Unoriented Samples Research Articles

Effect of polypropylene morphology on thermal cis‐trans isomerization and photofading of some azo dyes: A kinetic study

AbstractFive polypropylene films were prepared having different crystallinity and morphology, the latter having been modified by stretching. They were colored with azo dyes XC6H4NNC6H4N(C2H5)2 (where XH, OCH3, CN, and NO2). The kinetics of the thermal cis‐trans isomerization of these dyes has been studied in the range 21–41°C, much above the glass transition temperature of the polymer. The isomerization process was found to be strictly first‐order; the kinetic parameter values have been correlated with the free volume extent in the amorphous regions of the matrix. Lightfastness of the dyes in the polymer matrices has been also investigated: It appeared to be more important for the unoriented samples with respect to the stretched ones and substantially independent on the crystalinity degree.

Critical current enhancement in field-oriented YBa2Cu3O7−δ

The crystalline anisotropy of YBa2 Cu3 O7−δ is found to have a significant effect in degrading critical current Jc . Pressed polycrystalline pellets of field-oriented grains have significantly higher Jc values (>5 times larger) than unoriented samples of the same material. Effects of annealing and metal doping are also discussed.

Two-dimensional multiple-quantum NMR spectroscopy of isolated half-integer spin systems. II. 35Cl examples

Two-dimensional double-quantum (2D2Q) 35Cl NMR spectra of systems exhibiting electric quadrupolar effects have been obtained. Single-crystal type spectra ( type a) result from magnetic field-oriented lyotropic liquid crystalline samples containing Cl − ions. Inhomogeneous powder patterns ( type b) result from unoriented lyotropic liquid crystalline samples. A homogeneous biexponentially relaxed spectrum ( type c) results from a sufficiently concentrated solution of a macromolecule in Cl −containing medium. The theory of the 2D2Q experiment on isolated spin-2 systems producing type a spectra has been elaborated. The effects of variation of the flip angle of the read pulse and offset of the excitation frequency have been derived. Experimental manifestations of these effects have been recorded. The recovery of the spectrum of an oriented lyotropic liquid crystalline sample after a sample rotation in the spectrometer magnetic field provides an example of transient, partial NMR invisibility in the one-dimensional single-quantum 35Cl NMR spectrum.

Optical reflectivity studies of magnetically oriented YBa_2Cu_3O_7−δ

The optical reflectivity spectra of magnetically oriented YBa2Cu3O7 −δ are reported over a wide energy range from 50 to 24 000 cm−1 (6 meV to 3 eV). A strong optical anisotropy is observed, with most phonon modes associated with the E ‖ c spectrum. An anisotropic effective-medium theory is used to permit direct comparison of these data with spectra from unoriented grains. The excitonic feature is found to be considerably more intense in the unoriented sample.

Orientation of α-helical peptides in a lipid bilayer

Samples of pure lipid (dipalmitoylphosphatidylcholine) and lipid containing short α-helical peptides were oriented and examined by X-ray diffraction, together with unoriented samples of pure peptide. X-ray reflections from the bilayer and the α-helices showed that the peptides had oriented in the bilayer with their helical axes perpendicular to the surface.

Preparation and 57Fe Mössbauer study of PrCo 3FeB, NdCo 3FeB, SmCo 3FeB and SmCo 2Fe 2B

PrCo 3FeB, NdCo 3FeB, SmCo 3FeB and SmCo 2Fe 2B were prepared by induction melting and studied by 57Fe Mössbauer effect at room temperature. Mössbauer spectra were recorded both on unoriented powder samples and on powders oriented in a 12 kOe magnetic field. SmCo 2Fe 2B and SmCo 3FeB, which contain Sm 3+ with positive Stevens coefficient α J , have an easy axis in agreement with magnetic measurements reported in the literature. On the contrary PrCo 3FeB and NdCo 3FeB, in which Pr 3+ and Nd 3+ have negative α J , are characterized by an easy plane. Mössbauer results indicate a strong preference of iron atoms for the axial 2c sites and an important anisotropy of their magnetic hyperfine structure.

