Intrinsic and Extrinsic Interfacial Effects on Self-Assembly of Block Copolymers under One-Dimensional Confinement

Abstract

The beauty of self-assembly is in a predictable unpredictability. Self-assembly is a journey of a disordered unstable system toward a more stable ordered system as reducing its free energy. Thus, the final state of self-assembly can be predicted by the rule of minimizing system free energy. Intrinsic and extrinsic factors governing the system free energy, however, are too myriad and complex to predict their interactive synergetic effects on the self-assembly unless otherwise thoroughly investigated. In other words, only a fundamental understanding through an exhaustive study can unveil the secret of self-assembling nature, and further, providing us a way to utilize it. This idea has been the motivation of my Ph.D. study and permeated the philosophy of constructing this thesis. Block copolymers (BCPs) are one of the fascinating soft materials owing to their ability to self-assemble into various periodic nanostructures in the length scale from few-nm to over hundreds of nm. In particular, BCP self-assembly under one-dimensionally confined states such as thin films has been numerously investigated because BCP thin films form well-defined two-dimensional nanopatterns widely exploited for bottom-up nanofabrication in the use of many applications. When BCPs self-assemble with confined in thin films, the role of interfaces in their self-assembly becomes much more significant with increasing the interface-to-volume ratio. The self-assembly of confined BCPs shows more diversified nanostructures depending on both interfaces of substrate and free surface. Consequently, a key to designing the self-assembled nanostructure of confined BCPs lies in thorough interfacial control of BCP thin films. In this thesis, interfacial effects on BCP self-assembly under one-dimensional confinement will be discussed classified into two parts of intrinsic and extrinsic interfacial effects. Chapter 1 briefly introduces the background of research, BCP self-assembly, BCP nanopatterning, and interfacial effects as a critical factor in the spatially confined BCP self-assembly. Firstly, the discussions about the extrinsic interfacial effects of applied shear stress at a free surface of films, anisotropic roughness at a substrate interface, and confinement at the air/water interface are made in chapters 2, 3, and 4, respectively. Subsequently, the intrinsic interfacial effects of a replaced and controlled irreversibly adsorbed layer in BCP thin films are discussed in chapters 5 and 6. I believe this thesis provides a general insight to understand the self-assembling nature of BCPs where the interfacial effects become critical under one-dimensional confinement. Finally, with this thesis as momentum, I hope much attention would be paid not only to the widely studied extrinsic interfacial effects but also to the relatively less studied intrinsic interfacial effects of an irreversibly adsorbed layer in BCP thin films.