Shiao-Wei Kuo

Hierarchical self-assembly and secondary structures of linear polypeptides graft onto POSS in the side chain through click chemistry

In this study, we used click chemistry to synthesize a new macromolecular self-assembling building block, linear polypeptide-g-polyhedral oligomeric silsesquioxane (POSS) copolymers, from a mono-azido-functionalized POSS (N3-POSS) and several poly(γ-propargyl-L-glutamate) (PPLG) oligomers. The incorporation of the POSS unit on the side chain of the PPLG moiety enhanced the α-helical conformation in the solid state, as determined by Fourier transform infrared spectroscopy, solid state nuclear magnetic resonance and wide-angle X-ray diffraction analysis. PPLG-g-POSS underwent hierarchical self-assembly, which was characterized using small-angle X-ray scattering and wide-angle X-ray diffraction analyses, to form a hexagonal cylinder packing nanostructure featuring α-helical conformations and POSS aggregates. The attachment of POSS onto the side chain of PPLG could stabilize the α-helical secondary structure with an increase in temperature, compared with pure PPLG by temperature-dependent FTIR analyses.

Hierarchical self-assembly structures of POSS-containing polypeptide block copolymers synthesized using a combination of ATRP, ROP and click chemistry

In this study, we used a combination of atom transfer radical polymerization, ring opening polymerization, and click chemistry to synthesize new organic/inorganic macromolecular self-assembling building blocks of polystyrene-b-poly(γ-propargyl-L-glutamate-g-polyhedral oligomeric silsesquioxane) [PS-b-(PPLG-g-POSS)]. The incorporation of the PS and POSS units enhanced the α-helical conformation in the solid state, as determined using Fourier transform infrared (FTIR) spectroscopy and wide-angle X-ray diffraction (WAXD). Hierarchical self-assembly of the PS-b-(PPLG-g-POSS) diblock copolymers, which we characterized using WAXD, small-angle X-ray scattering, and transmission electron microscopy, led to the formation of cylindrical structures as a result of microphase separation of the diblock copolymer; the hexagonal cylinder packing nanostructure featured α-helical conformations of polypeptide segments, which were oriented perpendicular to the direction of the cylinder column from diblock copolymers; aggregation of the POSS moieties induced the packing into hexagonal lattice structures. The attachment of POSS units onto the side chains of PPLG stabilized the α-helical secondary structures at elevated temperature, relative to those of pure PPLG and PS-b-PPLG, as determined through temperature-dependent FTIR spectroscopic analyses.

Heteronucleobase-functionalized benzoxazine: synthesis, thermal properties, and self-assembled structure formed through multiple hydrogen bonding interactions

In this study we prepared a new class of thymine (T)-functionalized polybenzoxazine (PBZ) through the Michael addition of T to a new acryloyl-functionalized [(3-phenyl-3,4-dihydro-2H-benzooxazin-6-yl)methyl acrylate]benzoxazine (PA-ac) monomer and subsequent polymerization. We used 1H and 13C nuclear magnetic resonance spectroscopy and Fourier transform infrared (FTIR) spectroscopy to confirm the chemical structure of this new monomer and then employed differential scanning calorimetry (DSC) and FTIR spectroscopy to study the curing behavior of the new PBZ. The presence of the strongly self-complementary, multiply hydrogen-bonded T units in the PBZ matrix significantly enhanced its thermal stability, as evidenced from DSC traces and thermogravimetric analyses. Transition electron microscopy and wide-angle X-ray diffraction data provided evidence for the self-assembly of the PBZ occurring through self-complementary multiple hydrogen bonding of its T units.

