Study on the Phase Behavior of Block Copolymer Thin Film : 박막형태의 블록공중합체에서 보이는 상 거동에 관한 연구

다국어 초록 (Multilingual Abstract)

Block copolymers consist of two or more immiscible homopolymers linked
by covalent bonds, which exhibit a variety of ordered phases in nano-scale through
micro-phase separation. Lamellar (LAM), hexagonally perforated lamellar (HPL),
double gyroid (DG), hexagonally packed cylinder (HEX) and spheres arranged in
body centered cubic lattice (BCC) phases have been well investigated, and recently
Fddd phase was experimentally found.
The phase behavior of a block copolymer is typically determined by the
composition of a block copolymer and the incompatibility between blocks which is
expressed by the product of Flory-Huggins interaction parameter (χ) and degree of
polymerization. Since χ is a function of temperature, various thermal phase
transitions can occur at a certain composition. And an epitaxial relationship between
two ordered phases is usually observed during the phase transition.
The phase behavior of block copolymer thin film is different from that in
bulk because block copolymer thin films are additionally influenced by interfacial
interactions (with a substrate, free surface, or both) and the morphologies are
geometrically confined. In this dissertation study, the phase behaviors in thin film
were investigated to establish how the factors, such as film thickness and interfacial
interaction, affect the phase behavior of block copolymer.
In chapter 1, General introduction of block copolymer and phase transition
induced by changing temperature is briefly reviewed. Especially, most part is
devoted to the phase behavior of block copolymer in the form of thin film. And the
principles of grazing incidence small angle X-ray scattering (GISAXS), transmission
electron microscopy (TEM) and transmission electron microtomography (TEMT)
used for morphological characterization of thin film are described.
In chapter 2, the effect of film thickness on the phase behavior of diblock
copolymer was investigated. The phase diagram was constructed for a polystyreneblock-
polyisoprene (PS-b-PI, MW = 32,700, fPI = 0.670) in thin films on Si wafer as a
function of film thickness over the range of 150-2410 nm (7-107L0, L0: domain
spacing of HPL) and temperature. The PS-b-PI (755 nm) exhibits a variety of ordered
phases from HPL via DG to HEX before going to disordered phase (DIS) upon
heating. The morphology of the PS-b-PI in thin film was investigated by GISAXS,
TEM and TEMT. In thin film, the phase transition temperature is difficult to be
determined unequivocally with in-situ heating process since the phase transition is
slow and two phases coexist over a wide temperature range. Therefore, in an effort to
find an ‘equilibrium’ phase, we determined the long-term stable phase formed after
cooling the film from DIS phase to a target temperature and annealing for 24 hrs at
the temperature. The temperature windows of stable ordered phases are strongly
influenced by the film thickness. As the film thickness decreases, the temperature
window of layer-like structures such as HPL and HEX becomes wider whereas that
of the DG stable region decreases. For the films thinner than 160 nm (8L0), only HPL
phase was found. In the films exhibiting DG phase, HPL at the free surface was
found, which gradually converts to the internal DG structure. It seems that layer
structure which can minimize surface energy is preferred. The relief of interfacial
tension by preferential wetting appears to play an important role to control the
morphology in very thin films.
In chapter 3, the pathway of phase transition upon cooling from DIS to DG
stable region was investigated for PS-b-PI (Mn = 32,300, fPI=0.670) in thin film (755
nm thick) on silicon wafer. The transition from DIS to DG was monitored by
GISAXS, TEM and TEMT. The transition pathway was found to be affected by
quench depth and cooling rate. For a slow cooling to a shallow quench depth, the
phase transition occurred in the reverse order of heating (DIS→HEX→DG). On the
other hand, when the thin film was deep-quenched into the DG region (close to the
phase boundary of DG and HPL), a transient HPL phase was observed before the
final DG phase was formed; i.e., DIS→HEX→HPL→DG. HPL start to develop from
the interfacial regions and the transformation from HEX to HPL is verified by the 3
different orientations of HPL layers which epitaxially grows from the three sets of
{10}HEX. In the fast cooling, HPL occurs as a transient phase regardless of quench
depth. The pathway via HPL as transient was not found in bulk. It indicates that HPL
is a kinetically favored phase with respect to DG in thin film. In thin film, layer-like
structure, HPL alleviates interfacial tension due to its structure, and it leads the phase
transition pathway in the direction of forming a transient phase prior to reaching the
thermodynamic stable phase, DG.
In chapter 4, the epitaxial phase transition between DG and HEX in PS-b-PI thin
film on Si wafer was investigated. The thermal transition occurred reversibly and its
transitional structure was visualized using TEMT. The epitaxial transition of DG and
HEX is affected by the transition direction. It was shown that one epitaxy dominated
during the phase transition from DG to HEX, where the {121}DG, {111}DG and
{220}DG are converted to {100}HEX, {110}HEX and {001}HEX, respectively. Although
dimensional mismatch occurs in a lateral plane in this epitaxial relationship, all loci
have the same path and the arms parallel to film plane of DG mostly contribute to
form cylinders. When the transition starts from HEX, the other epitaxial relationship,
where {100}HEX, {110}HEX and {001}HEX are changed to {121}DG, {220}DG and
{111}DG ,respectively, was also observed. A 5-fold junction was detected at the
transitional region, supporting the transition mechanism predicted by Matsen. In this
epitaxy, two phases match in orientation and domain spacing, but cylinders are
formed through diffe

목차 (Table of Contents)

• Chapter 1. General Introduction 1
• 1.1. Block Copolymer 1
• 1.2. Block Copolymer Thin Film 5
• 1.3. Structural Characterization Techaniques 10
• 1.4. References 29
• Chapter 2. Effect of Film Thickness on the Phase Behaviors of Diblock Copolymer Thin Film 35
• 2.1. Introduction 35
• 2.2. Experimental Section 37
• 2.3. Results and Discussion 39
• 2.4. References 55
• Chapter 3. Disorder-to-Order Transition Pathway in Diblock Copolymer Thin Film 61
• 3.1. Introduction. 61
• 3.2. Experimental Section 64
• 3.3. Results and Discussion 68
• 3.4. References .81
• Chapter 4. Epitaxial Phase Transition of DG and HEX in Diblock Copolymer Thin Film 86
• 4.1. Introduction 86
• 4.2. Experimental Section 90
• 4.3. Results and Discussion 93
• 4.4. References 107
• Chapter 5. Structural Characterization of Fddd phase in Diblock Copolymer Thin Film by Electron Microtomography 113
• 5.1. Introduction 113
• 5.2. Experimental Section 116
• 5.3. Results and Discussion 119
• 5.4. References 131
• 국문 요약문 137
• 이력서 142