Heterogeneously Charged Colloids for Materials Design

Materials with specific symmetries at the micro- and nano-scale level are heavily sought after because of the broad spectrum of their technological applications: three-dimensional periodic structures are known to have particular electronic and/or optical properties; ordered mono- and bi-layers are of paramount relevance for, e.g., antireflection coatings, biosensors, and photovoltaic devices; disordered responsive architectures can be used in biomedical applications where the self-healing ability and control over the connectivity are crucial. Scientists have to thus deal with the challenge of developing solid, efficient and possibly cheap methods to produce target structures with precise architectures and physical properties. Nowadays, rather than relying on externally-controlled tools, many fabrication methods are based on the self-assembly of carefully chosen/synthesized base units. Self-assembly - the spontaneous organization of microscopic units into mesoscopic structures - is a fundamental mechanism that occurs in nature at the atomic/molecular scale and is nowadays exploited in materials science at the colloidal scale: information imparted to the building units should be able to govern the spontaneous organization of such colloids into hierarchical structures and ultimately into the desired material. The macroscopic counterpart would correspond to building a tower, a castle or a bridge just by choosing the appropriate bricks and letting them self-organize into the desired structure. The newest and most successful route to self-assemble functional materials rests on anisotropic effective interactions between appropriately synthesized colloids. Over the past decade, investigations have focused on the possibilities offered to rational materials design by complex colloidal particles characterized by non-spherical shapes and/or chemical/physical surface patterns. The project we put forward focuses on a novel class of anisotropically interacting colloids: particles with differently charged surface regions. I aim at developing a novel strategy to steer - in a reliable and reversible manner - the self- assembly of bulk equilibrium structures that are ultimately responsive to external stimuli. Our aim is to specifically target ordered structures with non close-packed architectures. In this respect, we need to address (i) the minimal particle design that is able to guarantee both the experimental synthesis of the particles and the compatibility of the base units with the structures of interest, and (ii) the conditions that favor the spontaneous assembly of these units into the target architecture. Additionally, I aim to fine tune the properties of the resulting bulk material via experimentally accessible parameters, in view of possible technological applications as, e.g., data storage devices, filters, high-surface-area catalysts, lubricants and photoconductors.