Jae Young Jho

A new fabrication method for IPMC actuators and application to artificial fingers

IPMC (ionic polymer metal composite), a kind of ionic electroactive polymer (EAP), has been used for various applications because it has light weight and can make large bending deformation under low driving voltage. In the present work, thick IPMC films were fabricated by hot-pressing several thin IPMC films and the actuating performance was evaluated. Displacement and maximum load with applied voltage were measured using a displacement measuring system, a load cell and a multimeter. Several cycles of Pt electroless-plating were performed on the IPMC films to improve the actuating performance. Then, SEM (scanning electron microscopy) micrographs and EDS (energy dispersive spectrometer) profiles of the IPMC specimen were examined. To demonstrate the feasibility of IPMC films for medical or robotic applications, the developed IPMC actuators were applied to artificial fingers and tested.

Preparation of clay-dispersed poly(styrene-co-acrylonitrile) nanocomposites using poly(ϵ-caprolactone) as a compatibilizer

Abstract Poly(styrene-co-acrylonitrile) (SAN)/organoclay nanocomposites were prepared using poly(ϵ-caprolactone) (PCL) as a compatibilizer. Two-step mixing sequence was used to prepare the SAN nanocomposites: PCL/organoclay master batches with different degree of intercalation were prepared by melt mixing first, and then they were melt-mixed with SAN, where PCL is miscible with SAN. The intercalation behavior of PCL in the master batches was investigated in terms of the type of organic modifier and mixing conditions such as shear rate, mixing temperature and mixing time. Longer mixing time and lower mixing temperature were required to prepare exfoliated PCL master batches. As the degree of exfoliation of clays becomes better, the stiffness reinforcement effect of the organoclays increases in both PCL/organoclay master batches and their blends with SAN.

Self-assembled discotic nematic liquid crystals formed by simple hydrogen bonding between phenol and pyridine moieties

New discotic nematic liquid crystals have been prepared through intermolecular hydrogen bonding between the core of 1,3,5-trihydroxybenzene (phloroglucinol, PG) or 1,3,5-tris(4-hydroxyphenyl)benzene (THPB) and the peripheral molecules of stilbazole derivatives. The various nematic phases formed by new hydrogen bonding building blocks were investigated by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. The first discotic complexes of PG and trans-4-alkoxy-4′-stilbazoles exhibited nematic columnar (NC) and hexagonal columnar phases depending on the length of alkyl chains, which were considered as the basic discotic structure. Several structural variations on the building blocks were attempted to examine their effects on the liquid crystalline properties of discotic complexes. The nematic lateral phase (NL) with enhanced intercolumnar order was observed for the complexes of PG and trans-4-cyanoalkoxy-4′ stilbazoles due probably to the strong dipole interactions between cyano groups at the end of alkoxy chains. By introducing the nonlinear structure in three arms of supramolecular discotic mesogen, a discotic nematic phase (ND) was observed for the complex of THPB and trans-4-octyloxy-4 -stilbazole. The single hydrogen bonding between phenol and pyridine moieties in this study provides a simple and effective method for preparing the rarely found discotic nematic liquid crystals.

Effect of molecular weight between crosslinks on the fracture behavior of rubber-toughened epoxy adhesives

The effect of molecular weight between crosslinks, Mc, on the fracture behavior of rubber-toughened epoxy adhesives was investigated and compared with the behavior of the bulk resins. In the liquid rubber-toughened bulk system, fracture energy increased with increasing Mc. However, in the liquid rubber-toughened adhesive system, with increasing Mc, the locus of joint fracture had a transition from cohesive failure, break in the bond layer, to interfacial failure, rupture of the bond layer from the surface of the substrate. Specimens fractured by cohesive failure exhibited larger fracture energies than those by interfacial failure. The occurrence of transition from cohesive to interfacial failure seemed to be caused by the increase in the ductility of matrix, the mismatch of elastic constant, and the agglomeration of rubber particles at the metal/epoxy interface. When core-shell rubber, which did not agglomerate at the interface, was used as a toughening agent, fracture energy increased with Mc.

Star-shaped supramolecular liquid crystals formed by hydrogen bonding between phloroglucinol and stilbazole derivatives with different molecular shapes

Three types of the stilbazole derivative, 4-(4-alkoxybenzoyloxy)-4′-stilbazole (nSz), 4-(3,4-dialkoxybenzoyloxy)-4′-stilbazole (nDSz), and 4-(3,4,5-trialkoxybenzoyloxy)-4′-stilbazole (nTSz), were synthesised and complexed via hydrogen bonding with phloroglucinol (PG) to build liquid crystals, and their mesomorphic properties were investigated. In PG/nSz complexes, a wider mesomorphic range was observed than in nSz. The types of observed mesophases were nematic (n = 6, 8) and smectic phases (n = 10, 12). PG/nDSz and PG/nTSz complexes showed mesophases which were not observed for the non-complexed components. Monotropic nematic phases were observed for the PG/nDSz complexes, and PG/nTSz complexes exhibited hexagonal columnar structures. Based on the X-ray diffraction data, schematic models for the molecular arrangement were proposed for the smectic, nematic and hexagonal columnar phases of the complexes.

