Chemical Modification of Diblock Copolymers for the Functionalization of Patchy Micelles and Their Supracolloidal Chains

김경태 서울대학교 대학원 2021 국내박사

Fabrication of complex superstructures by the self-assembly of building blocks is an emerging topic in nanoscience field. Bottom-up approaches of generating hierarchical structures have advantages of high efficiency for the synthesis of periodic structures in large scale, and wide variation of available structural pools by simple combinations of building blocks. The key issue of assembling colloidal building blocks into desired superstructure is the precise control of interaction between nanoparticles. In particular, nanoparticles designed to have directional attraction between particles with orthogonal repulsion were effective colloidal monomers which can generate chain-like superstructures. The formation of patches, which are specifically localized domains on the surface of a nanoparticle, is an effective strategy to achieve this goal. Utilizing the discrete properties of patches, the selective attraction can be induced between the patches of neighboring nanoparticles. Thus, by manipulating the number and position of patches in respect to repulsive parts on a nanoparticle, well-defined superstructures can be generated from the assemblies of patchy particles Spherical micelles of block copolymer, which have the structure consisting of core and corona, can be converted into patchy micelles. By crosslinking the core parts followed by changing the solvent polarity preferable to the core but compatible to corona, the corona parts were reorganized into patches and patchy micelles were produced. The basic structure of patchy micelle, which has two patches positioned at the opposite site and divided by the exposed core part, is identical to the building blocks of linear superstructures. Therefore, by further increasing the solvent polarity to induce attraction force between patches, patchy micelles of diblock copolymers were assembled into supracolloidal chains. The properties and structures of spherical micelles can be tuned by the characteristic properties of the block copolymers consisting of them. For example, specific functionality can be delivered into the micelle by the modification of a block. In addition, when block ratio and total molecular weight of a block copolymer were adjusted, the overall size and the corona thickness of the assembled micelle can be changed, which are related to the number and size of induced patches. Thus, it can be said that chemical modification of a block copolymer to change its characteristic properties is directly connected to the functionalization of induced patchy micelles and their assembled structures. In this dissertation, various chemical modification methods in the level of block copolymers are mainly discussed, which eventually utilized for the functionalization of spherical micelles, patchy micelles and supracolloidal chains. In the Chapter 1, research background and objectives of the conducted researches are briefly introduced. In the Chapter 2, selective modification of a core- or corona-forming block in a diblock