Plastic deformation of poly(tetramethylene oxide). II. Molecular orientation as measured by x‐ray diffraction and NMR measurements

AbstractThe orientation of the crystalline and amorphous phases in uniaxially drawn samples of polytetramethylene oxide has been studied by x‐ray and NMR methods. Pole figure measurements give the orientation of the crystalline phase. Its dependence on the draw ratio does not obey the pseudoaffine model. The crystalline fraction is derived from NMR measurements at temperatures between Tg and Tm, where the free induction decay (FID) of the unoriented sample can be analyzed in terms of a rigid (crystalline), a constrained, and an amorphous phase. Low temperature (T < Tg) measurements of the NMR second‐moment anisotropy in protonated and deuterated samples give a mean orientation of the chains higher than that corresponding to the crystalline phase. The lack of anisotropy in the tail of the FID at temperatures between Tg and Tm indicates no appreciable anisotropy in the truly amorphous interlamellar phase. From this and from the ratio of the P4/P2 orientations, factors which obey the “most probable distribution,” it is concluded that the amorphous orientation is due to the layer of constrained chains at the surface of the lamellae.

Far infrared and submillimetre studies of the ferroelectric phase transition in (VF2-F3E) copolymers

Abstract Polarized transmission spectra of oriented (VF2-F3E) copolymer film were measured in the 8–500 cm−1 range for the VF2/F3E composition of 100/0, 80/20, 70/30 and 60/40 as a function of temperature in both ferroelectric and paraelectric phases. The spectra were evaluated to obtain the dielectric response function and absorption coefficient. In comparison with pure PVF2, the lowest-frequency mode at 73cm−1 splits in the copolymer samples into two components at ∼51–61 and ∼ 115 cm−1 which are assigned to Brillouin zone centre and boundary (Z-point) librational modes around the polymer chain axis with respect to the Brillouin zone of the ideal PVF2 crystal. The lower mode of this pair disappears in the paraelectric phase in agreement with selection rules for regular 50/50 copolymer. Higher-frequency modes do not strictly obey the selection rules because of compositional and dynamical disorder. In the submillimetre range, 8–30 cm−1, additional relaxation (over-damped oscillation) was found which is assigned to IR active standing acoustic waves within the lamellar crystallites broadened by their thickness distribution. Differences between the absorption in crystalline and amorphous phase are quantitatively evaluated for an unoriented sample.

Paleomagnetism and rock magnetism of Quaternary volcanic rocks and Late Paleozoic strata, VC‐1 core hole, Valles Caldera, New Mexico, with emphasis on remagnetization of Late Paleozoic strata