Mechanical properties of ultra-high molecular weight polyethylene irradiated with gamma rays

With the goal of enhancing the creep resistance of ultra-high molecular weight polyethylene (UHMWPE), we performed gamma irradiation and post-irradiation annealing at a low temperature, and investigated the crystalline structures and mechanical properties of the samples. Electron spin resonance spectra reveal that most of the residual radicals are stabilized by annealing at 100 °C for 72 h under vacuum. Both the melting temperature and crystallinity increase after increasing the dose and by post-irradiation annealing. When irradiated with the same dose, the quenched sample having a higher amorphous fraction exhibits a lower swell ratio than does the slow-cooled sample. The measured tensile properties correlate well to the crystalline structure of the irradiated and annealed samples. For enhancing creep resistance, high crystallinity appears to be more critical than a high degree of crosslinking.

Gas transport and dynamic mechanical behavior in modified polysulfones with trimethylsilyl groups: effect of degree of substitution

Trimethylsilyl (TMS) groups were introduced with controlled degree of substitution (DS) onto the phenylene rings of various polysulfones. The introduction of TMS groups resulted in a marked increase in oxygen permeabilities with small concurrent decreases in oxygen/nitrogen permselectivities. Although TMS groups are bulky, they are highly mobile and are expected to reduce chain packing as evidenced by larger specific volumes and d-spacings with increasing DS. The higher is DS, the greater the reduction in the chain packing that occurs. Dynamic mechanical analyses of sub-glass-transition relaxation, i.e., γ-relaxation behavior, showed that the TMS groups affected the local chain motion. In particular, the motion of unsubstituted phenylene rings increases with DS. Therefore, both the loosened chain packing and the increased local motion by substitution of TMS may result in the increase in the gas permeability.

Miscibility of poly(ethylene terephthalate)/poly(estercarbonate) blend

Abstract The miscibility of poly(ethylene terephthalate) (PET) with polyarylate (PAr), polycarbonate (PC), and poly(estercarbonate) (PEC), polyarylate–polycarbonate random copolymer were examined from thermal properties, and morphology. PAr, PC and PEC all showed phase separation behavior in blends with PET. On the other hand, as the carbonate/ester repeating unit ratio increases, the penetration of PEC into PET tends to increase, and the corresponding suppression of crystallization was observed. In SEM study, on the contrary, the apparent morphology was resulted in as if PET and PEC1 are more favorable, which is attributed to the fact that in morphology the control processing condition can be a dominant factor for immiscible blend systems

Modified polysulfones 5: synthesis and characterization of tetramethyl polysulfones containing trimethylsilyl groups and their gas transport properties

Polysulfones with rigid backbone structures and silyl-containing substituents were prepared as membrane materials with potentially enhanced gas transport properties. Tetramethylbisphenol-A polysulfone (TMPSf) and tetramethylbiphenol polysulfone (TMPPSf) were made by polycondensation then post-modified to introduce trimethylsilyl (TMS) groups by bromination and lithiation methodology. Substitution of high levels of TMS groups at the ortho-sulfone sites was achieved using direct lithiation followed by addition of a trimethylsilane electrophile. In an approach to increase the overall TMS substitution level as well as introduce these groups on the bisphenol segment, both TMPSf and TMPPSf were cleanly brominated to a degree of substitution (DS) of 2.0 for bromine. While the subsequent lithium–halogen exchange and reaction with TMS electrophile did not give high regioselectivity because of steric hindrance, the overall DS of TMS in the polymers was increased when excess n-butyllithium was used to activate both brominated and ortho-sulfone sites. The polymer structures were characterized by NMR spectroscopy. Their thermal properties as well as O2, N2, CO2 and CH4 gas transport properties were measured. Polymers with a high DS of TMS had very high CO2 and O2 permeabilities and good permselectivities from N2. The permselectivities of CO2/N2 were at or close to the Robeson upper-bound performance line [J. Membr. Sci. 62 (1991) 165].

The effect of dope solution characteristics on the membrane morphology and gas transport properties : PES/γ-BL/NMP system

The effect of heterogeneity of a dope polymer solution on membrane morphology has been investigated. Heterogeneity was developed in polyethersulfone solutions of either γ-butyrolactone (γ-BL) or a mixed solvent of γ-BL/N-methyl-2-pyrrolidone, which exhibit gelation and/or phase separation with aging time. Two different processes for membrane preparation have been employed; Process I, heterogeneity-developed dope solution was cast on a glass plate with a knife for uniform thickness, and immediately immersed into a nonsolvent form of the membrane. Process II, a dope solution was cast on a glass plate and then aged in a closed environment. After a certain aging time, it was immersed into a nonsolvent to be coagulated. The developed heterogeneity was destroyed markedly during casting in Process I, whereas the heterogeneity was maintained until the moment of immersion into a coagulation medium in Process II. Membranes prepared by Process I were finger-like regardless of the aging time, whereas Process II yielded macrovoid-free and sponge-like membranes having enhanced gas permeance and mechanical strength at long aging times. From these results, it was concluded that the morphology and transport properties of a membrane were able to be controlled by the solution structure, in particular, the solution heterogeneity in the cast film.