copolymer with a fluorescent dye is demonstrated. The fluorescent properties of dyes were transferred into the functionalized patchy micelles and their supracolloidal chains, which was confirmed by the direct observation of the emission with fluorescence confocal microscopy. In the Chapter 3, a strategy of converting crew-cut micelles into hairy micelles in solution state is demonstrated. By positioning the chain transfer agents at the ends of the short corona parts, they were located on the surfaces of crew-cut micelles. The modification of the micelles was conducted through surface-initiated polymerization, resulting in the direct transformation of crew-cut micelles into hairy micelles. Since the glassy cores were not changed owing to the advantage of light-mediated polymerization at ambient temperature, the corona parts were selectively extended with this method. These researches suggested that chemical modification techniques of diblock copolymer can effectively tune the properties and structures of their micellar states, expanding their potential applications particularly for light-emitting materials and libraries of available patchy micelles. 나노 크기의 단위체를 조립하여 복합적인 초구조를 형성하는 연구는 현재 나노 과학 분야에서 각광받고 있는 연구 주제 중 하나이다. 이러한 상향식 제조 방법은 주기적으로 반복되는 구조체를 효율적으로 대량 제조하는 것이 용이하고, 다양한 단위체의 조합을 통해 형성할 수 있는 초구조의 범위를 쉽게 확장할 수 있다는 장점이 있다. 콜로이드 단위체의 조립을 통해 초구조를 형성하는 연구에 있어 가장 중요한 점은 나노 입자 간의 상호작용을 정밀하게 조절하는 것이다. 구체적인 예시로, 나노 입자 간에 방향성이 있는 인력이 작용하면서 그에 대해 수직 방향으로 반발력이 작용하게 되면 선형 초구조가 형성된다. 나노 입자 간의 인력을 제어하기 위한 효과적인 방법으로는 입자의 표면에 주변과 국소적으로 성질이 다른 부위인 패치를 형성하는 전략이 있다. 패치의 구분되는 성질을 활용하면 서로 다른 입자에 위치한 패치 사이에 선택적인 인력이 발생할 수 있다. 이를 활용하여 한 입자에서 형성되는 패치의 개수 및 위치와 입자 간에 반발력이 작용하는 부위를 적절히 조절하면 이들의 조립으로부터 다양한 형태의 초구조를 형성하는 것이 가능하다. 이중블록 공중합체의 구형 마이셀은 코어와 코로나로 구분된 구조를 가진 소프트 나노 입자로, 패치 마이셀로의 전환이 가능하다. 마이셀의 코어를 가교하고 용매의 극성도를 높여 코어 부위에는 친화적이지만 코로나 부위에는 비교적 친화적이지 않은 환경을 만들어주게 되면 코로나 부위가 재배열되며 패치가 형성된다. 이렇게 형성된 패치 마이셀에서는 두개의 패치가 서로 반대편에 위치하며 그 사이로 가교된 코어가 용매에 직접 맞닿아 있게 있는데, 이는 구조적으로 선형 초구조를 형성하는 단위체와 동등하다. 그러므로 추가적으로 용매의 극성도를 높여 패치 간에 인력을 유도하게 되면 이중블록 공중합체의 패치 마이셀들이 선형의 초콜로이드 사슬로 조립된다. 구형 마이셀의 특성과 구조는 마이셀의 형성에 사용한 이중블록 공중합체의 자체적인 성질에 따라 조절될 수 있다. 예를 들어, 특정한 기능성을 블록 공중합체의 한쪽 블록에 도입하고 마이셀을 형성하면 크 특성이 구형 마이셀로도 전사된다. 또한, 블록 공중합체의 블록비와 분자량을 조절하게 되면 코로나의 두께와 마이셀의 전체 크기를 조절할 수 있는데, 이는 형성되는 패치의 개수와 크기에 영향을 미친다. 그러므로 블록 공중합체의 특성을 변화시키는 화학적 개질에 대한 연구는 패치 마이셀과 그로부터 형성되는 초구조를 기능화하는 방법과 밀접하게 연관되어 있다. 본 학위 논문에서는 블록 공중합체의 수준에서 화학적으로 개질하는 방법론에 대해 주로 다룬다. 이는 궁극적으로 구형 마이셀, 패치 마이셀, 그리고 초콜로이드 사슬의 기능화에 응용된다. 제1장에서는 진행된 연구의 배경과 목적에 대해 간략하게 소개한다. 제2장에서는 이중블록 공중합체에서 코어 또는 코로나를 형성하는 블록을 형광체를 통해 선택적으로 개질하는 방법에 대해 설명한다. 형광체의 발광 특성은 패치 마이셀과 초콜로이드 사슬로도 그대로 전사되었으며, 이는 형광 공초점 현미경을 통해 발광을 직접 관찰하는 것으로 확인할 수 있었다. 제3장에서는 표면 개질을 통해 코로나가 짧은 마이셀을 용액상에서 바로 코로나가 긴 마이셀로 전환시키는 연구에 대해 설명한다. 짧은 코로나를 형성하는 블록의 말단부에 추가적인 중합이 가능한 작용기를 위치시켜 해당 작용기를 마이셀의 표면에 위치시켰다. 그 후, 표면 개시 중합으로 직접 마이셀의 코로나 부위를 개질하여 두께를 증가시켰다. 결과적으로 이 과정을 통해 코로나가 짧은 마이셀을 코로나가 긴 마이셀로 변환할 수 있었다. 이 과정은 빛을 매개로 한 상온 중합법을 통해 진행되어 유리 전이온도가 높은 코어가 고정되었기 때문에 코로나 부위만을 선택적으로 성장시킬 수 있었다. 이러한 연구들은 이중블록 공중합체의 화학적인 개질 방법이 효과적으로 마이셀 상태에서의 특성과 구조를 변화시킬 수 있음을 보여주어 패치 마이셀의 발광 소재로서의 응용 가능성과 생성 가능한 패치 마이셀 형태의 목록을 확장할 수 있을 것으로 기대된다.