Complexing AIEE-active tetraphenylthiophene fluorophore to poly(N-isopropyl acrylamide): fluorescence responses toward acid, base and metal ions

In this article, a multiple-responsive polymer micelles system was constructed by using an ionic bond as the link to connect the hydrophobic tetraphenylthiophene (TP) fluorophores having aggregation-induced emission enhancement (AIEE), and the hydrophilic poly(N-isopropyl acrylamide) (PNIPAM). The susceptibility of the ionic ammonium-sulfonate (Am-Sul) bond towards metal ions, acid and base triggered the AIEE-operative fluorescence (FL) response. To exercise the idea, PNIPAM with a sulfonate terminal was primarily prepared to react with an ammonium-functionalized TP derivative to generate a polymer complex of TP-PNIPAM. When in water, the polymer complex TP-PNIPAM formed micelles with the aggregated TP core interconnecting the hydrophilic PNIPAM shell by the ionic Am-Sul bonds. With the operative AIEE effect, the aggregated TP core in the micelles fluoresced strongly but upon the additions of metal ions, acid and base, the ionic bonds dissociated to result in the collapse of the micelles and the corresponding emission quenching. A novel fluorogenic sensor capable of responding to multi-stimuli was therefore constructed.

Liquid Lenses and Driving Mechanisms: A Review

Abstract In this paper, we discuss liquid lenses driven by various mechanisms. By properly designing the device structure and choosing the optimal materials, the liquid lenses offer great potential for practical uses. The driving mechanism dictates the application and performance of the liquid lenses. Here we categorize the driving mechanisms into mechanical and electrical ones. In general, mechanical driving with an elastic membrane and an external pump drives liquids in a cavity by controlling the hydraulic pressure. The mechanical driving method can be applied to most of the liquids, but the application of the electrical driving method would be limited by the conductivity or the permittivity of the liquids. Therefore, the properties of the different liquids, e.g., dielectric liquids, liquid crystal molecules, and conductive liquids, deeply affect the mechanism we may choose to realize a liquid lens. Among various electrical methods, dielectrophoresis (DEP), electrostatic forces, and electrowetting-on-dielectric (EWOD) are emphasized here for driving dielectric liquids, liquid crystal molecules, and conductive liquids, respectively. DEP deforms the liquid lenses when the permittivities are different between the liquid and the medium. Electrostatic force orients the liquid crystal molecules to follow the applied electric field. Electrowetting-driven liquid lenses change their focal lengths by altering the contact angle. Here we show the designs and the structures of liquid lenses to describe their mechanisms, performances and feasibilities. It is worth mentioning that the liquid lenses using electrowetting have been commercialized. No moving parts would be the most important reason to use electrical manipulations rather than mechanical ones.

Complementary multiple hydrogen bonding interactions mediate the self-assembly of supramolecular structures from thymine-containing block copolymers and hexadecyladenine

In this study we used nitroxide-mediated radical polymerization to synthesize poly(styrene-b-4-vinylbenzyl azide) (PS-b-PVBN3) and then used click chemistry to react it with propargyl-thymine (PT) to obtain a series of thymine (T)-containing block copolymers, poly(styrene-b-4-vinylbenzyl triazolylmethyl methylthymine) (PS-b-PVBT). We then added an amphiphilic surfactant, hexadecyladenine (A-C16), to complex with the PVBT units in the PS-b-PVBT copolymers through complementary multiple hydrogen bonding interactions. The resulting supramolecular comb–coil diblock copolymers formed lamellae-within-lamellae self-assembled structures, with PS lamellar domains (diameter: ca. 20–25 nm) in a matrix consisting of lamellar mesophases (lamellar inter-distance: ca. 2.3 nm) organized by the PVBT/A-C16 complex. Fourier transform infrared spectroscopy provided evidence for multiple hydrogen bonding between the A-C16 and T groups of the PS-b-PVBT copolymers. The small-angle X-ray scattering patterns of these self-assembled supramolecular systems were very temperature-sensitive. A striking feature was the appearance of the ordered scattering of the lamellar structure at temperatures higher than the melting point of A-C16 (>120 °C), with A-C16 becoming fully miscible with both the PS and PVBT phases at higher temperature; A-C16 was miscible only with the PVBT domains at room temperature, thereby influencing the volume fraction of the PS segment.

