- 學位論文
嵌段共聚物奈米薄膜之微結構取向與大範圍有序化及其應用
Controlled Orientation and Long-Range Ordering of Nanostructured Block Copolymer Thin Films and Their Applications
摘要
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, controlling the orientation of self-assembled nanostructures is essential. In this study, we present a new method for forming well-ordered and oriented nanostructured thin films on Si wafer with a functionalized SiO2 surface, using homopolymers with hydroxyl group at the chain end to functionalize SiO2 surface, to give neutral substrate for the self-assembly of BCPs. To demonstrate the feasibility of suggested approaches, a series of degradable BCPs, polystyrene-b-poly(L-lactide) (PS-PLLA) with hexagonally packed cylinder and double gyroid phases, are used as model systems for creating nanostructured thin films with controlled orientation and long-range order of BCP nanostructures. In contrast to the use of random BCPs, a neutral substrate is formed by functionalizing a SiO2 substrate with hydroxyl-terminated PS (PS-OH) followed by hydroxyl-terminated PLLA (PLLA-OH). Accordingly, the surface properties can be fine-tuned by controlling the ratio of grafted PS-OH to PLLA-OH without the prerequisite of the synthesis of random BCPs. Subsequently, different methods such as thermal and solvent annealing are utilized to exploit the fabricated neutral substrate resulting from the grafting of mixed PS-OH and PLLA-OH brushes for creating expected nanostructured thin films. For cylinder-forming PS-PLLA thin film, well-ordered and perpendicular PLLA cylinders in PS-PLLA thin film can be formed by using the neutral substrate for thermal annealing. Surprisingly, the orientation that is driven by the neutral substrate is limited in that the effective length of orienting cylinders is less than twice the inter-domain spacing. By contrast, thermal annealing at high temperature can yield a neutral air surface, rendering perpendicular PLLA cylinders that stand sub-µm from the air surface. Consequently, the neutral substrate can be used to enable truly film-spanning perpendicular cylinders in films to be fabricated using the high-temperature thermal treatment. Most interestingly, the perpendicular cylinders can be laterally ordered by further increasing the annealing temperature to increase the mobility of the polymer chains for reoganization. By contrast, for gyroid-forming PS-PLLA thin film, the morphology remains as disorder-like texture after thermal annealing due to insufficient time for ordering. Note that degradation of PLLA will occur after long-time thermal annealing. Alternatively, long-range ordering of oriented gyroid thin films can be achieved by solvent annealing using appropriate solvents. With twice of integral gyroid lattice constant for sample thickness from swelling by solvent annealing to satisfy the criteria of commensuration, well-defined nanostructured thin films can be obtained. Interesting morphological evolution from disorder to gyroid and finally cylinder can be found while using a partially selective solvent for PS to anneal the PS-PLLA thin film. Moreover, during transition, characteristic crystallographic (211)G plane in the gyroid thin film parallel to the air surface can be observed, and will gradually transform into the (110)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. Similar morphological evolution can be found in the neutral substrate at which the PS chains on functionalized substrate will be stretched to preferentially reach the PS selective solvent while the PLLA chains will recoil from the solvent due to the effect of solvent selectivity. To acquire a thin-film sample with thermodynamically stable gyroid morphology, a non-preferential solvent should be used for solvent annealing to enable long-range ordering of gyroid thin film with the (211)G plane parallel to the air surface and also the substrate. The ability to achieve oriented PS-PLLA gyroid thin films with uniform surface opens up appealing applications in nanotechnology. For practical applications, by taking advantage of the degradable character of ester groups for PLLA blocks in PS-PLLA, nanoporous polymer thin films can be fabricated by hydrolyzing self-assembled PS-PLLA nanostructures, and then used as templates for the fabrication of nanohybrid materials with promising applications in electronic, optical, and magnetic devices. The fabrication of nanohybrids with different constituent components and structures can be achieved by using the templates for electroplating reaction. Consequently, nanostructured conductive polymers can be acquired by templated electrochemical polymerization through the combination of pulse electroplating method with the control of micro current. Similar approach can be exploited for the fabrication of PS/Au nanohybrid thin films by using Au precursors for templated electroplating.