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

정주은 포항공과대학교 일반대학원 2012 국내박사

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

Morphology of Star-Shaped Block Copolymer in Thin Film

박소영 포항공과대학교 일반대학원 2021 국내박사

Block copolymers have received great attention for their various nanostructures such as spheres, cylinders, gyroids, lamellae depending on the volume fraction of one block (f), degree of polymerization (N), Flory-Huggins segmental interaction parameter (χ), and molecular architecture of block copolymer. Nonlinear copolymers, for instance, grafted, miktoarm, comb-like, and star-shaped block copolymers showed unexpected morphology compared with linear block copolymers. Especially, the phase behavior of star-shaped block copolymers is different from that of linear block copolymers. Star-shaped block copolymer thin film showed that vertically oriented microdomains are formed without any surface modifications on various substrates. This is attributed to the entropic penalty arising from star-shaped molecular architecture which overcomes the favorable interaction between each block and air (or substrate). While the orientation of microdomains in a thin film greatly depends on various factors such as molecular weight, annealing condition, film thickness, and surface tension at the interface side, there are a few studies for investigation of the morphology and (or) orientation of star-shaped block copolymers in thin films. For the nanolithographic application of block copolymer self-assembled nanostructures, the orientation control of the microdomains in thin films on a substrate becomes very important. Therefore, controlling the morphology and (or) orientation of star-shaped block copolymers is essential to study in detail and fabricate well-ordered nanostructures on a substrate. In this thesis, I investigated how the molecular weight (M), film thickness, annealing conditions, and interface affinity affected the morphology and (or) orientation of star-shaped block copolymers consisting of polystyrene (PS) and poly(methylmethacrylate) (PMMA) blocks in thin films on various substrates. The choice of PMMA-block-PS copolymer as a model system is because this could be used for nanolithography due to easy removal of PMMA chains either by reactive ion etching or by UV irradiation followed by rinsing with acetic acid. In chapter 2, I investigated, via small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM), the effect of M on the orientation of microdomains on various substrates. I successfully synthesized, by atom transfer radical polymerizations (ATRP), six-arm star-shaped PMMA-b-PS [(PMMA-b-PS)6] with two different microdomains (lamellae and PMMA cylinders). When the M is close to the critical molecular weight (Mcrit) above which block copolymers start to microphase separate, parallel orientation of lamellae (or PMMA cylinders) was obtained. This is due to the smaller entropic penalty for the formation of parallel orientation. However, even at a small increase in M (≳ 1.5 Mcrit), thin films showed vertically oriented microdomains regardless of substrates. Thus, star-shaped block copolymers are very effective to obtain vertically oriented microdomains on versatile substrates. In chapter 3, the thin film morphology of (PMMA-b-PS)6 with the volume fraction of PS block of ~0.50 was investigated by field-emission scanning electron microscopy (FE-SEM). The surface tension difference of PS and PMMA at the air surface is easily tuned depending on the annealing temperature. When the M is small, thin-film morphology greatly depends on the surface tension at the air side, when a substrate has preferential interaction with one block. For M ≲ 1.23 Mcrit, tube-like nanostructures, instead of vertically oriented lamellae (VL) were formed at the top of the film with a near-neutral air surface. However, the PMMA layer was formed on the bottom film contacting the silicon substrate with native oxide. This is because the combination of vertical and parallel lamellae generates a huge energy penalty at the T-junction connecting these two different lamellar orientations. Tube-like nanostructures were also formed on other substrates that are preferential to one block, for instance, gold or a substrate grafted by PS brush, when the film thickness does not meet the commensurability. On the other hand, when M is much higher than Mcrit, vertical lamellae were formed throughout the entire film thickness. In chapter 4, I investigated the nanostructures of (PMMA-b-PS)6 confined in a topologically pre-patterned trench to obtain long-range ordered microdomains. One of the most important parameters of block copolymers confined in the trench is the affinity between each block and the wall of the trench. The affinity between the block and the wall was controlled by using polymer brushes or selective gold (Au) deposition on one side of the walls. When the substrate and both walls are preferential to PMMA block, VL and nanotubes coexist between the walls. Because the PMMA block prefers strongly to locate at the walls with an Al2O3 layer, VL is formed near the walls with an Al2O3 layer. Also, the tube-like nanostructures are formed because the (PMMA-b-PS)6 is confined into a selective substrate to PMMA block near the wall, while the air-side is near-neutral. Thus, VL is formed near the walls and tube-like nanostructures are formed in the middle of the trench. However, for a trench grafted with PS brushes, tube-like structures are formed with a very thin PS layer. When selective Au was deposited only on one side of the walls, I observed dual nanopatterns with different numbers of lines on each side wall and the tube-like nanostructures in the middle of the trench. The formation of nanostructures of star-shaped block copolymer thin films was not only affected by the interface of air and a substrate but also the affinity between the block and both walls. By carefully controlling the affinity between the blocks and the walls, two or more different nanopatterns were realized on a single substrate.

