Self-assembly of POSS-Containing Materials Anna Kowalewska Abstract Polyhedral oligomeric silsesquioxanes (POSS) are unique nanoscale com- pounds that play a very important role in nanotechnology and materials science. The three-dimensional hybrid molecular clusters can form a range of well-defined supramolecular structures, owing to their intrinsic ability for aggregation. The orga- nization of POSS in the solid state provides a non-covalent “crystalline template” approach. Understanding the mechanisms behind the cooperative interactions in POSS-based materials allows for the tailored performance of the building blocks and is essential for the development of novel hierarchical hybrid materials. Numerous reports have been published on various aspects of POSS chemistry and technology. This chapter presents an overview of selected contributions to the field of POSS- based nanostructured materials and the phenomena operating at the nanolevel in the truly beautiful world of the self-assembling polyhedra. Keywords Polyhedral silsesquioxanes · Self-assembly · Crystal packing Interface · Templating · Surfactants · MOF · Liquid crystals · Optoelectronics Advanced materials · Biomaterials 1 Introduction Polyhedral oligomeric silsesquioxanes (POSS) are structurally well-defined, three- dimensional hybrid molecular clusters with a rigid inorganic nanocore surrounded by organic groups that can be modified to achieve the desired physicochemical proper- ties. The term silsesquioxane describes their characteristic stoichiometry, where each silicon atom (sil -) is bonded to one-and-a-half oxygen (-sesquiox-) and to a hydro- carbon moiety (-ane). Octasilsesquioxane (R 8 Si 8 O 12 ,T 8 ) is POSS molecule, with quasi-spherical geometry of the siloxane core (Scheme 1). Species with spherosilox- A. Kowalewska (B ) Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90-363 Lód´ z, Poland e-mail: anko@cbmm.lodz.pl © Springer Nature Switzerland AG 2018 S. Kalia and K. Pielichowski (eds.), Polymer/POSS Nanocomposites and Hybrid Materials, Springer Series on Polymer and Composite Materials, https://doi.org/10.1007/978-3-030-02327-0_3 45