並列摘要
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, controlling the orientation of self-assembled nanostructures is essential. In this study, we present a new method for forming well-ordered and oriented nanostructured thin films on Si wafer with a functionalized SiO2 surface, using homopolymers with hydroxyl group at the chain end to functionalize SiO2 surface, to give neutral substrate for the self-assembly of BCPs. To demonstrate the feasibility of suggested approaches, a series of degradable BCPs, polystyrene-b-poly(L-lactide) (PS-PLLA) with hexagonally packed cylinder and double gyroid phases, are used as model systems for creating nanostructured thin films with controlled orientation and long-range order of BCP nanostructures. In contrast to the use of random BCPs, a neutral substrate is formed by functionalizing a SiO2 substrate with hydroxyl-terminated PS (PS-OH) followed by hydroxyl-terminated PLLA (PLLA-OH). Accordingly, the surface properties can be fine-tuned by controlling the ratio of grafted PS-OH to PLLA-OH without the prerequisite of the synthesis of random BCPs. Subsequently, different methods such as thermal and solvent annealing are utilized to exploit the fabricated neutral substrate resulting from the grafting of mixed PS-OH and PLLA-OH brushes for creating expected nanostructured thin films. For cylinder-forming PS-PLLA thin film, well-ordered and perpendicular PLLA cylinders in PS-PLLA thin film can be formed by using the neutral substrate for thermal annealing. Surprisingly, the orientation that is driven by the neutral substrate is limited in that the effective length of orienting cylinders is less than twice the inter-domain spacing. By contrast, thermal annealing at high temperature can yield a neutral air surface, rendering perpendicular PLLA cylinders that stand sub-µm from the air surface. Consequently, the neutral substrate can be used to enable truly film-spanning perpendicular cylinders in films to be fabricated using the high-temperature thermal treatment. Most interestingly, the perpendicular cylinders can be laterally ordered by further increasing the annealing temperature to increase the mobility of the polymer chains for reoganization. By contrast, for gyroid-forming PS-PLLA thin film, the morphology remains as disorder-like texture after thermal annealing due to insufficient time for ordering. Note that degradation of PLLA will occur after long-time thermal annealing. Alternatively, long-range ordering of oriented gyroid thin films can be achieved by solvent annealing using appropriate solvents. With twice of integral gyroid lattice constant for sample thickness from swelling by solvent annealing to satisfy the criteria of commensuration, well-defined nanostructured thin films can be obtained. Interesting morphological evolution from disorder to gyroid and finally cylinder can be found while using a partially selective solvent for PS to anneal the PS-PLLA thin film. Moreover, during transition, characteristic crystallographic (211)G plane in the gyroid thin film parallel to the air surface can be observed, and will gradually transform into the (110)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. Similar morphological evolution can be found in the neutral substrate at which the PS chains on functionalized substrate will be stretched to preferentially reach the PS selective solvent while the PLLA chains will recoil from the solvent due to the effect of solvent selectivity. To acquire a thin-film sample with thermodynamically stable gyroid morphology, a non-preferential solvent should be used for solvent annealing to enable long-range ordering of gyroid thin film with the (211)G plane parallel to the air surface and also the substrate. The ability to achieve oriented PS-PLLA gyroid thin films with uniform surface opens up appealing applications in nanotechnology. For practical applications, by taking advantage of the degradable character of ester groups for PLLA blocks in PS-PLLA, nanoporous polymer thin films can be fabricated by hydrolyzing self-assembled PS-PLLA nanostructures, and then used as templates for the fabrication of nanohybrid materials with promising applications in electronic, optical, and magnetic devices. The fabrication of nanohybrids with different constituent components and structures can be achieved by using the templates for electroplating reaction. Consequently, nanostructured conductive polymers can be acquired by templated electrochemical polymerization through the combination of pulse electroplating method with the control of micro current. Similar approach can be exploited for the fabrication of PS/Au nanohybrid thin films by using Au precursors for templated electroplating.
並列關鍵字
無資料參考文獻
延伸閱讀
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