Application of ER gel with variable friction surface to the clamp system of aerostatic slider

An electro-rheological fluid (ERF) is a functional fluid whose viscoelastic properties vary according to the intensity of the applied electric field. ERFs are mixtures of nonconductive silicone oil and inorganic/organic composite electro-rheological particles. The properties of ERFs have been exploited to control the performance of machine elements. ERFs have been applied to machine elements such as variable dampers and clutches. However, ERFs have disadvantages, namely the sedimentation of ER particles and the requirement of a seal mechanism. The sedimentation of ER particles reduces the ER effects and results in low stability of ER devices. In order to suppress the sedimentation, and thereby improve the performance of ERF devices, a new functional material called the gel-structured ERF (ERG) is developed, whose basic properties are analyzed in this study. The ER particles are suspended in the gel component, and thus will not precipitate out. This suppresses the decrease in the ER effect caused by precipitation. The ERG developed shows a large shear stress variation in response to the applied electric field. This high performance of ERG originates in a mechanism different from the ER effects of ERF. In order to elucidate the mechanism in ERG, the behavior of ER particles was observed under an electric field. The results show that the contact conditions at the interface between electrode and ERG change rapidly in response to the applied electric field, which result in a variation in shear force. On the basis of the results of a preliminary analysis, ERG was applied to the precision clamp system of an aerostatic slider, and its performance was assessed experimentally.     

Surface properties of polymer films including multiblock copolymer

B(AB)_n multiblock copolymers of which the A block and the B block are hydrophobic and hydrophilic, respectively, were blended into crosslinkable coating compositions for preparing a hydrophilic surface, and compared with the graft copolymers including A and B as the pendant groups. The main constituent of A was polydimethyl-siloxane and that of B was poly(ethylene oxide). While the block copolymer slightly increased the hydrophobicity of the surface, it quickly became hydrophilic on contact with water. On the contrary, the graft copolymer increased the hydrophobicity even after its contact with water. Elementary analysis with ESCA demonstrated that both the silicon atoms and ether groups were concentrated on the very top of the surface in the films including the block copolymers but only silicon atoms were concentrated on the film surface which included the graft copolymers. In spite of their propensity to remain in the bulk due to their high surface energy, hydrophilic poly(ethylene oxide) moieties in the block copolymers migrated onto the near surface accompanying the movement of the hydrophobic polydimethyl-siloxane. because their mobility would be restricted by the bonding of both sides. Inclusion of the block copolymers significantly improved soil resistance. The advantage of the block copolymers as a surface modifier was further developed as an adhesion promoter. The introduction of a larger amount of the hydroxyl group into the hydrophilic block was effective for this purpose. This was discussed with respect to the change in the γ_p parameter.     

Thermoresponsive PEG‐Coated Nanotubes as Chiral Selectors of Amino Acids and Peptides

A series of nanotubes with a dense layer of short poly(ethylene glycol) (PEG) chains on the inner surface are prepared by means of a coassembly process using glycolipids and PEG derivatives. Dehydration of the PEG chains by heating increases the hydrophobicity of the nanotube channel and fluorescent‐dye‐labeled amino acids are extracted from bulk solution. Rehydration of the PEG chains by cooling results in back‐extraction of the amino acids into the bulk solution. Because of the supramolecular chirality of the nanotubes, amino acid enantiomers can be separated in the back‐extraction procedure, which is detectable with the naked eye as a change in fluorescence as the amino acids are released from the nanotubes. The efficiency and selectivity of the chiral separation are enhanced by tuning the chemical features and inner diameter of the nanotube channels. For example, compared with wide nanotube channels (8 nm), narrow nanotube channels (4 nm) provide more effective electrostatic attraction and hydrogen bond interaction environments for the transporting amino acids. Introduction of branched alkyl chains to the inner surface of the nanotubes enables chiral separation of peptides containing hydrophobic amino acids. The system described here provides a simple, quick, and on‐site chiral separation in biological and medical fields.     

