Cover Story
Our recent publication, which has been selected as the cover story, highlights the work of our research group.
Research
Keywords of Research Activities
Chirality, Nanonetwork, and Nanopattern
Research Topics with Represented Review Articles
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Self-assembly of chiral polymers and block copolymers
Prog. Poly. Sci. 2011, 36, 376-453.
Acc. Chem. Res. 2017, 50, 1011-1021.
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Nanonetworks from self-assembly and templated syntheses
Chem. Soc. Rev. 2015, 44, 1974-2018.
Acc. Chem. Res. 2022, 55, 2033-2042.
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Top-down and bottom-up methods for nanopatterning
Prog. Poly. Sci. 2018, 77, 19-68.
Research Highlights
From fundamentals of polymer physics and nanoscience to develop new nanomaterials and nanotechnologies for applications
Self-assembly of Chiral Block Copolymers.
Block copolymers composed of chiral entities, denoted as chiral block copolymers (BCP*s), were designed for mesochiral self-assembly. A helical phase was discovered for the first time in the self-assembly of BCPs [J. Am. Chem. Soc. 131, 18533 (2009).]. A review article entitled “Helical architectures from self-assembly of chiral polymers and block copolymers” was given to address the effect of chirality on BCP self-assembly [Prog. Polym. Sci., 36, 376 (2011).]. Homochiral evolution at different length scales in the self-assembly of the BCPs* was found [J. Am. Chem. Soc. 134, 10974 (2012).]. Generalization of the chirality effect on the self-assembly of BCPs was established [PNAS 116, 4080 (2019)]. Similar behaviors with respect to the homochiral evolution from self-assembly can also be found in crystallization of chiral polylactides [Angew. Chem. Int. Ed., 126, 4539 (2014); Angew. Chem. Int. Ed., 54, 14313 (2015).]. As a result, a methodology for the examination of chirality transfer at different length scales from mesochiral self-assembly were proposed (Figure 1) [Acc. Chem. Res., 50, 1011 (2017).]. With the helicity at the microphase-separated interface of self-assembled BCPs*, monoliths with selectivity of circular polarized light can be successfully fabricated as a device (Figure 2) [ACS Macro Lett. 6, 980 (2017). Front Cover]. Similar concept was applied to create helical superstructures, giving specific optical activities [ACS Macro Lett. 11, 1306 (2022). Front Cover]. By extending the homochiral evolution concept of mesochiral self-assembly, it is feasible to fabricate nanonetwork phase with controlled helicity from self-assembly for the first time (Figure 3) [Science Advances, 6, eabc3644 (2020)]. With a simple method for identification of network chirality developed by our team, a new concept for structuring from the self-assembly of soft matter was developed [Nature, 575, 175 (2019) R.M. (Ho is one of the coauthors)]. The new discoveries of helical phases give rise to the new opportunities for exploiting self-assembled materials as metamaterials; it can be used as chiral plasmonic devices [Adv. Optical Mater. 9, 2170036 (2021) Inside Cover Story], giving appealing approach for fabrication of chiral metamaterials from bottom-up approach.
Figure 1. Discovery of helical phase from the self-assembly of chiral block copolymers [Prog. Polym. Sci., 36, 376 (2011) IF=27.1] with proposed methodology for the examination of chirality transfer at different length scales [Acc. Chem. Res., 50, 1011 (2017). IF=18.0]
Figure 2. By taking advantage of memory effect and guest-host association for circularly polarized light device with tuning wavelength [ACS Macro Lett. 6, 980 (2017) Cover Story IF=5.8]
Figure 3. Fabrication of nanonetwork phase with controlled helicity from mesochiral self-assembly and also gyroid-structured Ni with controlled helicity [Sci. Adv., 2020, 6, eabc3644. IF=13.6].
Well-ordered nanonetwork materials.