Paleomagnetic and rock magnetic data obtained from azimuthally unoriented core samples, collected at approximately 1‐ to 3‐m intervals, of Continental Scientific Drilling Program core hole VC‐1 have prompted reinterpretations of the Quaternary volcanic stratigraphy intersected by the bore and have aided in evaluating the thermal regime within late Paleozoic strata attending fluid circulation and mineral deposition during and after development of the Toledo and Valles calderas. The results from Quaternary units (Banco Bonito Obsidian: I = +35.4°, a95 = 2.8° (inclination only determinations), n = 33; Battleship Rock Tuff: D = 359.6°, I = +42.4°, a95 = 2.8°, n = 5 site means (surface sites); VC‐1 Rhyolite: I = +39.2°, a95 = 12.8°, n = 7; Upper VC‐1 Tuff: I = +37.2°, a95 = 10.7°, n = 13; Middle VC‐1 Tuff: I = +42.1°, a95 = 2.1°, n = 39; South Mountain Rhyolite: D = 350.9°, I = +49.9°, a95 = 3.4°, n = 10 (one surface site)) are consistent with isotopic age data, indicating that the entire moat volcanic sequence intersected is less than 650 kyr. Monitoring of natural remanent magnetization (NRM) intensity, NRM directions, directions of magnetizations isolated during progressive demagnetization, median destructive forces, and rock magnetization parameters has identified systematic variations within the thick Banco Bonito Obsidian and VC‐1 Tuff units. The Permian Abo Formation, Pennsylvanian to earliest Permian Madera Limestone, and Pennsylvanian Sandia Formation typically contain a moderate positive inclination magnetization component (Abo Formation: I = +52.2°, a95 = 7.4°, n = 16; Madera Limestone: I = +58.4°, a95 = 2.8°, n = 105; Sandia Formation: I = +53.9°, a95 = 4.8°, n = 21); when residing in magnetite, it is usually unblocked in the laboratory by 350°C; when carried by hematite it is unblocked by 550°C. A moderate negative inclination (e.g., Madera and Abo strata: D = 173.1°, I = −46.6°, a95 = 5.5°; n = 47 samples; assuming a north seeking positive inclination RM providing a useful means of core orientation), oppositely directed magnetization is occasionally isolated and removed at higher laboratory unblocking temperatures (up to 550°C in magnetite‐dominated and 600°C in hematite‐dominated lithologies). Where present, magnetizations of shallower inclination (e.g., Madera and Abo strata: D = 160.1°, I = −10.9°, a95 = 4.4°, n = 28) are removed over higher ranges of unblocking temperatures, and these are probably of late Paleozoic age. The moderate negative and positive inclination magnetizations are in all likelihood viscous partial thermoremanent magnetizations (TRMs) (VPTRMs). These were activated at moderate (∼300°C) temperatures between 1.45 and 0.97 Ma, attending and following the main stages of Toledo/Valles caldera development during the Matuyama, and at near‐present downhole temperatures (∼100°–180+ °C) during the Brunhes and possibly within the last 10 kyr, respectively. Importantly, the preservation of negative inclination RM components in magnetite‐dominated lithologies of the Madera Limestone dictates that temperatures during the Brunhes chron (past 730 kyr) did not exceed approximately 300°–350°C. The inferred temperatures for thermal activation of the VPTRMs, based upon the Middleton and Schmidt thermal activation curves for both magnetite and hematite derived following Walton, agree with independent estimates of thermal activity, using fluid inclusion and K‐Ar isotopic age determination data, during the Quaternary. The results further illustrate the potential usefulness of thermal activation theories for inferring temperatures of past geologic events, especially when they can be applied to magnetizations of similar age residing in both magnetite and hematite, and of paleomagnetic and rock magnetic studies in general in continuous coreholes in complex geologic environments.

X‐ray and optical investigations on polymers with mesogenic side groups

AbstractBased on polarisation microscopic observation of polymers with mesogenic side groups at the phase transition isotropic‐smectic, a domain‐like structure has to be assumed for smectic phases. Two different regular‐shaped nuclei are formed at the phase transition on slightly different conditions which grow after twinning into bǎtonnets. The Avrami equation can be applied for a quantitative description of the growth of the anisotropic areas as shown for one form of the nuclei. Unoriented and sheared samples maintain their morphology when cooled from the liquid‐crystalline to the partially crystalline phase. The crystalline phase of polymers with mesogenic side groups was investigated by X‐ray diffraction on differently oriented samples. It was found that the crystallites have the same internal structure despite the fact that they exhibit different uniaxial fibre axes. Optical investigations provide helpful supplementary information for deciding what kind of layered structure is present in the crystalline and smectic phase.

Conformational defects in Durham polyacetylene: photo-induced IR absorption

The authors report measurements of photo-induced absorption (PA) in the energy range 400-4500 cm-1 in samples of stretch-oriented and unstretched Durham route polyacetylene. Stretch-oriented samples show spectra very similar to those for Shirakawa polyacetylene, with the electronic 'midgap' absorption peaking at 3600 cm-1 (0.45 eV) and vibrational modes peaking at 520, 1287 and 1365 cm-1. Whilst the oriented films show that characteristics of long-chain polyacetylene, the unoriented samples are very disordered, with only short sections of straight polyene. Similar PA features are seen, but shifted to higher frequencies, with the electronic 'midgap' absorption peak at 0.55 eV. The relative strength of the vibrational model is reduced by a factor of two, indicating an increase in soliton mass by this factor. They consider that the chain bends, etc., that terminate the straight-chain sections increase the effective electron-phonon coupling which raises the pi - pi * gap 2 Delta 0 by 30% and the soliton mass ( varies as Delta 03) by 100%. The 'midgap' absorption is at an energy lower than Delta 0 by an effective electron correlation energy (of about 0.5 eV) and the authors find, in accord with recent calculations, that this varies linearly with Delta 0.

