摘要:

The effect of uniaxial drawing on orientation of the crystalline fraction of two polymers forming hydrogen bonds, nylon-6 and nylon-11, has been investigated using X-ray diffraction. These two polymers have similar crystal phases, although their hydrogen bond density differs. For both polymers, the deformation occurs in two steps, the first being a plastic deformation of the &agr;-phase spherulites. This leads to two populations of crystals, one with the chain axis oriented parallel to the draw direction, the second with theaaxis (hydrogen bond direction) aligned along the draw direction. In the second step, thea-axis aligned population gradually tilts, leading to a uniaxial orientation of the samples with chain axis aligned along the draw direction. For nylon-11, the onset of this step corresponds to the emergence of crystals of the &ggr; phase, which rapidly becomes the major phase. It reaches a higher orientation than the &agr; phase, and stems from crystallization upon tension of the polymer. For nylon-6, although the &ggr; phase also appears during drawing, at the maximum draw ratio only a small fraction is present. This difference is attributed to the relative stability of the two phases, which is different for nylon-6 than for nylon-11.Key words: orientation, X-ray diffraction, nylon, hydrogen bonds.

ISSN:0008-4042    

DOI:10.1139/v98-121

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The stratum corneum, the top layer of the epidermis, is the material that constitutes the membrane enveloping our body. The lipids that are present are responsible for the permeability properties of the skin and, as a consequence, are essential to maintain the hydration of the internal components and to protect our body from external agents. In the present work, the mixing and the structural properties of model mixtures formed by the main lipids of the stratum corneum have been examined by infrared spectroscopy. The model is formed by an equimolar mixture of ceramides (type III), cholesterol, and perdeuterated palmitic acid. Binary mixtures as well as mixtures for which the ceramides were substituted by sphingomyelin, a ceramide precursor, have also been studied. The results indicate that the stratum corneum model mixture exhibits a rich polymorphism, ranging from crystalline domains with heterogeneous lipid composition and orthorhombic chain packing, to a fluid and homogeneous phase. To obtain this particular behaviour, the three components are essential and the specific role of each species is discussed. In addition, the results reveal that the homogeneous lipid distribution observed for temperatures higher than 70°C can be maintained at low temperatures, leading to the formation of a metastable phase. Several weeks are needed to obtain the thermodynamically stable phase if the sample is incubated at 5°C. However, it is rapidly induced by annealing the sample at 40°C.Key words: stratum corneum, lipid, infrared spectroscopy, cerami

ISSN:0008-4042    

DOI:10.1139/v98-114

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Wideline deuterium nuclear magnetic resonance was used to investigate the phase behaviour of bi layer dispersions of chain-perdeuterated dipalmitoylphosphatidylcholine (DPPC-d62) and DPPC-d62containing 28.5 mol% cholesterol for temperatures between 0°C and 90°C and pressures from ambient to 270 MPa. Spectra were obtained over a range of temperature at ambient pressure, 100 MPa, and 210 MPa and over a range of pressure at fixed temperatures of 0°C and 45°C (40°C for the sample containing cholesterol). The combination of complementary isobaric and isothermal scans produced observations that suggest two possible refinements to previously reported DPPC-d62pressure-temperature phase diagrams. In contrast to DPPC-d62, which displays at least three transitions as temperature is lowered from 90°C to 0°C at a fixed pressure of 210 MPa, the sample containing 28.5 mol% cholesterol displayed a continuous change from fluid to ordered over a wide temperature range for 210 MPa and below. These observations suggest that pressure does not induce any substantial repositioning of cholesterol in the bi layer over the range of conditions studied and that cholesterol reduces the sensitivity of bilayer properties to pressure.Key words: deuterium nuclear magnetic resonance, model membrane, high pressure, cholesterol, phase tran

ISSN:0008-4042    

DOI:10.1139/v98-116

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The synthesis of Ru2(&mgr;-O2CR)4(&mgr;´-O2CR)(1), R = -CH2(CH2)6CH=CH(CH2)5CH3, has been achieved and characterization using elemental analysis and FTIR and UV-Vis spectroscopies undertaken. Strong evidence for a hexagonal discotic mesophase has been found using differential scanning calorimetry, variable-temperature polarizing optical microscopy, and X-ray powder diffraction. A solid to liquid crystal transition was found upon heating at 128°C and the mesophase is found to persist to room temperature upon cooling from 150°C. This is the first report of room temperature mesomorphism in a mixed-valent metallomesogen.Key words: ruthenium carboxylate, liquid crystal, metallomesogen, mixed valence, polyme