Structural Evolution of Block Copolymer Micelles and Micelle-Inorganic Hybrids

김세영 서울대학교 대학원 2020 국내박사

지난 수십 년간의 기초 연구를 통해 블록공중합체 마이셀(Block copolymer micelle; BCM)의 자기조립에 대한 이해가 증진되어 왔으나, 새롭게 디자인된 블록공중합체를 이용한 최근의 연구 사례들은 기존의 이론으로 설명되지 않는 구조적 및 동역학적 특성을 지니는 BCM을 선보이고 있다. 한편, 자연계에서 발견되는 단백질-무기질 복합체를 본따, 우수한 물성을 갖는 조합체나 나노복합체를 구현하기 위해 BCM을 이용하는 연구 역시 활발히 진행되고 있다. 따라서, BCM 자기조립 현상에 대한 지식과 마이셀 유래 조합체의 형성원리 간의 연관성을 깊이 있게 이해하는 것이 중요하게 되었다. 본 학위논문에서는 블록공중합체의 독특한 분자모티프가 자기조립된 마이셀의 구조와 동역학에 미치는 영향 및 BCM과 무기질 간의 상호작용에 의한 조합구조의 예시를 다룬다. 이러한 연구들을 관통하여, 정확히 제어된 나노소재를 위해 BCM의 구조변화에 대한 지식을 활용하는 것의 중요성을 강조하고자 한다. 본 학위논문의 첫 부분에서는 한 쪽 블록에 긴 플루오르알킬 곁사슬이 달린 이중블록공중합체의 마이셀 구조와 완화 동역학을 소개한다. 플루오르알킬 곁가지에 의한 “병솔(Bottlebrush)”형 사슬구조는 블록에 상당한 사슬 경도(Stiffness)를 수반하며, 블록공중합체 자기조립을 통해 불용성 용매 상에서 구형 마이셀의 내핵을 이룰 때의 플루오르알킬 사슬은 그 경도로 인해 강하게 신장(Stretching)된다. 또한, 플루오르알킬 사슬의 길이에 따른 마이셀의 내핵과 코로나(Corona) 크기의 스케일링 관계식은 고전적인 열역학적 이론에서 벗어난 것으로 관찰되며, 이러한 비전형성은 불용성 병솔형 블록의 사슬 경도로부터 유래하였다. 병솔형 사슬구조의 사슬 경도로부터 유래하는 또 다른 결과는 사슬 얽힘(Entanglement)이 거의 없고 자유부피(Free volume)가 크다는 점인데, 이로 인해 병솔형 사슬은 선형 사슬에 비해 신속한 동역학적 특성을 보이며 내핵 내부에서의 완화(Relaxation) 역시 빠르다. 따라서, 본 병솔형 블록공중합체 시스템의 평형 이동 시간은 매우 신속하여 짧은 시간 안에 균일한 BCM을 제작할 수 있다. 단차맞춤(Contrast-matched) 소각 중성자 산란기법을 이용해 완화 동역학을 정량적으로 측정한 결과, 실제로 병솔형 사슬이 내핵을 이루는 BCM의 사슬 교환이 빠름을 확인하였다. 이를 통해, 병솔형 사슬이 내핵을 이루는 자기조립체는 그 구조적 거동과 완화 동역학이 신축성 있는 선형 블록공중합체의 그것과 매우 상이함을 확인하였다. 두 번째 부분에서는 BCM을 수반한 조합구조의 예시로 BCM과 광물(Mineral) 결정의 자연모사 나노복합체를 소개한다. BCM은 정전기적 상호작용을 통해 무기질의 표면에 흡착하며, 흡착된 BCM은 나아가 성장하는 광물 결정 내부에 함입될 수 있고, 이렇게 유기질이 함입된 광물은 함입 밀도에 따라 파쇄강도(Fracture Toughness)가 증강된다. BCM의 코로나 전하 밀도에 의해 BCM 흡착 세기가 달라지는 한편, BCM의 브라운확산은 성장 중인 광물 결정과의 충돌빈도에 영향을 미친다. 따라서, pH와 BCM의 수동역학적(Hydrodynamic) 크기를 조절함에 따라, 결정은 흡착 밀도가 증가하는 순서대로 (1) 방해받지 않는 상태의 성장과 (2) 성장지점의 부분적인 봉쇄와 그로 인한 함입을 거쳐 (3) 완전한 성장 억제를 겪는다. 이러한 연구 결과는, 정밀한 구조 제어를 거친 BCM을 다층적 조합구조를 만들기 위한 단위소재로 활용할 수 있으며, 이를 통해 전례 없는 물성을 지니는 나노소재를 구현할 수 있음을 시사한다. Self-assembly of block copolymer micelles (BCMs) in selective solvents is well-understood phenomenon after decades of fundamental researches, and yet recent studies with novel block copolymer designs have demonstrated structural and dynamic behaviors of BCMs beyond the classical understanding. Simultaneously, strategies that use BCMs as building blocks for hybrid structures or nanocomposites has received great attention in a couple of decades for the purpose of extraordinary material properties, mimicking the protein-inorganic hybrids ubiquitous in nature. Therefore, it is essential to make connections between the fundamentals of BCM assembly and the design principles of hybrid structures involving BCMs. This dissertation addresses impact of a distinct molecular motif at block copolymers on the structures and dynamics of self-assembled micelles and an illustrative hybrid structure made from the interactions between BCMs and inorganic materials. The underlying theme across the studies is to emphasize the importance of knowledge on the structural evolution of BCMs in making precisely engineered nanomaterials. The first part of this dissertation presents characterization and interpretation of the micellar structures and the relaxation dynamics using diblock copolymers where long fluoroalkyl side-chains are attached to a specific block. The “bottlebrush” chain architecture causes large stiffness on the fluoroalkyl block, forcing it to be strongly stretched within the core of spherical micelles in a solvent selective to the non-fluoroalkyl block. Unconventional scaling relationships between sizes of the core and the corona and the length of fluoroalkyl block are found, suggesting that this notable stiffness of the core block induces deviation from the classical thermodynamic theory of BCMs. Another consequence of the bottlebrush architecture is the absence of entanglement and the abundance of free volume within the core domain, which facilitates the internal relaxation of chain within the core. As a result, equilibration of the model diblock copolymer is substantially fast, which leads to the rapid preparation of highly monodispersed BCMs. A quantitative measurement of the relaxation kinetics was made using contrast matched small-angle neutron scattering technique, which proves fast chain exchange between BCMs with bottlebrush core block. Hence, the impact of bottlebrush architecture at the core block is found to be significant in that the dependence of BCM structures on its length and the relaxation kinetics are quite different from those of linear, flexible block copolymers. The second part presents hybrid structures involving BCMs, namely, bio-mimicking nanocomposite of BCMs and mineral crystals. Herein, BCMs are allowed to adsorb at the surface of inorganic materials via electrostatic interaction. Such adsorption brings about the occlusion of BCMs in growing mineral crystals, where the occlusion density appears to be important in determining resultant toughening effect of the occluded minerals. Charge density of the corona affects the strength of the BCM adsorption at the mineral surface, whereas Brownian diffusion of BCMs affects the collision frequency at the growing mineral crystals. Thus, by controlling pH and hydrodynamic size of BCMs, the crystals experience from unperturbed growth to partial blockage of growing site (occlusion) to adsorption-induced growth inhibition in the order of increasing adsorption density. These results indicate that BCMs with precisely controlled structure could serve as versatile building blocks for hierarchical nanostructures with unprecedented mechanical properties.

