, ”Theory and Biosystems” and “Interfaces” grew quite fast and the institute had already more than 300 associates in 1999, when it moved into its new building in Potsdam/Golm. With the accommodation of a 4th department “Biomaterials” under P. Fratzl in 2003 the institute had grown to its intended size of about 350 to 400 people. This size remained stable after P. Seeberger set up his department of “Biomolecular Systems” in 2008, which replaced the department “Interfaces”, that was closed in 2014 with the retirement of H. Möhwald. Overall these changes have strengthened the focus on biosystems, even though the institute continues to explore the interface between materials- and biosciences on the mesoscopic and nanoscopic length scales. Apart from playing a leading role in an emerging research field, the institute's mission has been to integrate scientists from East and West Germany and internationalize towards Europe and all over the world. One strong indicator for the success of the institute was its ranking by the Humboldt foundation which always placed it among the top three non-university institutes, although it is of comparatively small size. Still it is by far the largest in the field in terms of scientific output and promotion of young scientists. Indeed, it has always been the directors' conviction that science is best served and expanded by training young scientists, thereby creating a strong international network: More than 200 former co-workers are meanwhile professors and even more took responsibilities in positions inside or outside of science, based on their training at the institute. Needless to say that the institute's impact increased steeply during the last decade, and the number of annual citations is now above 28.000, competitive with any institute of similar size around the world. This may have been the reason, why we were approached by Advanced Materials Interfaces to arrange a special issue about work related to the MPICI. The directors supported this proposal, although only a fraction of the institute's research is devoted to interfaces and the department of interfaces no longer exists. However, it will become apparent from the content of this issue that interfaces played and play a major role in all departments of the institute, because all micro- and nanostructures in the living world and in technical materials have a large surface-to-volume ratio. We thus have invited present and former associates of all departments to contribute to this issue, and most of them agreed. Hence we apologize to those associates whom we could not invite because of space limitations or because their work had no relation with the theme of this journal, that is, materials and interfaces. This issue will cover a wide range of topics. Some of the contributions focus on structures, forces and transport at liquid interfaces (Schneck et al., Seifert et al., and Miller et al.). Understanding these aspects is most relevant to control interactions with cells (Gao et al.). Furthermore, interfacial forces can also be used to produce new structures in chemistry or biology, the main topic of the new Max Planck Research Group of K. Blank. Manipulating surfaces to enhance plasmonic interactions is in turn a topic of my ongoing cooperation with Jilin University (Zhang et al.). Interfacial interactions are also relevant for liquid films, in particular, if these films are very thin. There is still an urgent need to understand the mechanisms for the layer-by-layer assembly into multilayers, which once was a central theme of the interface department and for which biopolymeric multilayers are most relevant (Schönhoff et al.). This work is expanding into different directions: Manipulating the multilayers e.g., by thermal annealing or by adding metallosupramolecular interactions to control their interaction with cells (Moya et al., Kurth et al.). Another approach is to couple these multilayers with inorganic surfaces to control their interactions, in the special case light induced interactions (Skorb et al.). In the context of materials science one can also take a biomimetic approach, in which a conducting polymeric film is coupled with a biological photosynthetic reaction center to fabricate a bioelectrochemical cell (J.B. Li et al.). There has been an extensive activity in the institute to prepare microcapsules by depositing a well-defined film on a sacrificial template. This led to hollow capsules with a variety of applications studied in cooperation with partners. These concerned applications in corrosion protection (Shchukin et al.), improvement of surfaces (Sukhorukov et al.) or light triggered release (Skirtach et al.). It led to hierarchically organized films with internal compartments (Fery et al.). The traditional encapsulation system of liposomes is still most interesting, providing means to study a plethora of interactions in cell biology (budding, tubule formation) and in materials science (wetting) (Dimova et al.). A most interesting process to prepare capsules has been by poly­merization at oil/water interfaces (Landfester et al.) or by arranging particles at interfaces in Pickering emulsions. In the latter case these particles were halloysites, inorganic nanotubes, that have interesting properties because of their tubular geometry and provide further perspectives, because they can be filled with reaction partners, e.g. in phase transfer catalysis or for bacterial activities (Lvov et al.). There has been much success in understanding and controlling the fabrication and the organization of nanoparticles in hierarchical structures, including the discovery of new modes of organization (Cölfen et al.), and even for a traditional system such as CaCO3 there is much to uncover to understand the formation of different phases and morphologies starting with the phase diagram of solutions (Fratzl et al.). Controlling the interactions between nanoparticles can lead to new birefringent materials (Wagermaier et al.) or to new types of electrochemical cells (Shalom et al.). On the side of bioorganic molecules the organization of peptides is most promising, as it may lead to tunable and flexible light harvesting systems (Yan et al.). These can also be coupled with polymers, which lend these materials additional strength (Börner et al.) or mechanical properties (Yuan et al.). Theoretically the formation of elongated particles is most appealing in view of the creation of more interface, practically this may lead to systems with higher interfacial activity as known for patchy particles (Weikl et al.). Many biomaterials derive their function from the organic/inorganic interactions. This is demonstrated in work considering the atomic level (Zolotoyabko et al.) or at the protein and peptide level (Harrington et al., Faivre et al.) Salts have a dramatic influence on biocomposites like wood (Bertinetti et al., Burgert et al.), and this has been studied in detail from a fundamental and from an applied perspective. Overall this issue should demonstrate that the field has been expanding and diversified, has generated a wealth of knowledge, and promoted many careers, that will further drive it. We thank our present and former co-workers for their invaluable contributions and hope that readers will find an occasion to visit the MPICI in Potsdam.