Research Highlights in Recent Years

Self-assembly of Chiral Block Copolymers.

Block copolymers comprising chiral entities, denoted as chiral block copolymers (BCPs), were designed to fabricate helical architectures from self-assembly [R.-M. Ho et al. “Helical architectures from self-assembly of chiral polymers and block copolymers” Prog. Polym. Sci., 36, 376-453 (2011). SCI Impact Factor~26]. A helical phase (denoted H to distinguish its P622 symmetry from that of the normal hexagonally packed cylinder phase, denoted H with P6/mmm symmetry) was discovered in the self-assembly of polystyrene-b-poly(L-lactide) (PS-PLLA) BCPs* [J. Am. Chem. Soc., 131, 18533 (2009). SCI Impact Factor~14]. The phase behavior of the PS-PLLA BCPs* was systematic examined. Also, the mechanisms of chiral transfer at various length scales in the self-assembly of enantiomeric chiral block copolymers (BCPs) were studied. The evolution of homochirality from molecular chirality into phase chirality in the self-assembly of the BCPs was found [J. Am. Chem. Soc., 134, 10974 (2012).]. The operation of the self-assembly of the BCP* may provide insights into morphological evolution from the molecular level via homochiral evolution, and give the appealing applications such as chiral metamaterials. Similar behaviors with respect to the evolution of homochirality can also be found in crystallization of chiral polylactides [Angew. Chem. Int. Ed., 126, 4539 (2014); Angew. Chem. Int. Ed., 54, 14313 (2015). SCI Impact Factor~12]. As a result, methodologies for the understanding of the mechanisms of the chirality transfer at different length scales in the self-assembly of chiral homopolymers and block copolymers were proposed to provide the approaches to give supplementary information for disclosing the mysteries of the homochiral evolution from molecular level to hierarchical superstructures [Acc. Chem. Res., 50, 1011 (2017). SCI Impact Factor~20 (Figure 1)].

Figure 1 Schematic illustration of the chirality transfer from molecular chirality to hierarchical chirality for chiral homopolymers and chiral block copolymers, and the methodologies for the examination of chiral structures at different length scales [Acc. Chem. Res., 50, 1011 (2017).]

Moreover, we demonstration that the induced chirality of an achiral chromophoric dye as a joint of polylactide-containing chiral block copolymers (BCPs) can be driven by self-assembly, giving the achiral dyes preferentially arranged in a one-handed helical array at the microphase-separated interface. This helical arrangement of the achiral dyes can be memorized after hydrolysis of the polylactides in the BCPs, and serves as a chiral template for further chirality induction of different achiral dyes possibly through attractive aromatic π-π interactions at the interface, producing nanostructured chiral materials with tunable circular dichroism signals at desired wavelengths [ACS Macro Lett. 6, 980 (2017). Front Cover Story (Figure 2)]. Also, we suggested a facile method to acquire double gyroid (DG) phase from the self-assembly of chiral block copolymers (BCPs), polystyrene-b-poly(L-lactide)(PS−PLLA). A wide region for the formation of DG can be found in the phase diagram of the BCPs, suggesting that helical phase (H) from the self-assembly of BCPs can serve as a stepping stone for the formation of the DG due to an easy path for order-order transition from two-dimensional to three-dimensional (network) structure [Macromolecules, 47, 7993 (2014). Front Cover Story (Figure3)].

Fabrication of Nanohybrids and Nanoporous Materials from Templating of Block Copolymers.

Fabrication of Nanohybrids and Nanoporous Materials from Templating of Block Copolymers. Well-defined nanoporous polymeric materials having various nanostructures including cylinder, helix and gyroid can be fabricated by degeneration of constituted block in block copolymer (BCP), and treated as templates. Reactions such as sol-gel reaction and electroless plating can be carried out within the templates for the manufacturing of nanostructured hybrids. Well-defined nanohybrids with hexagonally packed SiO2 nanohelices embedded in a polymer matrix can be fabricated through templated sol-gel reaction [J. Am. Chem. Soc., 131, 1356 (2009).]. Also, nanoporous double gyroid SiO2 network materials with porosity over 60% can be prepared, giving extremely low-n materials for antireflection structure (Nano Letters, 10, 4994 (2010). SCI Impact Factor~12) [TW patent I425058 (2014); US patent 8,518,561 (2013); US Patent 8,927,437 (2015)].

