Mesoscale Modelling of Block Copolymers under External Fields.

A remarkable feature of block copolymer systems is their ability to self-assemble into a variety of ordered structures with domain sizes in the mesoscale range. One of the open questions is the dynamics of structure formation, which can be highly dependent on external fields often present in industrial conditions, such as shear, temperature gradients and confinement, or external fields which are employed to manipulate the structure, such as electric and magnetic fields. An understanding of the external field effects and effects of architecture and composition of block copolymer systems is crucial, since these factors may have a large impact on the structure formation and consequently on the structural and physical properties of the final product. In the present thesis I have focused on the comparison of results of the existing Dynamic Self Consistent Field Theory (DSCFT) with experimental observations for specific experimental systems as well as on the prediction of generic dynamic phenomena for chosen model systems. A detailed comparison with experiments was possible due to the development of such state-of-the-art experimental techniques as dynamic Scanning Force Microscopy. We have shown that the static behavior as well as the dynamics of phase transitions under an external field is well described by the theory for a number of experimental systems. This thesis demonstrates that this symbiotic approach is valuable; the experiments validate the theoretical calculations and the calculations rationalize the experimental observations. Eventually, the method can be employed to make predictions and propose improvements for yet less understood experimental and industrial systems.UBL - phd migration 201

Phase behavior in thin films of cylinder-forming ABA block copolymers: mesoscale modeling

The phase behavior of cylinder-forming ABA block copolymers in thin films is modeled in detail using dynamic density functional theory and compared with recent experiments on polystyrene-block-polybutadiene-block-polystyrene triblock copolymers. Deviations from the bulk structure, such as wetting layer, perforated lamella, and lamella, are identified as surface reconstructions. Their stability regions are determined by an interplay between surface fields and confinement effects. Our results give evidence for a general mechanism governing the phase behavior in thin films of modulated phases.Soft Matter Chemistr

Mesoscale Modelling of Block Copolymers under External Fields.

A remarkable feature of block copolymer systems is their ability to self-assemble into a variety of ordered structures with domain sizes in the mesoscale range. One of the open questions is the dynamics of structure formation, which can be highly dependent on external fields often present in industrial conditions, such as shear, temperature gradients and confinement, or external fields which are employed to manipulate the structure, such as electric and magnetic fields. An understanding of the external field effects and effects of architecture and composition of block copolymer systems is crucial, since these factors may have a large impact on the structure formation and consequently on the structural and physical properties of the final product. In the present thesis I have focused on the comparison of results of the existing Dynamic Self Consistent Field Theory (DSCFT) with experimental observations for specific experimental systems as well as on the prediction of generic dynamic phenomena for chosen model systems. A detailed comparison with experiments was possible due to the development of such state-of-the-art experimental techniques as dynamic Scanning Force Microscopy. We have shown that the static behavior as well as the dynamics of phase transitions under an external field is well described by the theory for a number of experimental systems. This thesis demonstrates that this symbiotic approach is valuable; the experiments validate the theoretical calculations and the calculations rationalize the experimental observations. Eventually, the method can be employed to make predictions and propose improvements for yet less understood experimental and industrial systems

Role of dissimilar interfaces in thin films of cylinder-forming block copolymers

We study the effect of dissimilar interfaces on the phase behavior of cylinder forming block copolymers in thin films by means of dynamic density-functional theory. In this article, we show that dissimilarity of the interfaces induces hybrid structures. These structures appear when the surface fields at the two interfaces stabilize different surface structures and/or reconstructions. We propose a general classification of hybrid structures and give an unifying description of phase behavior of cylinder forming block copolymer films. Our results are consistent with experimental observations

Time evolution of surface relief structures in thin block copolymer films

The dynamics of early stage of terrace formation in thin supported films of cylinder forming triblock copolymers was studied both theoretically using self-consistent-field theory (DSCFT) and experimentally by in-situ scanning force microscopy (SFM). In experiment, an initially flat film of incommensurable thickness was imaged continuously, and the evolution of a vertical orientation of cylinders into a parallel one as well as the respective development of thickness gradient (terrace formation) was captured in detail. On the grounds of these experimental observations, the parameters of the computational model A3B12A3 were determined to match the structures in experiment. Both systems show excellent agreement in details of structural phase transitions and in the dynamics of the step development, suggesting that the underlying transport mechanisms are governed by diffusion. The early stage of terrace formation is characterized by the development of the step height up to 80% of its equilibrium value and associated reorientation of cylindrical domains

Diblock and triblock copolymer thin films on a substrate with controlled selectivity

Using self-consistent field theory (SCFT), morphology development in symmetric linear ABC triblock copolymer films on neutral and selective substrates has been studied, and it is compared with the triblock copolymer morphologies in bulk. In particular, the effects of the substrate preferable to B (interior) block on nanopattern formation of the copolymer films are of our central interest. Here, we report various nanopatterns with tunable square morphologies. The domain patterns are much more diverse than those parallel to the substrate with substrate selectivity for end-block or those vertical to the substrate without substrate selectivity. Furthermore, in order to figure out an economical and efficient way to fabricate useful passive pattern transfer layers, which have potential applications in microelectronic processes and ultrahigh density storage media, we propose a two-step strategy and scrutinize the conditions for generating square symmetries using cylinder-forming or lamella-forming AB diblock copolymers deposited on substrates created from ABC triblock copolymer films. It is found that a thinner film with weak incompatibility can produce square patterns.close1