The fabrication of nanostructured thin films from the self-assembly of degradable block copolymers (BCPs) has attracted extensive attention in the past decade, and a variety of appealing applications in different research areas have been suggested by using the nanostructured thin films. To create useful BCP thin films for practical uses, controlled ordering of self-assembled nanostructures is essential. In this study, we aim to fabricate gyroid-forming thin films with controlled orientation through different solvent evaporation rates after solvent swelling a degradable BCP, polystyrene-block-poly(L-lactide) (PS-PLLA), thin film. The morphological evolution during solvent evaporation is examined, and interesting phase transitions from disorder to parallel cylinder and then perpendicular cylinder, finally gyroid can be found while using a partially selective solvent for PS to swell the PS-PLLA thin film. Moreover, during transitions, characteristic crystallographic plane of (111)G, (110)G and (211)G of the gyroid-forming thin film parallel to the air surface can be observed, and will gradually transform into the (110)G and (211)G co-existing planes, and finally transform to (211)G plane due to the preferential segregation of one block to the surface that affects the relative amount of each component on the air surface. Moreover, the phase transitions during evaporation are dependent upon the evaporation rate; by decreasing the evaporation rate, the parallel cylinders will transform directly to (211)G without the transitions to perpendicular cylinder phase and co-exist crystallographic planes of the gyroid.
Although controlled solvent evaporation is a facile approach to prepare gyroid-forming thin films, the fabrication of long-range nanostructured thin films remains challenging. It is critical to increase the grain size of gyroid-forming thin film with controlled orientation. Herein, we aim to suggest a strategy for ordering the gyroid-forming thin films with large-size monograin by using PS stabilized Au nanoparticles addressing onto the thin film through solvent swelling followed by evaporation. With the introduction of the nanoparticles, the energy barrier for the nucleation of microphase separation is largely reduced and the growth of large-size monograin might be initiated from the nanoparticles resulting from the control of the nucleation density (the amount of nanoparticles introduced).

The fabrication of nanostructured thin films from the self-assembly of degradable block copolymers (BCPs) has attracted extensive attention in the past decade, and a variety of appealing applications in different research areas have been suggested by using the nanostructured thin films. To create useful BCP thin films for practical uses, controlled ordering of self-assembled nanostructures is essential. In this study, we aim to fabricate gyroid-forming thin films with controlled orientation through different solvent evaporation rates after solvent swelling a degradable BCP, polystyrene-block-poly(L-lactide) (PS-PLLA), thin film. The morphological evolution during solvent evaporation is examined, and interesting phase transitions from disorder to parallel cylinder and then perpendicular cylinder, finally gyroid can be found while using a partially selective solvent for PS to swell the PS-PLLA thin film. Moreover, during transitions, characteristic crystallographic plane of (111)G, (110)G and (211)G of the gyroid-forming thin film parallel to the air surface can be observed, and will gradually transform into the (110)G and (211)G co-existing planes, and finally transform to (211)G plane due to the preferential segregation of one block to the surface that affects the relative amount of each component on the air surface. Moreover, the phase transitions during evaporation are dependent upon the evaporation rate; by decreasing the evaporation rate, the parallel cylinders will transform directly to (211)G without the transitions to perpendicular cylinder phase and co-exist crystallographic planes of the gyroid.
Although controlled solvent evaporation is a facile approach to prepare gyroid-forming thin films, the fabrication of long-range nanostructured thin films remains challenging. It is critical to increase the grain size of gyroid-forming thin film with controlled orientation. Herein, we aim to suggest a strategy for ordering the gyroid-forming thin films with large-size monograin by using PS stabilized Au nanoparticles addressing onto the thin film through solvent swelling followed by evaporation. With the introduction of the nanoparticles, the energy barrier for the nucleation of microphase separation is largely reduced and the growth of large-size monograin might be initiated from the nanoparticles resulting from the control of the nucleation density (the amount of nanoparticles introduced).

Abstract ................................................................................................................... I
Content ................................................................................................................. III
List of Figures ....................................................................................................... V
Chapter 1 Introduction......................................................................................... 1
1.1 Self-assembly of Block Copolymers (BCPs)............................................. 1
1.2 Self-assembly of BCP Thin Films.............................................................. 5
1.2.1 Effects of surface fields on BCP thin films ...................................... 6
1.2.1.1 Substrate effects...................................................................... 6
1.2.1.1 Air surface effects................................................................... 7
1.2.1 Confinement effects on BCP thin films............................................ 8
1.2.2 Mutual effects of substrate and confinement on BCP thin films ... 10
1.3 Nanostructured Thin Films from BCP Self-assembly.............................. 11
1.3.1 Oriented nanostructured thin films from BCP self-assembly ........ 11
1.3.1.1 Temperature gradient-induced orientation ........................... 12
1.3.1.2 Electric field-induced orientation......................................... 12
1.3.1.3 Crystallization-induced orientation ...................................... 13
1.3.1.4 Shear-induced orientation..................................................... 14
1.3.1.5 Surface-induced orientation................................................. .15
1.3.1.6 Solvent-annealing-induced orientation................................. 16
1.3.1.7 Solvent-evaporation-induced orientation ............................. 18
1.3.2 Directed self-assembly ....................................................................z0
1.3.2.1 Graphoepitaxy ...................................................................... 21
1.3.2.2 Chemical patterned surface .................................................. 23
1.3.3 Nanoporous thin films from degradable BCPs .............................. 25
1.3.3.1 Dry process ........................................................................... 25
1.3.3.2 Wet process........................................................................... 29
Chapter 2 Objectives........................................................................................... 32
Chapter 3 Experimental Methods ..................................................................... 34
II
3.1 Materials................................................................................................... 34
3.2 Experimental Section ............................................................................... 34
3.3 Instrumentation......................................................................................... 35
Chapter 4 Results and Discussions .................................................................... 37
4.1 Ordering of BCP Nanostructured Thin Films Driven by Solvent
Evaporation .............................................................................................. 37
4.1.1 Morphologies of spin-coated BCP thin films................................. 38
4.1.2 Swelling degree by Solvent Annealing .......................................... 39
4.2 Morphology Evolution Induced by Solvent Evaporation ........................ 42
4.2.1 Evolution of Surface Morphology During Solvent Evaporation ... 43
4.2.2 Origins of morphological evolution under solvent evaporation .... 45
4.2.3 Morphology Evolution as a Function of Solvent Evaporation Rate……………………………………………………………………49
4.3 Morphology Evolution Induced from Functionalized Substrate ............. 52
4.3.1 Functionalized Substrate by Homopolymer of PS and PLLA....... 52
4.3.2 Induced Orientation from Functionalized Substrate ...................... 53
4.4 Synthesis of PS Stabilized Au Nanoparticle ............................................ 55
4.4.1 Synthesis and Characterization of PS-Br ....................................... 56
4.4.2 Synthesis and Characterization of PS-SH...................................... 57
4.4.3 Synthesis and Analysis of PS Stabilized Au nanoparticle.............. 59
Chapter 5 Conclusions ........................................................................................ 61
Chapter 6 References .......................................................................................... 63

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