Aggregation induced emission enhancement in relation to the secondary structures of poly(γ-benzyl-L-glutamate) containing a fluorescent tetraphenylthiophene moiety

In this study, tetraphenylthiophene (TP) with aggregation-induced emission enhancement (AIEE) property served as the terminal and central fluorophores of poly(γ-benzyl-L-glutamate) (PBLG)-based polymers of TP1PBLG and TP2PBLG, respectively, to probe the relationship between the secondary structure (α-helix) of polypeptides and the AIEE-operative fluorescence (FL). Intermolecular aggregation of the central TP unit in the di-substituted TP2PBLG is sterically blocked by the large α-helical PBLG chains, which leads to the reduced AIEE-oriented FL. In contrast, the terminal TP units in TP1PBLG can easily approach each other to form aggregates with strong FL. Factors (e.g. solvent annealing) controlling the fraction of the α-helix chain also vary the corresponding emission intensity. The conformational difference between TP1PBLG and TP2PBLG evaluated from the infrared and the X-ray (wide- and small-angle) diffraction spectra is also used to verify its influence on the AIEE-operative FL behavior.

Using colloid lithography to fabricate silicon nanopillar arrays on silicon substrates

In this study, we partially grafted geminal silanol groups in the protecting organic shells on the surfaces of gold nanoparticles (AuNPs) and then assembled the alkyl-AuNP-Si(OH)(4) particles onto the surfaces of silicon (Si) wafers. The density of assembled AuNPs on the Si surface was adjusted by varying the geminal silanol group content on the AuNP surface; at its optimal content, it approached the high assembly density (0.0254 particles/nm(2)) of an AuNP assembled monolayer. Using reactive-ion etching (RIE) with the templates as masks, we transferred the patterned AuNP assemblies to form large-area, size-tunable, Si nanopillar arrays, the assembly density of which was controlled by the dimensions of the AuNPs. Using this colloidal lithography (CL) process, we could generate Si nanopillars having sub-10-nm diameters and high aspect ratios. The water contact angles of the high-aspect-ratio Si nanopillars approached 150°. We used another fabrication process, involving electron beam lithography and oxygen plasma treatment, to generate hydrophilic 200-nm-resolution line patterns on a Si surface to assemble the AuNPs into 200-nm-resolution dense lines for use as an etching mask. Subsequent CL provided a patterned Si nanopillar array having a feature size of 200 nm on the Si surface. Using this approach, it was possible to pattern sub-10-nm Si nanopillar arrays having densities as high as 0.0232 nm(-2).

Supramolecular ionic strength-modulating microstructures and properties of nacre-like biomimetic nanocomposites containing high loading clay

In this study, we prepare thick nacre-like polymer clay nanocomposite films by a simple solution casting method. Nanoclay sheets with soft polymer coatings are used as ideal building blocks with intrinsic hard/soft character. The water-soluble poly(vinyl alcohol) (PVA) was chosen as an organic binder to connect each smectic clay sheet in the form of a nacre-like microstructure. The polymer-clay composite is in the form of a membrane in which the clay sheets are like stacked bricks. In addition, when applying normal stress larger than the yield stress—about 40 MPa—white shear bands develop at strains larger than 10%, much like the conditions where crazing of organic PVA is suppressed by inorganic fillers of clay sheets. Their corresponding microstructure and mechanical properties are studied using wide angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques and a tensile testing machine and are discussed in detail.

Using a polyhedral oligomeric silsesquioxane surfactant and click chemistry to exfoliate montmorillonite

In this study, we prepared exfoliated montmorillonite (MMT) through Huisgen [2 + 3] cycloadditions (click reactions) of a propargyl-containing intercalator with singly or multiply azido-functionalized polyhedral oligomeric silsesquioxane nanoparticles. Wide-angle X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, and thermogravimetric analyses revealed the structures and properties of the products, which have the potential to be used directly through simple polymer blending or copolymerization to improve the physical properties of polymer-based clay nanocomposites.