Effect of Polymer Architectures on the Self-Assembly Behaviors of Block Copolymers

Kim, Ki Hyun 고려대학교 대학원 2023 국내박사

4차 산업혁명에 따른 전자제품 수요 증가 추세는 전 세계적으로 진행되고 있다.1 지난 몇년간, 전자제품에 대한 급증한 수요는 반도체 부족으로 이어졌다. 메모리 반도체와 로직 칩 분야에서는 소수의 반도체 기업만이 살아남았고 회사들은 현재 대형 실리콘 웨이퍼에서 누가 가장 작고 결함이 없는 패턴을 얻을 수 있는지를 두고 경쟁하고 있다. 지금까지의 반도체 생산에는 포토리소그래피 사용되어졌다. 그러나, 포토리소그래피는 조사된 빛의 파장으로 인해 분해능 한계를 갖는다는 점에서 한계가 있다. 이러한 본질적인 단점과 높은 비용의 부담을 극복하기 위해 과학자들과 엔지니어들은 대안적인 해결책을 찾게 되었다. 블록공중합체 리소그래피는 기존 포토리소그래피가 가지고 있는 단점을 모두 커버할 수 있는 솔루션을 제공한다. 블록공중합체 리소그래피는 칩을 제조하기 위한 나노패턴의 제조에 있어서 대체가능한 기술로서 각광받고 있다.2-4 블록공중합체 (BCP)는 2개 이상의 화학적으로 구별되는 블록이 공유결합된 고분자의 종류이다. 블록공중합체는 많은 제어/리빙 중합 기술을 사용하여 실험실에서 쉽게 합성될 수 있다. 블록 공중합체는 유리 전이 온도(Tg) 이상에서 어닐링을 하게 되면 다양한 나노 패턴을 형성할 수 있다.2-4 이러한 특성으로 인해 지난 수십 년 동안 선형 블록 공중합체에 대한 연구가 널리 연구되어 왔다. 선형 블록 공중합체를 사용하여 형성된 나노구조체는 다음과 같은 특성을 갖는다: (i) 5~70 nm의 도메인 크기를 갖는다. (ii) 라멜라, 실린더, 자이로이드, 스피어를 포함한 다양한 모폴로지가 구현될 수 있다. (iii) 다양한 고분자 재료를 사용하여 다양한 기능기를 제공할 수 있다. (iv) 저비용 및 광범위한 가용성 등 고분자 재료의 통상적인 장점을 가지고 있다. 이에 따라 포토리소그래피의 대안으로 10nm 이하의 나노구조를 만들기 위한 광범위한 연구가 진행되고 있다. 논문의 첫 부분에서, 블록공중합체의 상분리를 촉진하기 위한 새로운 접근법을 소개하였다. 특이 구조인 스타 구조 블록공중합체가 합성되었고 아키텍쳐 특성상 묶인 구조로 인해 선형 블록공중합체에 비한 엔트로피의 감소가 발생하여 자체 조립 거동이 촉진된다. 음이온 중합을 바탕으로 스타 PS-b-PLA 블록공중합체가 합성되었고, 상분리 현상을 유사한 분자량 및 부피 분율을 갖는 선형 PS-b-PLA 블록공중합체와 비교하였다. 분석 기법들을 이용하여 도메인 크기의 감소와 함께 선형 블록 공중합체에 비해 스타 블록 공중합체의 상분리 촉진 거동이 보고되었다. 블록공중합체 리소그래피가 산업에 적용되기 위해서는 박막상에서 수직 배향을 유도하고, 박막상에서 자기조립하면서 발생하는 불가피한 결함 등 극복해야 할 몇 가지 마일스톤들이 존재한다. 논문의 두 번째 부분은 표면 중화제로서의 병솔형 고분자의 응용에 대해 다루고 있다. 랜덤 공중합체 곁사슬을 갖는 병솔형 고분자를 합성하여 기존 PS-b-PMMA 및 높은 χ값을 가지는 PS-b-PMAA 선형 블록 공중합체의 표면 중화제로 사용하였다. 선형 블록공중합체와 병솔형 고분자를 혼합하고 스핀코팅을 진행하게 되면 엔트로픽적 효과로 인해 병솔형 고분자가 블록공중합체 박막의 공기와의 계면과 기판 계면을 향해 분리되도록 하였다. 랜덤공중합체 곁사슬의 비율은 샌드위치된 선형 블록 공중합체에 대한 중립 조건으로 작용하도록 세심하게 제어되어 수직 방향의 라멜라 형태로 구현을 가능케 하였다. 진행 중인 프로젝트 및 전망 섹션에서는 논문의 두번째 부분에서 소개한 개념에 대한 후속 연구와 100nm 이상의 나노패턴을 형성할 수 있는 병솔형 블록 공중합체에 대한 연구에 대한 진행상황을 소개하였다. Growing tide of demand for electronics in accordance with the 4th industrial revolution has been an ongoing trend worldwide.1 During the last decade, this rocketed demand for electronics led to shortage of semiconductors. In the field of memory semiconductors and logic chips, only a handful of semiconductor companies have survived. The remaining companies are currently competing for who can get the smallest, defectless pattern on large silicon wafers. So far, photolithography has been used for semiconductor production. However, due to wavelength of the irradiated light, conventional photolithography is limited in that it has resolution limit. This in turn sets a boundary in how low the half-pitch can reach which is usually around 10-20 nm. To overcome this inherent downside, and the burden of high cost have led scientists and engineers to look for alternative solutions. Block copolymer lithography offers a solution that can cover all the downsides that conventional photolithography lithography has. Block copolymer lithography has been in the spotlight as the replaceable technology in producing nano-patterns for manufacturing chips.2-4 Block copolymer (BCP) is a type of polymer with two or more chemically distinct blocks covalently bonded to each other. BCP can easily be synthesized in lab using many controlled/living polymerization techniques. Block copolymers can form various nanopatterns when heated above glass transition temperature (Tg).2-4 Due to this characteristic, studies into linear block copolymers have been widely researched in the past few decades. The nanostructures formed using linear block copolymers has following properties: (i) Feature sizes ranging from 5 to 70 nm. (ii) A variety of morphologies, including lamellar, cylinders, gyroids, spheres can be created. (iii) Various polymer materials can be used to provide functionality and qualities. (iv) It possesses the conventional benefits of polymeric materials, such as low cost and widespread availability. As a result, extensive research has been conducted to create sub-10 nm nano-structures as an alternative to photolithography. In the first part of the dissertation, we demonstrate a novel approach to promote the phase separation of block copolymers. Block copolymer of unique star architecture has been synthesized and due to the existing conjunction in polymer architecture, decrease in translational entropy occurs, leading to a promotion in self-assembly behavior. Synthesis of well-defined miktoarm PS-b-PLA BCPs have been done and compared their segregation behaviors with those of linear PS-b-PLA BCPs having similar molecular weights and volume fraction. Using various analytical techniques, phase promotion behaviors of miktoarm block copolymers compared to linear block copolymers along with decreased domain sizes have been reported. For block copolymer lithography to be applied in industry, there are some obstacles to overcome such as inducing perpendicular orientation on thin film and the inevitable defects that occur while being self-assembled on thin film. The second part of the dissertation covers implementing bottlebrush polymer as surface neutralizer. Bottlebrush polymers having random copolymer side chains were synthesized to be used as surface neutralizers for conventional PS-b-PMMA and high-χ PS-b-PMAA linear block copolymers. When bottlebrush polymers were blended with linear block copolymers, bottlebrush polymer’s high chain end to mid monomer ratio led to entropic effect of bottlebrush polymers to segregate towards the bottom and top surface of block copolymer thin films. The random copolymer side chain ratios were carefully controlled to act as a neutral condition to the linear block copolymers, leading to perpendicularly oriented lamellar morphologies. In the ongoing and outlook section, follow-up study of the concepts introduced in the second part of the dissertation as well as study of bottlebrush block copolymers that can form supra-100nm nanopatterns are reported.

