摘要:

AbstractDragline silk from the spider,Nephila clavipes, was characterized by thermal analysis (TGA, DSC, DMA), computational modeling, scanning electron microscopy and by quasi‐static as well as high rates of strain. Thermal stability to about 230°C was observed by TGA, two transitions by DMA, −75°C, representative of localized motion in the amorphous domain, and a main chain motion associated with partial melt at 210°C. Tensile tests indicated average initial modulus, ultimate tensile strength and ultimate tensile strain of 22 GPa, 1.1 GPa and 9%, respectively. The corresponding properties of the best fibers tested were 60 GPa, 2.9 GPa and 11%, respectively. High strain rates (>50,000%/sec) indicated similar mechanical properties to the average values indicated above. Microscopy showed compressive and tensile strains to failure of 34%. Computational modeling yielded a crystal modulus of 2

ISSN:1042-7147    

DOI:10.1002/pat.1994.220050801

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractHorse‐heart myoglobin (Mb) was modified with poly(ethylene oxide) (PEO) to solubilize it in PEO oligomers. PEO‐modified Mb (PEO–Mb) showed a quasi‐reversible electrochemical redox reaction in PEO200(molar mass of 200 g). PEO–Mbs, modified with lower molecular weight of PEO chains, were soluble in PEO oligomers with wider range of molecular weight. A conformation of PEO–Mb was studied with circular dichroism spectroscopy in phosphate buffer solution (PBS) or PEO oligomers. The α‐helix content of PEO–Mb, determined by the molar ellipticity at 222 nm, decreased from 71% to about 58% after PEO modification. However, the degree of PEO modification did not affect the α‐helix content of PEO–Mbs. On the other hand, the α‐helix content of PEO–Mbs was reduced by lowering the molecular weight of the modified PEO chains. Since the α‐helix content of PEO–Mb in PBS and that in the PEO oligomers were almost identical, the conformation of PEO–Mb in PBS was considered to be maintained even in PEO oligomers. Although the reduction rate constant of PEO–Mb in PEO oligomers depended on the total molecular weight of the PEO–Mbs, their relation did not obey the Stokes–Einstein equation. The reduction of the PEO–Mb was probably affected by the interfacial electron transfer process at the electrode surface rat

ISSN:1042-7147    

DOI:10.1002/pat.1994.220050802

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractRecently, flexible rod‐like monomers based on conformational isomerism have been used to synthesize fully aromatic thermotropic polymers of reduced processing temperature and good thermal stability. 3,4′‐Dihydroxy and 3,4′‐dicarboxydiphenyl ethers HE and DE, obtained by modified Ullmann condensations between proper hydroxy and bromo derivatives, are investigated as basic components for homo‐ and copolyesters with the above‐mentioned characteristics. Homopolymers from HE and terephthaloyl chloride or DE chloride and 2‐methyl (or phenyl) hydroquinone, synthesized by low temperature solution polycondensation, melt to an isotropic fluid; the chain packing is frustrated in the latter by asymmetrical substitution on the aromatic rings, which causes a sequence randomization as well as an increased chain separation. The incorporation of linear rigid units, by partial substitution of the flexible monomers with 1,4 aromatic moieties, leads to thermotropicity, but the critical content of 1,4 units varies with the steric hindrance of the diphenol. Variation of chain rigidity, arising from the chemical structure, composition and sequence distribution, can account for the thermal behavior of the samples and, in particular, for their different abilities to give liquid cryst

ISSN:1042-7147    

DOI:10.1002/pat.1994.220050803

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractBlends of polyarylate of bisphenol A, PAr, with two commercial main chain liquid crystalline polymers, Vectra A950 and Vectra B950, are studied. From dynamic viscoelastic measurements it is deduced that both systems (PAr/Vectra A950 and PAr/Vectra B950) are immiscible and scanning electron microscopy (SEM) micrographs show the presence of spherical domains of the liquid crystalline polymer when PAr constitutes the matrix. Extrusion capillary measurements reveal that, under conditions of temperature and shear rate similar to those of processing, the viscosity is reduced to approximately 10% of its value when the content of liquid crystalline polymer is only 20%. This great improvement of the rheological properties is observed in both PAr/Vectra A950 and PAr/Vectra B950 blends. The effect of draw ratio on Young's modulus for different compositions is also analyzed, pointing out the reinforcing action of both liquid crystalline polymers on polyarylate: for instance, 20% of Vectra B950 in the blend gives rise to a 700% increase of the modulus of fibres prepared at a draw ratio of 50. SEM of the extrudates reveals that the spherical domains are elongated at the entrance of the capillary giving rise to a microfibrillar morphology which is related to the excellent rheological and mechanical properties of the blends.

ISSN:1042-7147    

DOI:10.1002/pat.1994.220050804

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe characteristics of the copper deposition process from electrochemical cells using a solution of Cu(CF3SO3)2in low molecular weight poly(ethylene glycol), PEG, have been investigated by cyclic voltammetry, potential steps and impedance spectroscopy. The results suggest that under non‐equilibrium at the cathodic side the process mainly involves the reduction of Cu(II) ions to copper metal while at the anodic side a chemical reaction competes with the electrochemical dissolutio

ISSN:1042-7147    

DOI:10.1002/pat.1994.220050805

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractWe investigated cholesteric liquid crystals containing an anisotropic polymer network created by in situ photo‐polymerization of a mesogenic diacrylate. In contrast to previous studies, we used a liquid crystalline diacrylate to achieve bistable switching between the reflecting Grandjean texture and the diffuse scattering focal conic texture. The switching behavior depends considerably on the orientation of the liquid crystal during the polymerization. For polymerization in the Grandjean texture, the response times for switching to the reflecting state were lowered compared to the pure liquid crystal. The chromaticity coordinates indicate that this new type of display is very promising for additive color mixin

ISSN:1042-7147    

DOI:10.1002/pat.1994.220050806

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractA series of PMDA‐, BTDA‐ and 6F‐polyamideimides containing well‐defined oligo(tetrafluoroethene) segments were derived from N,N′‐bis(aminophenyl)perfluoroalkane‐α, ω‐dicarboxamides with n =1,2,3 tetrafluoroethene units. The influence of the fluorine content, microstructures and the oligo(tetrafluoroethene) segment lengths on phase transition temperatures, thermal degradation, contact angles, pure gas permeabilities and permselectiv

ISSN:1042-7147    

DOI:10.1002/pat.1994.220050807

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractCarbon fibers were coated in situ with a thin film of polyhexamethylene adipamide by an interfacial polycondensation technique. The modified fibers were used for the preparation of epoxy‐based unidirectional composites. Specimens of these materials were immersed in water until equilibrium conditions were attained. The weight gain at equilibrium was determined as a function of the immersion temperature, the fiber volume fraction and the polyamide content deposited on the fibers. Water penetration in specimens made with uncoated carbon fibers increases when the volume fraction decreases. Introduction of the polyamide interlayer initially increases the water absorption, but reduces it at higher immersion temperatures and/or higher polyamide contents. The treated specimens were subjected to the short beam test to determine the interlaminar shear strength (ILSS). The data show that the ILSS decreases with water penetration but increases when the immersion temperature increases from 40 to 70°C. The overall performance encountered is discussed in terms of the possible roles of the polyamide interphase while taking into account mechanisms concerned with matrix plasticization, interphase degradation and residual stress relaxati

ISSN:1042-7147    

DOI:10.1002/pat.1994.220050808

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY