Structural Investigations of Self-Assembled Nanomaterials

Controlling the self assembly of nanoparticles and block copolymers is an effective method to fine tune bulk structures in nanometer length scales. The small angle X-ray diffraction (SAXS) is the most reliable method to proof the existence of bulk morphology in nanometer length scales. In this study a custom-built instrument for measuring SAXS is designed and built by the author. The instrument is designed so that the angular resolution is comparable to small angle beamlines in the synchrotron facilities. All key functionalities are controlled from the computer. This allows programming automatic measurement series from tens of samples. Sample-to-detector distance can be adjusted from 0.5 meters up to 5 meters which allows high quality measurements of periodic structures from 1 nm beyond 300 nm. The author has used the SAXS instrument in Publications I – IV to reliably define the type of the bulk morphology of various self assembled systems. In addition, the instrument has been used in tens of other publications. In Publication I the self assembly of cowpea chlorotic mottle viruses and gold nanoparticles is demonstrated. They form an AB8fcc crystal structure that is not isostructural with any known atomic or molecular crystal structure and has previously been observed only with large colloidal polymer particles. It is shown that protein cage-guided formation of nanoparticle superlattices provides a biocompatible platform that allows the development of delivery applications and sensing applications in biological systems. In Publication II it is shown that recombinant ferritin protein cages encapsulating iron oxide and photodegradable Newkome-type dendrons self-assemble into micrometer-sized complexes with a face centered cubic superstructure. Self assembly of ABC triblock terpolymers show versatile morphologies. Certain morphologies can be used in synthesizing Janus nanoparticles. In Publication III the bulk phase behavior of polystyrene–block–polybutadiene–block–poly(tert–butyl methacrylate) triblock terpolymers is mapped. Different morphologies were identified including lamella, core-shell cylinder, cylinders in lamella interface and core-shell gyroid morphology. Versatile morphologies can be used as templates for further processing for various applications. In Publication IV the manipulation of polystyrene–block–poly(4–vinylpyridine)–block-poly(tert–butyl methacrylate) triblock terpolymer bulk morphologies through hydrogenbonding with rod-like 4–(4–pentylphenylazo)phenol is described and possibilities to fine tune the morphologies are demonstrated. Various bulk morphologies are characterized using SAXS including cylinders in lamella interface, multi layer ABCB-lamella and perforated lamella. Certain bulk morphologies can be used to produce Janus cylinders, Janus sheets and perforated Janus sheets. The perforated Janus sheets represent a "nanoporous membrane" with a pore diameter of about 20 nm and two different chemical structures on each side of the membrane. These perforated Janus sheets could be used in selective permeation applications.