Phase Behavior of Acid-tethered Block Copolymers Comprising Various Ionic Additives

민재민 포항공과대학교 일반대학원 2024 국내박사

Block copolymers, consisting of two or more polymer chains covalently bonded together, exhibit phase behavior due to the incompatibility between the different polymer chains. The phase behavior of block copolymers, which form various morphologies on the nanometer scale, has been theoretically and experimentally shown to be influenced by various factors such as the Flory-Huggins interaction parameter and conformational asymmetry. Recently, research has extended to the phase behavior of block copolymers including electrostatic interactions, which affect a long-range in the polymer matrix. Many studies have reported that block copolymers containing ions show complicated phase behavior compared to the neutral block copolymers. However, due to the challenges in synthesizing ion-containing block copolymers, there is a lack of experimental data, necessitating systematic studies to precisely control electrostatic interactions within block copolymers and analyze their relationship with phase behavior. In this study, I systematically control the intermolecular interactions within block copolymers by introducing various ionic additives into acid-tethered block copolymers, such as non-stoichiometric ionic liquids, mixed ionic liquids with various ratios of two different types of ionic liquids, and zwitterions. I discuss on the resulting phase behaviors of acid-tethered block copolymer comprising various ionic additives in the point of intermolecular interaction. Furthermore, since ion-containing block copolymers can be applied as electrolytes in energy storage and conversion technologies, I investigate the relationship between phase behavior and ion transport property in it. Through this, I aim to provide insights into the design of next-generation block copolymer electrolytes from the perspective of phase separation behavior. In Chapter 1, I provide an overview of the phase behavior of ion-containing block copolymers and the relationship between morphology and ionic conductivity have been studied. This chapter discusses the impact of interactions between ionic additives and block copolymers on phase separation behavior. In Chapter 2, I investigate the phase behavior of block copolymers with non-stoichiometric ionic liquids. To precisely control intermolecular interactions, non-stoichiometric ionic liquids were introduced to two distinct block copolymers tethering different acid functional moieties. Depending on the acid functional groups, interactions with the ionic liquid were different, leading to different phase behaviors and phase transitions that are difficult to explain with general phase diagrams. Consequently, the phase diagram for ion-containing block copolymers was redefined by introducing the new variable of ionic liquid composition. Through precise control of intermolecular interactions, I stabilized the A15 phase, a Frank-Kasper phase rarely reported in soft materials. The A15 phase, with its low symmetry, was stabilized by forming interfacial layers through strong interactions between acid-functional group in block copolymers and the cations of the ionic liquid. It demonstrated that the interface morphology varied with the type of acid group due to different interactions with the ionic liquid cations. The stabilized A15 phase exhibited higher ion transport property than the lamellar structure with two-dimensional connectivity, due to the three-dimensional connectivity of the ionic domains. This approach provides an insight about how controlling interactions between ionic additives and block copolymers can stabilize complicated morphology and enhance ionic conductivity. In Chapter 3, I investigate the phase behavior and ion distribution in block copolymers comprising mixed ionic liquids. By introducing ionic liquids with varying compositions, I controlled the intermolecular interactions within the block copolymer electrolytes, mediated by the interactions with acid functional groups on the block copolymers. I analyzed the resulting phase behavior and ionic conductivity. It indicates that block copolymers with strong acid group interacting with the ionic liquids exhibited higher ionic conductivity when mixed ionic liquids were introduced, compared to when a single ionic liquid was introduced. Phase behavior and dynamic secondary ion mass spectroscopy revealed that each ionic liquid preferred to localize in the center of the ionic domains or at the block copolymer interfaces. The introduction of mixed ionic liquids alleviated the formation of dead zones at the interfaces, which otherwise hinder ionic conduction. This study provides an approach to precisely control phase behavior and interfacial properties of block copolymer electrolytes by incorporating mixed ionic liquids, thereby maximizing ionic conductivity. In Chapter 4, I study the phase behavior of acid-tethered block copolymers containing zwitterions. Particularly, when zwitterions were introduced into block copolymers with specific ratio, a rarely reported superlattice morphology was obserbed. Transmission electron microscopy revealed the distribution of zwitterions within the ionic domains of the block copolymer, and infrared spectroscopy demonstrated the intermolecular interactions between the zwitterions and the acid-functional groups in the block copolymers. These results inferred that the unique phase behavior of it was originated from the interactions between the zwitterions and the acid functional groups within ionic domain of the block copolymers. Additionally, to control the interactions between the acidic functional groups of the block copolymers and the zwitterions, imidazole additives were introduced into polymer matrix. The addition of imidazole facilitated the formation of stable interaction network even at high temperature, leading to enhanced ion conduction properties and affect mechanical properties. This study presents an approach to control the complicated phase behavior of block copolymers and improve ion transport properties through the introduction of zwitterions.

