UC Berkeley

Polymer nanocomposites are an extremely versatile class of materials due to the variety of materials that can be used and their many applications. Structured nanocomposites are of particular interest due to the potential of a structure/function relationship. In order to establish such a relationship, a variety of nanoscale structures with control over how to generate them. Block copolymer (BCP)-based supramolecules have been studied for the past two decades in thin film due to their ability to self-assemble to form order on the nanoscale. The complexity of supramolecules is obvious: they are constructed from noncovalently attaching a small molecule to a BCP block. As a multicomponent system, the self-assembly process is governed by competing thermodynamic and kinetic considerations. The thermodynamics that lead to equilibrium structures are well understood. In order to move beyond known structures and create tunable thin films, the kinetic pathway must studied.

The effect of several parameters in the multicomponent system on the final film structure and long-range order was quantified to understand the synergistic effects of the components. A multi-dimension diagram of the assembly process was developed that accounts for experimental observations in supramolecular thin films in the last decades from multiple groups. This diagram was used to create a design framework that can be used to control the long-range order in nanocomposite thin films by controlling the kinetic pathway.

The framework determined was applied to lithographically patterned substrates to achieve assemblies under incommensurate conditions that aligned with circular patterns. The resultant structures arise from the kinetic pathway during assembly rather than purely thermodynamic considerations.

A different kinetic regime was explored by using high molecular weight-based supramolecules. These films have two distinct kinetic regimes: slow diffusion of highly entangled polymers and the relatively faster diffusion of nanoparticles. The two regimes can be modulated so that films with different structure and feature sizes can be achieved. In situ grazing-incidence transmission small angle X-ray scattering studies were performed to monitor the kinetic pathway taken during self-assembly to quantify the changes to structure and order in a solution-based process. The information about the importance of the kinetic pathway on a multicomponent system yielded a deeper understanding of the assembly process that opens the door to creating designer nanocomposites with precisely tailorable features.