Figure 2. By taking advantage of induced circular dichroism and memory effect, nanostructured chiral materials with tunable CD signals at desired wavelengths can be fabricated. [ACS Macro Lett. 6,980 (2017). Front cover story]

Figure 3. By taking advantage of twisting mechanism, double gyroid phase from the self- assembly of chiral block copolymer can be effectively obtained. [Macromolecules, 47,7993 (2014). Front cover story]

Moreover, we suggest a simple method for the preparation of nanomaterials with new functionality by physical displacement of a network phase, giving a change in space group symmetry and hence properties. A double gyroid structure made by the self-assembly of block copolymers is used as a model system for the demonstration of shifting networks to achieve single gyroid-like scattering properties [Adv. Mater. 26, 3165 (2014). SCI Impact Factor~20 Front cover story (Figure 4)]. As a result, free-standing single gyroid-like network materials can be fabricated to give nanophotonic properties, similar to the photonic properties of butterfly wing structure [US Patent 9,428,626 (2016)]. A collaborative project with Lite-On Corp. was built to develop the high reflectance materials in the application of UV LED. Similar approach can also be applied for templated electroless plating to create nanoporous metals such as nickel [Adv. Mater. 23, 3041 (2011). SCI Impact Factor~19] and gold [Adv. Mater. 25, 1780 (2013).]. This fabrication methods provide the feasibility for the mass production of well-ordered nanoporous metallic materials. Currently, we are working with LCY Chemical Corp. by using fabricated nanoporous Ni for the hydrogenation of thermoplastic elastomers to create high added value TPE. As a result, a platform technology to fabricate various well-defined nanohybrids and nanostructured porous materials can be established. A variety of well-defined nanohybrids with different constituted components including polymers, ceramics and metals can be created to give a “Materials Library” for practical applications in nanotechnologies [Chem. Soc. Rev., 44, 1974-2018 (2015). (SCI Impact Factor~39) (Figure 5)]。

Figure 4 Biomimicking from nature, a double gyroid structure is used as a model system for the demonstration of shifting networks to achieve single gyroid-like scattering properties, similar to the photonic properties of butterfly wing structure [Adv. Mater. 26, 3165 (2014). Front cover story].

Figure 5 Platform technology for the fabrication of well-ordered nanohybrids and nanoporous materials through templated syntheses [Chem. Soc. Rev., 44, 1974-2018 (2015)].

Nanopatterning Technologies by Integration of Top-Down and Bottom-Up Methods

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 (2009)] have been successfully exploited, giving a solution-oriented research model for product developing. The technologies are applying in different research areas including display industry [Adv. Mater. 19, 3584 (2007) SCI Impact Factor~20], drug control release [ACS Nano, 3, 2260 (2009) SCI Impact Factor~14], nanolithography [ACS Nano, 4, 2088 (2010)] and optoelectronics [Adv. Func. Mater., 21, 2729-2736 (2011) SCI Impact Factor~11; ACS Nano, 7, 2000 (2013)]. In particular, a unique silicon-containing star-block was designed and synthesized for self-assembly; by taking advantage of entropy effect, perpendicular orientation nanostructured thin films with high aspect ratio can be successfully fabricated, giving unique 2D and 3D nanopatterns [Polymer Chemistry, 8, 843 (2017) Front cover story (Figure 6)]. An invited review article entitled “Silicon-Containing Block Copolymers for Lithographic Applications” will appear in Progress in Polymer Science [Prog. Polym. Sci., DOI: 10.1016/j.progpolymsci.2017.10.002 (2017) SCI Impact Factor~26 (Figure 7)].

Figure 6 By taking advantage of the architecture effect of star-block copolymers on self-assembly, unique nanopatterns can be successfully fabricated for practical applications in nanopatterning [Polymer Chemistry, 8, 843 (2017) Front cover story].

Figure 7. Silicon-containing block copolymers for lithographic applications [, DOI: 10.1016/j.progpolymsci.2017.10.002 (2017)].

Summaries of academic performance

Over 140 peer-reviewed scientific papers, over 80 invited lecture, ten papers being cited for over 100, corresponding papers in past ten years over 75 with average IF over 9, total citation from 2013 to 2017 over 2,200, H-index ~ 40 (Google citation). With the outstanding contributions to the understanding of novel nanostructures and the fabrication of well-defined nanohybrid materials from self-assembly and templating of chiral block copolymers, Dr. Rong-Ming Ho was elected as a fellow of American Physical Society (APS) in 2014; the first scholar in Taiwan being nominated by APS Division of Polymer Physics and selected as a fellow. Dr. Rong-Ming Ho has been serving as a consultant for Industrial Technology Research Institutes to develop the STOBA technology for high-safety lithium battery materials that won the R&D 100 Award. Also, the platform technologies he developed for the fabrication of well-ordered nanohybrids and nanoporous materials are appealing in industrial applications. Currently, the collaborative works with LCY Technology Corp. aim to exploit fabricated nanoporous Ni for the hydrogenation of unsaturated organics and thermoplastic elastomers. A collaborative project with Lite-On was built to develop the high reflectance materials in the application of UV LED by exploiting the biomimicking process of butterfly wing structure for photonic metamaterials. From 2013 to 2016, he served as an editorial advisory board member for Macromolecules and ACS Macro Letters. He is also the Associate Editor for Journal of Polymer Research since 2016.