Synthesis of Various Heterogeneous Poly(methyl methacrylate) Containing Systems and Their Structural Characterizations

Lee, Sang-In 부산대학교 2023 국내박사

This dissertation describes the synthesis of various heterogeneous poly(methyl methacrylate) (PMMA) containing systems and investigated those structural characterizations. Firstly, we reported the temperature dependence of Flory-Huggins interaction parameter χ (T) between BA and MMA components by analyzing SAXS measurements fitted to the random phase approximation (RPA) equations for molten PBA-b-PMMA diblock at various temperatures. It was found from the χ estimation (χ = 0.0103 + 14.76/T ) that the enthalpy contribution, χH, a measure for temperature susceptibility of χ, is 1.7 – 4.5 folds smaller for PBA-b-PMMA than that for the conventional styrene-dien-based block copolymers which has been widely used for thermoplastic elastomers. And second, we investigated the segregation behavior of a molten diblock copolymer, poly(n-butyl acrylate)-b-poly(methyl methacrylate-ran-Styrene) (PBA-b-P(MMA-r-S)), wherein styrene (S) is incorporated as a comonomer in the second block to modulate the effective interaction between homopolymer and random copolymer block. The temperature dependence of the effective interaction parameter χeff between n-butyl acrylate (BA) and the average monomer of MMA-r-S random block was evaluated from small-angle X-ray scattering (SAXS) analysis using the random phase approximation (RPA) theory. The calculated χeff, as a function of the styrene fraction in the random copolymer block, shows a good agreement with the mean-field binary interaction model. This consistency indicates that the effective interaction between component BA and the average monomer of the random copolymer block is smaller than the interactions between pure components (χBA,MMA, χBA,S). The present study suggests that the introduction of random copolymer block to block copolymer can effectively reduce the degree of incompatibility of block copolymer system without altering the constituent species, which may serve as a viable methodology in designing novel thermoplastic elastomers based on triblock or multiblock copolymers. Lastly, as one of the latest technologies using PMMA, the gloss control of super matte surface using PMMA particles was studied. For investigating the gloss control of PMMA/ABS co-extrusion sheet by cross-linked PMMA particles, six PMMA mixture samples were prepared through an extrusion process using cross-linked PMMA particles with two different sizes (13.2 μm and 17.4 μm). We investigated the effects of size and contents of cross-linked PMMA particles on the gloss and roughness of the surface of super matte PMMA/ABS co-extrusion sheet (less than 7 GU, measuring angle 60°) by using a confocal laser scanning microscope (CLSM), contact roughness tester and surface glossmeter. There was differences in the surface roughness and gloss between A-series and B-series depending on the cross-linked PMMA particle size, and the difference was also confirmed according to the sheet processing direction. We confirmed that the correlation of gloss was not only decided by the roughness effect alone but also affected by a higher presence of cross-linked particles on the surface PMMA layer with increased light scattering efficiency.

