Pathways toward controlled assembly of functional polymer-based nanostructures

Abstract

This thesis deals with a common drawback that is often encountered in self-assembled nanostructured soft matter. Even though spontaneous self-assembly can be used to create diverse nanostructures, the structures, as such, are typically polydomain, consisting of locally ordered small domains that lack mutual orientation and/or long range correlation. As a result, the material remains macroscopically isotropic and disordered. The aim here is to explore feasible ways, on one hand, to control the assembly and, on the other hand, to obtain macroscopically anisotropic materials and functions. We show the first example of how charge-transfer complexation between C60 fullerenes and electron-donating units of block copolymers can enable control of the morphology and properties of fullerene based materials. We also study the alignment of randomly oriented domains of nanostructured material over macroscopic length scales by using a real-time rheo-optical apparatus in combination with more detailed ex-situ structural characterization. Alignment of randomly oriented domains is not only useful for obtaining macroscopically anisotropic materials and functions but it can also be a prerequisite for detailed characterization of the local structures. This aspect is demonstrated for hierarchical liquid crystalline (LC) diblock copolymer structures which, upon inducing shear alignment, exhibit coexistence of two orthogonal orientations of the LC phase within the copolymer lamellae. Furthermore we demonstrate that ionic complexes forming a columnar LC phase can be efficiently aligned within polymer blends upon shearing, taken that the matrix polymers have sufficiently high molecular weight. This concept allows a simple route for macroscopically aligned nanocomposites with conjugated columnar LC functional additives. Finally, control of the nanoscale morphology in polymer/fullerene nanocomposite thin film devices is shown to allow tuning of the electrical switching that can enable construction of a memory unit. The working principles of such thin film organic memory devices have remained debated and the first systematic approach is here undertaken to tailor the active material composition and to study the morphology vs. functionality relationship.