Articles in 2014

An approach to create new artificial materials with hierarchical structures and tailored properties using a layer-by-layer assembly of two-dimensional (2D) oxide nanosheets is demonstrated. 2D nanosheets have remarkable potential as building blocks for tailoring fusion materials combined with a range of foreign materials such as organic molecules, gels, polymers, and inorganic and metal nanoparticles. The ability to create functionalized, 2D hierarchical systems will lead to various applications in optoelectronics, spinelectronics, energy and environment technologies.

An initiating system composed of GaCl₃ and an alkylbenzene was demonstrated to be highly effective for the controlled cationic polymerization of a plant-derived monomer, β-pinene. When two equivalents of hexamethylbenzene were added to GaCl₃ in conjunction with 2-chloro-2,4,4-trimethylpentane as an initiator, cationic polymerization of β-pinene successfully proceeded in a living manner at –78 °C. Successful control over the reaction was attributed to the formation of a complex between GaCl₃ and the alkylbenzene, as confirmed by UV–vis and ⁷¹Ga NMR analyses.

The distribution of polarization during the polarization reversal in a VDF/TrFE copolymer was studied by the piezoresponse force microscopy, PFM. After an application of a positive voltage pulse to a negatively polarized sample, PFM image was obtained. The regions of blue color corresponding to positively polarized domains were shown to nucleate and grow in negatively polarized regions (red color) as the duration of pulse increased. The change of each domain with the pulse duration was analyzed quantitatively and the nucleation rate and the growth speed of domains were obtained separately.

Relationships between the interfacial area between PS and PMMA in a PS/PMMA (1/1, w/w) composite particles including various amounts (white circles 0; filled circles 0.05; white triangles 0.11; filled triangles 0.18 (wt % relative to the total amount of PS and PMMA)) of PS-b-PMMA (B11:Mn 10.6 × 10⁴–b-9.9 × 10⁴) and the required time to cleave into two parts (cleavage time, T_c) by addition of the acetone/water (9:1, v/v) solution to the dried particles

Nanogel particles (NP) that bind with the Fc fragment of immunoglobulin G (IgG) were immobilized on the pore surface of macroporous hard gel beads (GB) containing quaternary ammonium cations on the surface via multipoint electrostatic interactions. The model target protein (IgG) was reversibly captured by the NP-immobilized GBs through NP–IgG interactions. NP-immobilized GBs have potential applications as a novel affinity purification medium for proteins, combining an inexpensive and stable ligand with a high-performance support.

It is widely accepted that native xanthan forms a double helical structure and that it loses this structure upon heating (denaturation) and recovers the double helical structure upon cooling its solution (renaturation). The structure of renatured xanthan depends on the concentration of both xanthan and added salt, and temperature. Branched-rods and hairpin-shaped structures were observed by AFM depending on the conditions of denaturation and renaturation. The structural change observed by atomic force microscopy well agrees with the models proposed in our previous study.

Anti-reflective coating films were fabricated via the layer-by-layer assembly of mesoporous silica nanoparticles and cationic polyelectrolytes. The thickness and packing density of coating films can be controlled by layer number and concentration of mesoporous silica nanoparticle dispersion to obtain excellent anti-reflective performance.

Three-dimensional structural analyses of huge spherulites of poly(oxyethylene) (PEG) using X-ray computerized tomography (CT) in blends of PEG and amorphous poly(d,l-lactic acid) are reported for the first time. Slit-shaped cracks that were straight or curved were clearly observed using X-ray CT. Furthermore, they appeared to form a set of spokes, presenting a signature of a huge spherulite. Several aspects that are representative of an axialite structure are presented, and they are in good agreement with the intuitively proposed structural model for axialite long ago, although the size scale is much larger in our study.

Gold nanoparticles capped with a simplified ionic liquid-like ligand were prepared, which were incorporated into the fusion materials with ionic liquids at concentrations of up to 40 wt% of inorganic content. The fusion material of gold nanoparticles with an ionic liquid monomer was readily converted into a polymeric composite, in which gold nanoparticles showed high thermal stability.

A supramolecular gel of DMSO was formed by pyridyl-substituted tris-urea 1 in the presence of an appropriate amount of Pd(OAc)₂. Scanning electron microscopic image of the xerogel revealed a porous spongiform nanostructure. Gel to sol/solution phase transitions of the supramolecular gel were induced by adding chelating agents to prevent the formation of coordination bonds between 1 and the palladium ion. The Wacker oxidation of styrene was performed in the supramolecular gel, and the reaction kinetics were compared with those in a typical bulk solution.

Gelatin nanofibers were electrospun using mild N,N-dimethylacetamide, N,N-dimethylformamide and N-methyl-2-pyrrolidone. Various gelatin nanofibers were fabricated, ranging from a thick, wide, porous nanofibrous structure to a thin, fine, nanofibrous mesh structure, depending on the solvents and their concentrations. In particular, Swiss 3T3 fibroblasts exhibited in vivo-like spindle morphologies on the thick nanofibers. A model protein, alkaline phosphatase, embedded in the gelatin nanofibers maintained high activity.