(The)effect of compatibilizer(synthesized block copolymer by anionic polymerization) on PS/LLDPE blends

최진성 漢陽大學校 1990 국내석사

Environmental Application of Amphiphilic Star Shaped Block Copolymer for Removal of Aqueous Organic Contaminants

Seung-Gun Chung 고려대학교 그린스쿨대학원 2013 국내박사

This study investigated the encapsulation and/or photocatalytic degradation of aqueous organic compounds using newly synthesized three types of star copolymers. Polystyrene-block-poly(N-isopropylacrylamide) (P-PSN) was developed as a polymeric adsorbent containing a hydrophobic core and hydrophilic shell and applied to the removal of benzene from water. The hydrophobic core of star copolymer was effective in the encapsulation of benzene. Chlorophenols can be effectively degraded at a low energy and relatively long wavelength light source (visible light) by both porphyrin-(polystyrene-b-2-dimethylaminoethyl acrylate) (P-PSD) and porphyrin-(b-2-dimethylaminoethyl acrylate) (P-PD) catalysts, however, the encapsulation of chlorophenols were insignificant. The different results of encapsulation for benzene and chlorophenols were due to relatively low molecular weight and density, which were considered to lead to easy encapsulation. The use of P-PSD showed higher efficiency of photocatalytic degradation than P-PD for chlorophenols, because of the presence of a hydrophobic block (polystyrene). This result is due to hydrophobic-hydrophobic interaction which could be enhanced the access possibility for the porphyrin core (photocatalyst). The degradation intermediates and by-products of the chlorophenols were also identified. The analysis results revealed that the degradation of highly-chlorinated phenols was more rapid than the degradation of less-chlorinated phenols, as confirmed by residual chlorinated compound and chloride ions that were released. The newly synthesized star copolymer is non-toxic to bacteria. For these reasons, the star block copolymer has the potential to be utilized for the removal of organic pollutants from sewage and wastewater.

Phase Transformations of Spherical Block Copolymer Micelles

Chen, Liwen ProQuest Dissertations & Theses Rensselaer Polytec 2019 해외박사(DDOD)

Polymorphism is ubiquitous in nearly all crystalline materials, and control of polymorphism is important to obtain material properties for target applications. Therefore, understanding how polymorphs of materials change and how to access target polymorph by controlling thermodynamic and kinetic factors is the fundamental task in materials research.Block copolymer surfactants consist of covalently connected chemically distinct polymer blocks and aggregate into micellar structures in selective solvents. Advances in the polymer chemistry enables fine-tuning of the size and chemical properties of block copolymer surfactants, which leads to fabrication of various block copolymer micelles with properties and shapes based on solid design principles. The rich structural and property variabilities of block copolymer micelles make this material class as one of the most important model systems for exploring and understanding self-assembly of nanoscale particles.Packing structures of spherical micelles prepared with poly(1,2-butadiene-b-ethylene oxide) (PB-PEO) diblock copolymers in aqueous solutions were investigated using small angle X-ray scattering (SAXS) technique. Depending on the processing conditions, the PB-PEO spherical micelles were observed self-assembling into different close-packed structures, i.e., polytypes made by stacking two-dimensional hexagonal close-packed (2D-HCP) layers of block copolymer micelles in different stacking orders.In a 12.7 wt % solution of the PB-PEO diblock copolymer (Mn = 6.8 kg/mol and the weight fraction of the PEO block wPEO = 0.71), direct dissolution of the PB-PEO diblock copolymer produced face-centered cubic (FCC) crystals of the PB-PEO micelles. The micellar FCC structures become disordered by heating to 90 °C, and rapid temperature quenching of the disordered micelle solution to three different temperature, 40 °C, 25 °C, and 0 °C, produced FCC, randomly stacked hexagonal close packing (RHCP), and hexagonal close-packing (HCP) structures, respectively. The micellar HCP and RHCP structures are stable for at least a few weeks when maintained at the quenched temperature, but heating or cooling transformed these HCP and RHCP to FCC by grain-coarsening. Careful examination of the 2D SAXS patterns reveals that the formation of HCP and RHCP structures is related to the size of crystallites. This suggests the Laplace pressure from the finite size of crystal domains is likely the origin of the formation of the non-cubic close-packed structures of block copolymer micelles. As the crystal grains grow, the Laplace pressure becomes weak, and the micelles on close-packed lattices transform into the most stable close-packed structures: FCC.In a 23 wt % PB-PEO solution, careful thermal treatments lead to discover martensitic transformations of shear-aligned FCC crystallites of block copolymer micelles to HCP structures. It occurs by selectively sliding one specific set of 2D-HCP layers in the shear-aligned FCC crystallites among other equally possible layers. Consideration of the morphology of the shear-aligned FCC crystallites suggests that the selective martensitic shear transformation originates from different areas of available 2D-HCP layers for the martensitic shear transformation: the transformation chooses the 2D-HCP layers with the lowest sliding area, i.e., lowest frictional kinetic energy barrier.Both thermally induced diffusive and diffusionless transformations of model block copolymer micelles suggest that the size of crystal domains is a critical factor in the polymorphism of crystalline materials. In the diffusive nucleation and growth process, the size of crystal domains determines the type of crystal structures. In the diffusionless transformation, the size of crystal domains regulates the initiation and kinetics of diffusionless transformations. This finding stimulates further investigations of the effects of polymer concentration and cooling rates to the crystal structures of block copolymer micelles. Non-close packed structures of PB-PEO micelles are observed from the solutions with the tetrahydrofuran co-solvent, which is a non-selective solvent for both PB and PEO blocks.This thesis work reveals the importance of the size of crystal domains to the crystal structures and transformation kinetics and provides new understanding.