ISSN:0008-4042    

DOI:10.1139/v98-105

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Electrically conducting poly[E-1,2-(4,4prime-dihexyl-2,2prime-dithienyl)ethylene] was synthesized and structurally characterized by UV-visible,1H NMR, and FTIR spectroscopy. The head-to-head arrangement of the alkylthiophene dyads directly affects the UV-visible, photoluminescence, and electroluminescence maxima of the polymer. The conductivity of the doped polymer was measured to be ~2 S cm-1and the stability of the oxidized polymer possessing various dopants was compared. UV-visible irradiation of PDHDTE rendered the films insoluble and photolithography was used to produce micron-size images. FTIR was used to monitor the photoproducts during photolysis of PDHDTE. Mechanisms of photooxidation were proposed, based on the photoproducts observed.Key words: polythiophene derivative, head-to-head dyad, photolithography, photooxidation, electroluminescence.

ISSN:0008-4042    

DOI:10.1139/v98-110

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The reaction of Mn(II), Zn(II), and Ni(II) perchlorate with 1,2-bis(4-pyridyl)ethane (bpe) was studied and the products were characterized by IR spectroscopy and X-ray diffraction methods. The zinc and nickel compounds are isomorphous with a metal-bpemolar ratio of 1:4, while the manganese compound is quite different with a Mn-bperatio of 1:5. [Mn(&mgr;-bpe)(H2O)4](ClO4)2·4(bpe)·2H2O (1) is monoclinic,C2/c,witha= 30.141(7),b= 13.993(4),c= 19.765(4) Å,&bgr;= 129.41(1)°, andR= 0.059. The Mn atom is located on an inversion centre and forms an infinite chain with the bridgedbpeligand. The four otherbpemolecules are hydrogen-bonded to the aqua ligands and form an extensive H-bonded interpenetrating 3D network. The bonds Mn-N = 2.316(3) Å and Mn-OH2= 2.148(4) and 2.178(3) Å. [Zn(&mgr;-bpe)(bpe)2(H2O)2](ClO4)2·bpe·H2O (2) crystallized in theP21/cspace group, witha= 14.609(4),b= 21.164(5),c= 16.482(5) Å,&bgr;= 114.69(2)°, andR= 0.058. For [Ni(&mgr;-bpe)(bpe)2(H2O)2](ClO4)2·bpe·H2O (3),a= 14.511(6),b= 21.216(7),c= 16.467(7) Å,&bgr;= 114.76(3)°, andR= 0.065. The aqua ligands are locatedtransto each other. The bridgedbpeligands form an infinite chain with the metal atoms. Two other terminalbpeligands are coordinated to the metal intranspositions to each other. These ligands form H-bonds with the aqua ligands of other chains resulting in an H-bonded 3D network. The Zn-N distances vary from 2.151(3) to 2.185(4) Å while the Ni-N bonds are between 2.098(10) and 2.126(11) Å. The bonds Zn-OH2= 2.125(4), 2.161(4) Å and Ni-OH2= 2.077(11), 2.110(11) Å.Key words: crystal structure, manganese complex, zinc complex, nickel complex, 1,2-bis(4-pyr

ISSN:0008-4042    

DOI:10.1139/v98-130

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The ternary cobalt germanium pnictide systems CoGexPn1-x(Pn= P, As, Sb; 0 <x<1) were investigated. The ternary phosphides CoGexP1-xand arsenides CoGexAs1-xadopt the MnP structure (Pnma) in the range 0 <x<0.8, with Ge andPn(Pn= P, As) disordering over the anion sites. Reactions in the antimonide system CoGexSb1-xresult in a mixture of ternary phases, one with the NiAs structure (P63/mmm) in which Ge and Sb disorder over the anion sites, and another that is a new intermetallic compound, Co3Ge2Sb. Single-crystal X-ray diffraction reveals that Co3Ge2Sb crystallizes in the hexagonal space groupP6/mmmwitha= 8.9128(13) Å,c= 7.6312(8) Å, andZ= 6 (T= 22°C). The structure of Co3Ge2Sb comprises alternating kagomé nets of Co atoms and 63nets of Ge atoms, with Sb2pairs stuffed along the centres of the concentric hexagons of these nets. Co3Ge2Sb may be regarded as an intermediate structure that is distorted from the limiting CoSn and CaCu5structures.Key words: cobalt, germanium, antimony, pnictide, crystal struc

