Multifunctional Nano Architectures by Spontaneous and Directed Self-Assembly: Biomimetics, Ultra-Strong Composites, and Nanoparticle Supercrystals”
In the first part of my talk I will summarize my Ph.D. research on development of layerby-layer (LBL) assembled nanostructured composites. The LBL technique is a simple method of sequential deposition of oppositely charged species, e.g. polyelectrolytes, nanoparticles, biomolecules, and even whole cells, with nanometer-scale precision. Because of its versatility and robustness, the technique has grown into an area of research with exceptional breadth of applicability, ranging from catalysis and drug delivery, to batteries and ultra-strong composites. In this respect, I will first present preparation of biomimetic clay nanocomposites having recordhigh mechanical properties. (Podsiadlo et al., Science 2007) Understanding of nanoscale mechanics and achieving efficient interfacial interactions between the inorganic nanomaterial and organic polymer matrix are key elements for successfully transferring the exceptional nanosacle properties to macroscale structures. Furthermore, I will discuss the first preparation of nanostructured LBL materials from cellulose nanocrystals possessing high mechanical, antireflective, and cell-guiding properties. In the second part of my talk, I will present my current research on characterization of collective properties in self-assembled nanoparticle (NP) superlattices (SL). In these novel architectures, NPs self-organize into crystal-like structures analogous to ionic crystals. Precise positioning of the NPs in single, binary, and even ternary assemblies leads to novel collective optical, electronic, magnetic, and even mechanical properties. The ability of the method to combine very different NPs into precise architectures has potential to yield novel metamaterials with unique properties. I will present my results on characterization and control of SLs nucleation and growth. In particular, I will show how thermal annealing can be used for controlling interparticle distance and thus electronic coupling. The first experimental results from evaluation of the mechanical properties of 3D SLs by nanoindentation technique show truly crystalline behavior of the 3D SLs, with mechanical properties being at least 2x greater when compared to random films of the same NPs. Lastly, I will discuss results from optical and electronic studies on 3D assemblies of semiconductor NPs. We observed anomalous optical behavior in the CdSe SLs which can be attributed to different degrees of 3D organization and electronic coupling between the NPs. In the case of PbS NPs SLs, we observed enhanced electronic transport with several orders of magnitude higher conductivity in 3D SLs when compared to disordered films. The results presented here will show the unique potential and opportunities for exploration in these novel materials.