Block Copolymer Self-Assembly Under Confinement

4 Block Copolymer Self-Assembly Under Confinement 

These results represent solid evidence for a general mechanism governing the phase behavior at surfaces and in thin films of modulated phases The interplay 

---

Recently, researchers paid more attention to the guided self-assembly of block copolymer thin films on a patterned surface. The patterned surface means the surface of a constrained situation is chemically or physically modified to form a pattern with specific property and size. A series of exquisite structures are found in the microphase separation of block copolymer under the patterned surface. In the theoretic work of Wu and Dzenis [43], they designed two kinds of patterned surface to direct the block copolymer self-assembly (Fig. 15.7). The self-assembled structures are found strongly influenced by the commensurability of polymer bulk period and pattern period. With mismatched patterns on two surfaces, both MC simulation [44] and SCFT researching [45] predicted the titled lamellae and perforated lamellae structures for symmetric diblock copolymers. Petrus et al. carried out a detailed investigation on the microphase separation of symmetric and asymmetric diblock copolymers confined between two planar surfaces using DPD simulation [46,47]. It is found that various nonbulk nanostructures can be fabricated by the nanopatterns on the surfaces. 

DDFT, which was developed by Fraaije et al. in 1997, is a field-based theoretical method for studying complex fluids, their kinetics and their equilibrium structures at micrometer length and microsecond time scales. DDFT has been applied to the study of the self-assembly of block copolymers in bulk, under shear and in confinement, " and to study polymer blend compatibility. Compared to the DPD method, DDFT is computationally extremely fast since larger elements can be modelled. Moreover, since the fiuid elements can freely penetrate, larger time steps can be used, and furthermore it is less likely to become trapped in a local minimum. Since DPD is a particle-based method, it can provide somewhat more detailed structural information. Nonetheless, they are both powerful tools in simulating phase separated phenomena that occurs at the mesoscale and the consistency of results from the two methods for the same coarse-grain model is evaluated in this work. 

This chapter is stmrtured as follows. A brief review on experimental and theoretical studies of block copolymers under different confinements is first presented in Section 7.04.2, including a discussion on the main features of the confining environments. Section 7.04.3 summarizes the basic principles of stmcture formation from block copolymers tmder confinement, together with relevant examples. Finally, Section 7.04.4 sets out the main conclusions from previous experimental and theoretical studies and proposes some possible future directions of research in the self-assembly of block copolymers under confinement. 

In summary, recent experimental, theoretical, and simulation studies have demonstrated that block copolymers under confinement can be used to engineer novel and complex structures with length scales at the nanoscopic range. A plethora of novel and complex morphologies have been observed in experiments. An even richer array of self-assembled structures from block copolymers under confinement has been predicted by simulations and theoretical studies. Most of these morphologies are not found in bulk block copolymers thus, confinement provides a unique and cost-effective method to produce nanostmctures. 

Dr. Baohui Li is a professor of physics at the School of Physics, Nankai University, Tianjin, China. She studied at Nankai University, where she received her PhD in 1994 in the field of condensed matter physics. She has been a Acuity member at Nankai University since 1994. Her research focuses on molmilar modeling of complex block copolymer systems, particularly in the self-assembly, phases and phase transitions of block copolymers under confinement and block copolymer solutions, as well as conformations and the related phase transitions of polyelectrolytes. 

---