ISSN:0008-4042    

DOI:10.1139/v98-142

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The orientation behavior of liquid crystal molecules in stretched films of polymer-dispersed liquid crystals (PDLC) was investigated by means of infrared dichroism. The liquid crystal used is 4prime-octyl-4-biphenyl-carbonitrile (8CN); the polymer matrices are semicrystalline poly(epsilon-caprolactone) (PCL) and an amorphous miscible blend of PCL with poly(vinyl chloride) (PVC). 8CN was found to have a limit of solubility below 5 wt.% in PCL. We show that an uniaxial stretching can effectively induce a macroscopic orientation of 8CN, and that this orientation can be preserved in the films after removal of the extensional force at room temperature, where 8CN is in its liquid crystalline phase. The molecular orientation is obtained even by stretching PDLC films with 8CN in the liquid state. These results suggest that an elongated polymer cavity in stretched PDLC imposes LC director fields with respect to the long axes of the droplets, which are aligned parallel to the strain direction. The experiments also reveal that the orientation of 8CN is higher in stretched PDLC with a semicrystalline matrix (PCL) than with an amorphous matrix (the PCL-PVC blend), and that the sizes of the LC droplets also have a slight effect on the induced orientation. This work represents a first step in the exploration of new electrooptical effects of PDLC through the presence of a uniform orientation of the liquid crystal molecules and modifications of the polymer cavity at the electrical field-off state.Key words: polymer-dispersed liquid crystals, molecular orientation, infrared dichroism, electrooptical materials.

ISSN:0008-4042    

DOI:10.1139/v98-141

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The interaction and reaction of PCl3and PCl3-H2S mixtures with the microporous materials Silicalite, ALPO-5, NaY, NaX, and NaA have been investigated, with the intention of producing phosphorus sulfide clusters in the pores. A rich chemistry was observed and monitored by solid state31P NMR. The presence of P4S3, &agr;-P4S5, &bgr;-P4S6, and P4S7inside the NaY &agr;-cages was demonstrated, as well as a new species that is possibly a third geometric isomer of P4S4withC3vsymmetry.129Xe NMR showed the exclusion of Xe from the micropores by the phosphorus sulfides. Sulfides lower than P4S7are small enough that they undergo rapid pseudo-isotropic reorientation inside the NaY &agr;-cage.Key words: phosphorus sulfides, intrazeolitic cluster synthesis.

ISSN:0008-4042    

DOI:10.1139/v98-147

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The phase content of a low-density polyethylene was studied by analysis of the CH2rocking vibrations in non-oriented films prepared from the press (P-films) or from solution (S-films). Spectral simulations of the transmission spectra give the mass fractions of the orthorhombic phase &agr;orthoand of two noncrystalline phases (monoclinic-like and amorphous). The values of &agr;ortho(IR) are compared to &agr;ortho(i) where (i) stands for the X-ray diffraction, density, and DSC techniques. New results are obtained concerning the orthorhombic order and the change of phase content with aging. A two-phase analysis is justified for non-aged films containing a small amount of the monoclinic-like phase. The values of &agr;ortho(IR) are larger than &agr;ortho(i), the difference ranging between 0.12 and 0.43. The difference is a measure of the short-range order. &agr;ortho(IR) can reach 0.73 for the S-films. The stability of the short-range order phase is investigated. The sample is also analyzed using the trace of slow calorimetry. The difference between &agr;orthoby DSC and by slow calorimetry is a measure of strainable order. During aging, the variation in the phase content is large for the noncrystalline phases (in content and frequency) and small for the orthorhombic. The increase of the monoclinic-like phase during aging suggests that it is a precursor of the more stable orthorhombic organization. The quantification of two noncrystalline phases on fresh and aged films clarifies some ambiguity found in the literature about the monoclinic-like phase and the localization of bands in the rocking region for sample characterization. Analysis of other regions of the spectrum is needed to confirm the present results.Key words: low-density PE, phase content, FTIR, network phase, slow calorimetry.

ISSN:0008-4042    

DOI:10.1139/v98-159

出版商:NRC Research Press    

年代:1998

数据来源: NRC