With the formation of helical phase from self-assembled polylactide-based BCPs*, gyroid phase can be obtained by twisting and shifting mechanism via order-order transition (Figure 4) [Macromolecules, 47, 7993 (2014) Front Cover]. With the use of selective solvent for casting of polydimethylsiloxane-based BCPs, a variety of network phases including primitive, diamond and gyroid can be obtained [PNAS, 118, 11 (2021).]. By taking advantage of the characters of PLA and PDMS, nanoporous polymers with well-defined nanochannels can be fabricated after removal of nanonetwork PLA or PDMS in the BCP via hydrolysis or HF etching, and then used as templates for templated syntheses, giving the feasibility to fabricate well-ordered nanonetwork (mesoporous) materials and corresponding nanohybrid materials (Figure 5) [Chem. Soc. Rev., 44, 1974 (2015).]. As demonstrated, helical nanocomposites can be fabricated by templated sol-gel reaction [J. Am. Chem. Soc., 131, 1356 (2009)]. With the same fashion, it is possible to fabricate well-ordered nanonetwork SiO2, giving materials with characters of optical metamaterials [Nano Letters, 10, 4994 (2010)]; that can serve as antireflective structure in the visible light region [TW patent I425058; US patent 8,518,561; US Patent 8,927,437]. Currently, collaboration with Formosa Corp. for the platform technology of templated syntheses is undergoing for mass production process. Biomimicking from nature, well-ordered nanonetwork materials with optical properties similar to butterfly-like photonic crystal can be fabricated by templated sol-gel reaction (Figure 6) [Adv. Mater. 26, 3165 (2014). Front Cover], giving the optical films with high reflectance [US Patent 9,428,626 (2016)]; collaboration with Lite-On was funded by the ministry of Economics for the development of UVC LED reflective optical film. With the first-time development of templated electroless plating, well-ordered nanonetwork Au can be fabricated [Adv. Mater. 23, 3041 (2011)], giving superior surface plasmonic resonance performance [Adv. Mater. 25, 1780 (2013)]. Following similar approach, well-ordered nanonetwork Ni can be mass production; with the fabrication of micrometer-size Ni particle with nanonetwork texture, it is possible to use it as recyclable catalyst for hydrogenation [NPG Asia Mater. 11, 9 (2019). Front Cover]. With the discovery of templated condensation polymerization, well-ordered nanonetwork epoxy fabricated appears high impact properties due to its deliberate structuring [Nano Letters 21, 3355. (2021).]. Bioinspired by mantis shrimp, well-ordered hydroxyapatites fabricated by templated sol-gel reaction demonstrates the behavior of brittle to ductile transition on mechanical performance (Figure 7) [ACS Nano 16, 18298 (2022).]. Consistently, well-ordered nanonetwork calcium carbonate with high impact property can be fabricated by templated crystallization reaction; with the use of top-down approach, it is possible to create the nanonetwork structure with smaller strut size, giving mechanical performance beyond nature with superior strength and energy absorption capability than starfish (Figure 8) [ACS Nano 17, 15217 (2023). Front Cover]. Accordingly, the fabrication of mechanical metamaterials with network texture becomes feasible from self-assembly.
Figure 5. Platform technology for the fabrication of well-ordered nanohybrids and nanoporous materials through templated syntheses [Chem. Soc. Rev., 44, 1974-2018 (2015). IF=46.2]
Figure 4. By taking advantage of twisting mechanism, double gyroid phase can be effectively obtained by mesochiral self-assembly. [Macromolecules, 47, 7993 (2014). Cover Story IF=5.5]
Figure 6. Biomimicking from nature, materials with shifting networks to achieve photonic properties similar to butterfly wing structure [Adv. Mater. 26, 3165 (2014) Cover Story IF=29.4]
Figure 7. Bioinspired by mantis shrimp, well-ordered nanonetwork hydroxyapatite can be fabricated by templated sol-gel reaction, givng high impact property with mechanical metamaterial character [ACS Nano 16, 18298 (2022) IF=17.1]
Figure 8. Bioinspired by starfish, well-ordered nanonetwork calcium carbonate can be fabricated by templated crystallization reaction, givng superior mechanical performation with mechanical performance beyond nature. [ACS Nano, 17, 15217 (2023). Cover Story IF=17.1]
Nanopatterning Technologies.
By taking advantage of easy thin-film formation with precision control, the self-assembly of block copolymers is appealing for the development of nanopatterning. A variety of novel and creative applications by using degradable block copolymers for nanopatterning technologies [US Patent 7,632,544] have been successfully exploited, giving a solution-oriented research model for product developing. The technologies are applying in different research areas including drug control release [ACS Nano, 3, 2260 (2009)], nanolithography [ACS Nano, 4, 2088 (2010)] and optoelectronics [Adv. Func. Mater., 21, 2729-2736 (2011); ACS Nano, 7, 2000 (2013)]. An invited review article entitled “Silicon-Containing Block Copolymers for Lithographic Applications” was given in Progress in Polymer Science (Figure 9) [Prog. Polym. Sci., 77, 19 (2018).]. Silicon-containing BCPs is appealing in BCP lithographic technology for the applications of naon-MEMS process due to its small feature size from self-assembly and high etching selectivity. Yet, it is usually a critical problem for silicon-containing BCPs in the applications; the low surface energy will give the formation of wetting layer that creates the difficulty to give perpendicular orientation for lithographic applications. An interesting physical behavior was found recently by Ho and coworkers, there is a significant reduction on surface tension for polymer melt at which the discrepancy between the surface tensions of constituted blocks can be greatly reduced to give neutral surface, creating the perpendicular orientation of nanostructured BCP monoliths simply by thermal annealing under vacuum (Figure 10) [ACS Nano 16, 12686 (2022))]. This discovery will give the new concept for the design of nanofabrication; currently, the collaboration with TSMC for the development of 2nm technology is undergoing with creative and promising results.
Figure 9. Silicon-containing block copolymers for lithographic applications [Prog. Polym. Sci., 77, 19 (2018).]. [Prog. Polym. Sci., 77, 19 (2018). IF=27.1]
Figure 10. Discovery of vacuum effect on reduction of surface tension for polymer melt, giving neutral surface for BCP nanopatterning [ACS Nano 16, 12686 (2022). IF=17.1]