Anti-allergic effect of strawberry extract

We examined the anti-allergic effect of strawberry extract on human peripheral blood mononuclear cells (PBMCs) and atopic dermatitis model mice NC/NgaTndCrlj. The addition of strawberry extract suppressed total IgE production in the cedar pollen antigen Cry j 1-stimulated PBMCs. Flow cytometric analysis showed that strawberry extract decreased the rate of CD3⁺CD4⁺ helper T cells by 17.3% and increased the rate of CD3⁺CD8⁺ cytotoxic T cells by 19.7% in PBMCs. Moreover, the extract inhibited the expression level of GATA3 that is the master regulator of type 2 helper T cells (Th2) in human primary pan T cells isolated from PBMCs. Oral administration of strawberry extract lowered dermatitis scores and serum IgE levels in mice. In addition, it also decreased the GATA3 expression level in mouse blood cells. These results revealed that strawberry extract suppressed the severity of atopic dermatitis through the down-regulation of serum IgE by inhibition of Th2 differentiation.     

Design of a rigid side chain for poly(N-vinylamide) derivatives bearing an alkenyl group and evaluation of their ability to inhibit tetrahydrofuran hydrate crystal growth

Kinetic hydrate inhibitors (KHIs) are water-soluble polymers that are used to prevent gas hydrate formation in flow lines during upstream oil and gas production. All commercial polymers have pendant hydrophobic moieties with saturated carbon–carbon bonds. In our previous studies, poly(N-vinylamide) derivatives bearing alkyl groups and ethylene glycol groups were synthesized and investigated as KHIs. For comparison, we have now synthesized poly(N-vinylamide) derivatives in which an alkenyl group has been introduced at the N-position to improve the rigidity and steric hindrance of the side chain. The KHI performances of synthesized polymers were evaluated by the method of tetrahydrofuran (THF) hydrate crystal growth. The molecular weight of the synthesized polymers affected their ability to inhibit THF hydrate crystal growth. Higher molecular weight polymers, above 4,000 g/mol, tended to show higher inhibition efficiencies compared with lower molecular weight polymers of around 1,000 g/mol. However, the KHI performance of poly(N-vinylamide) derivatives bearing alkenyl groups was generally lower than the polymers in the previous studies. This indicates that the side chain rigidity and/or steric hindrance do not significantly influence the KHI performance.     

Surface control of hydrophilicity and degradability with block copolymers composed of lactide and cyclic carbonate bearing methoxyethoxyl groups

Block copolymers of L-lactide (LA) and trimethylene carbonate (TMC) derivatives bearing methoxyethyl groups [poly(TMCM-MOE1OM)-block-PLLA] were employed as spin-coated films on substrates, and their hydrophilic and degradation behaviors were investigated. Changing the solvents for film preparation, film thickness, and copolymer composition ratios varied the contact angles in the range of 84.3° ± 2.8° at 269 nm thickness and 18.2° ± 2.5° at 15 nm thickness. These contact angles showed dynamic changes from hydrophobic to hydrophilic properties, probably due to the methoxyethoxyl groups connecting the flexible TMC moieties in the copolymer. Immersion into water or hexane affected the dynamic contact angles. X-ray photoelectron spectroscopy analyses revealed that a large amount of hydrophilic groups was segregated onto the surface, although both LA and TMC units existed. Such dynamic contact angle changes were delayed by the crystallization of polylactide. The hydrolyzed behaviors of these films were examined by quartz cell microbalance, showing a slow degradation process.     