Zn-based two-dimensional layer coordination framework was synthesized by ionothermal synthesis and its solid-to-solid phase transition was studied by X-ray diffraction, solid state nuclear magnetic resonance and impedance spectroscopy. The phase transition is originated from the order-to-disorder behavior of accommodated ammonium cations in the structure. It occurs rapidly and reversibly, and little volume change and high thermal stability were observed.

The decoration of a peptide-based artificial viral capsid with gold nanoparticles (AuNPs) is reported. β-Annulus GGGCG-bearing peptide as a binding site of AuNPs self-assembled into nanocapsules with a diameter of 50 nm. The addition of AuNPs to the peptide nanocapsules afforded relatively uncontrolled assemblies of AuNPs. In contrast, the self-assembly of AuNP–peptide conjugates afforded, after dialysis, controlled assemblies of AuNPs with sizes of 30–60 nm. ζ-Potential measurements revealed that the surface of the artificial viral capsid self-assembled from β-annulus peptide was coated with AuNPs.

Sol–gel transition entropy for k-carrageenan/water and gellan/water systems remains constant, regardless of polymer concentration, and species and concentration of added salts.

We investigated the initial photooxidation mechanism leading to reactive radical formation of polythiophene derivatives by focusing on the differences in the photochemical behaviors of photounstable poly(3-hexylthiophene) (P3HT) and photostable poly(3-octyloxythiophene) (P3OOT). Electron spin resonance measurements revealed that the [P3HT]⁺· (formed by oxygen doping) decayed, whereas no change was observed in the photostable [P3OOT]⁺· after light irradiation. Furthermore, the absorption decrease of the [P3HT]⁺· was suppressed by superoxide dismutase. Therefore, the oxygen dopant is superoxide, which might also initiate the oxidation of P3HT.

Poly(methyl methacrylate) surface was fluorinated by simply immersing into 3-(perfluoro-7-methyloctyl)-1,2-epoxypropene, followed by heat treating at 120 °C. The contact angle of water for fluorinated PMMA increased to 111° after the treating. This value corresponds to the surface free energy of 10 mJ m⁻², which is much lower than that (18 mJ m⁻²) of polytetrafluoroethylene. The fluorinated PMMA showed low albumin adsorption. When materials come into contact with blood, protein will rapidly adsorb onto the surfaces, which plays a trigger of clotting. However, protein adsorption was reduced on this very hydrophobic surface.

Fluorescence probe methods were applied to investigate micelle formation of poly(N-isopropylacrylamide) (PNIPA) with surfactant, sodium n-dodecyl sulfate (SDS) or n-dodecyltrimethylammonium chloride (DTAC), in aqueous solutions. Two PNIPA samples, one having a hydrophobic chain-end group (M sample) and the other having a negatively charged hydrophilic chain-end group (R sample), were used to investigate the effects of the chain-end group on the micelle formation. It is found that the microenvironmental polarity in the formed micelles depends on the kinds of chain-end group and surfactant.

In nature, there are many strong and tough biomaterials that result from the fusion of soft and hard elements. These materials include nacre, crustacean exoskeletons and spider webs. Here, we review previous studies on such bio-fusion materials, emphasizing the importance of simple models to gain a physical understanding of the emergence of strength and toughness from these structures. Thus, a simple understanding obtained through biologically inspired models provides useful guiding principles for the development of artificial tough composites by mimicking biomaterials.

Polymeric chain-structured complexes were prepared with helical lanthanide complexes (LnL) and benzene-dicarboxylate derivatives (benzene-1,4-dicarboxylate (bdc), 2-aminoterephtalate (atpa) and 2-hydoloxyterephtalate (htpa)), which show some noteworthy physicochemical properties, photo-luminescence and thermal stabilities. The complex EuL-bdc shows bright luminescence originating from Eu^III by UV excitation. The emission color can be tuned by the mixing of TbL. The structures of these chain complexes were clarified by synchrotron X-ray powder diffraction measurements. The derivation of the linker moiety (bdc to atpa or htpa) affects the inter-metal energy transfer from Tb^III to Eu^III.

Poly(2-(methacryloyloxy)ethyl phosphorylcholine)-block-poly(cholesteryl 6-methacryloyloxyhexanoate) (PMPC₈₂-b-PChM_n) with different PChM block lengths was prepared via controlled/living radical polymerization. To prepare the aqueous solution, the diblock copolymer was dissolved in an organic solvent and then subject to dialyze against pure water. These diblock copolymers formed spherical and rod-like micelles in water depending on the composition of cholesteryl (Chol) group in the polymer. The morphology of the polymer aggregates could be controlled from spherical to rod-like micelles with increasing amount of Chol groups in the polymer.