Effect of copolymerizing fluorine‐bearing monomers on the relationship among internal structure,gas permeability,and transparency in copolymer networks composed of methacrylates and siloxane macromers

To clarify the effect of the type of acrylic monomer and the molecular weight (M_n) of polydimethylsiloxane (PDMS) on the relationship among the internal structure, oxygen permeability coefficient [P(O₂)] and transparency, crosslinked copolymers were prepared with two different acrylic monomers : methyl methacrylate (MMA) and trifluoroethyl methacrylate (TFEMA). PDMS macromers with M_n of 1700, 3300, 4700, and 7800 g/mol were used. DSC measurements suggested that all constituent phases were insoluble with each other. The M_n of PDMS affected both the light transmittance and P(O₂). The relationship between the M_n and P(O₂) over the low M_n range (1700 and 3300 g/mol), and the calculated PDMS domain size ratio, were found to support the [M_n]^2/3 rule into the crosslinked copolymer. Furthermore, a 3300 g/mol M_n copolymer became transparent when the amount of PDMS was greater than PMMA. In addition, copolymerization with TFEMA drastically affected those properties, and this effect was much greater than the effect of the PDMS M_n. To clarify the mechanism of P(O₂) improvement induced by TFEMA copolymerization, calculations on the relationship among the P(O₂), PDMS volume fraction, and morphology model were performed, and some properties such as solubility parameters should play important roles. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Transmission electron microscopic observations of the multilevel microstructure of crosslinked copolymers with methacrylates and siloxane macromers by a radically polymerizable tuning approach

We investigated by Transmission Electron Microscopy (TEM) the morphologies of crosslinked copolymers from methacrylate monomers from methylmethacrylate (MMA) and trifluoroethylmethacrylate (TFEMA), polydimethylsiloxane (PDMS) macromers with molecular weight (Mn) of 1,700 and 4,700 g/mol, and crosslinker. Depending on the PDMS content, we observed, spherical PMMA islands in which small PDMS domains were dispersed, PMMA continuous phase, closely packed PTFEMA islands, and homogeneously dispersed PDMS domains were observed with low or middle magnification. Fine observation at 100,000‐fold magnification revealed the “fundamental” common size domain, which was determined by the M_n value of the PDMS macromer. Thus we found two microstructure types: (1) a “fundamental domain” due to the M_n of the PDMS macromer, and (2) an aggregated domain. The former was constant under all conditions, but the latter was affected by the comonomer and its ratio. The present results are essential in understanding the chemical and physical characteristics of crosslinked copolymers from PDMS macromers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Layer-by-layer assembly through weak interactions and their biomedical applications

The surface design and control of substrates with nanometer- or micrometer-sized polymer films are of considerable interest for both fundamental and applied studies in the biomedical field because of the required surface properties. The layer-by-layer (LbL) technique was discovered in 1991 by Decher and co-workers for the fabrication of polymer multilayers constructed mainly through electrostatic interaction. The scope and applicability of this LbL assembly has been extended by introducing molecularly regular conformations of polymers or proteins by employing, for the first time, weak interactions such as van der Waals interactions and biological recognition. Since these weak interactions are the sum of the attractive or repulsive forces between parts of the same molecule, they allow macromolecules to be easily arranged into the most stable conformation in a LbL film. By applying this characteristic feature, the template polymerization of stereoregular polymers, stereoregular control of surface biological properties, drastic morphological control of biodegradable nano materials, and the development of three-dimensional cellular multilayers as a tissue model were successfully achieved. It is expected that LbL assembly using weak interactions will promote further interest into fundamental and applied studies on the design of surface chemistry in the biomedical field.     

Observation of internal pulsed current flow through the ZnO specimen in the spark plasma sintering method

In spark plasma sintering (SPS), it is supposed that a part of the large pulsed sintering current flows into the specimen and affects the sintering behavior. To clarify the influence of the internal pulsed current that flows through the specimen during SPS, measurement of the electrical resistance of the specimen was conducted using Pt electrodes and the internal pulsed current was successfully observed using a magnetic probe during the sintering of ZnO and other materials. Two Pt electrodes were installed on the sides of a ZnO sample through a carbon die, and decrease of electrical resistance was observed with the progress of sintering. The internal current that flows through the specimen during SPS was several hundred ampere, and the ratio of the internal current to the total current was found to be dependent on the material and the progress of SPS process.