Apparatus for Measurement of Complex Shear Modulus of Liquid Crystals at Low Frequencies

An apparatus for measuring the frequency dependence of the complex shear modulus of liquid crystals as low as 102 dyn/cm2 at low frequencies (from 1 Hz to 1 kHz) was constructed, and was applied to the nematic and smectic A phase of 40.8 (butoxybenziliden-octylanine). The shear viscosity of unoriented multidomain sample in the smectic A phase showed a divergent behavior of 1/ω when the frequency went to zero. This anormalous behavior was interpreted in terms of the anharmonic effects associated with the thermal undulation of the smectic layers based on the theory of Mazenko, Ramaswamy and Toner.

ESR measurements in Durham polyacetylene

Polyacetylene prepared by the Durham precursor route can be obtained in a disordered form by thermal conversion of a solution-cast film of the precursor polymer, or in a highly oriented film by stretching the precursor film during the transformation reaction. We report the evolution of spins during transformation and isomerisation, and constrast the broad, temperature-independent ESR line (10 Gauss) obtained for unoriented samples (immobile defects) with the anisotropic, narrowed line obtained for stretch-oriented samples (at room temperature with B parallel to chains ΔH = 3 Gauss, with B perpendicular to chains, ΔH = 1.9 Gauss), indicative of mobile defects. The anisotropic linewidth is shown to agree quantitatively with that expected through the anisotropic part of the proton hyperfine interaction. The temperature dependence of the linewidth is described by a model with activated hopping along the chains.

On the sub-Tg annealing of uniaxially oriented and unoriented atactic polystyrene

DSC analysis was performed on uniaxially oriented and unoriented atactic polystyrene samples prior to and after annealing at 80 °C. With increasing annealing times, an endothermic peak appeared, whose area increased with the duration of the annealing period. No difference was found between the endotherm areas for the oriented and the unoriented polymer.

Dielectric Properties of Some Side Chain Liquid Crystalline Polymers

AbstractAn experimental setup to determine the anisotropic dielectric constants for liquid crystalline side chain polymers as function of the temperature and the frequency in the range between 100 Hz and 10 MHz is described. From the anisotropic dielectric data some more specific informations can be obtained comparing with the results obtained from unoriented samples. ‐ The anisotropic dielectric properties of two liquid crystalline side chain polymers containing the same polyacrylic main chain and slightly modified side chains are described in the glassy, nematic as well as in the isotropic state as function of temperature and frequency. For these compounds, three different relaxation processes are described. A process was found with the main component in ϵ∥ due to the relaxation of the mesogenic side chain around the main chain back bone. A broad relaxation process, near above the glass temperature, with the main component in ϵ⟂ is interpreted as due to diffusive motion of different dipoles. Another broad relaxation process occurs in the glassy state, containing parallel and perpendicular dipole components of the mesogenic ester group. In the isotropic state, the relaxation process is dominated by the parallel relaxation in the nematic state.

Pyroelectricity in Oriented Polytrifluoroethylene

Poling of oriented polytrifluoroethylene (PTrFE) was found to produce pyroelectricity which showed anomalous behavior and formation conditions identical to those in unoriented samples. The pyroelectric activity in oriented PTrFE was greatly enhanced when the poling temperature was low but was reduced as the poling temperature was raised, contrary to the behavior of ordinary thermoelectrets. The enhancement of the pyroelectricity is attributed to a greater increase of the new crystalline region and to the orientation effect, which aligned the dipoles along the electric field. The reduction of the pyroelectricity is attributed to an increase in the degree of chain orientation, which aligns the polar axis parallel to the film plane. This behavior depended strongly on the state of the amorphous region from which the new crystalline region carrying the spontaneous polarization grew.

Nematic Order in Polyesters with Flexible Moieties in the Main Chain

Properties of polyesters based on 4,4′-dihydroxy-2,2′-dimethylazoxybenzene and a homologous series of alkanedioic acids with methylene sequence length n=3—4 are discussed in the light of recent results based on DSC, PMR, magnetic birefringence and X-ray data. Influence of substitution in the mesogen and spacer is also described. Particular attention is given to the oddeven effect in the homologous series and the existence of two distinct levels of molecular order for the n=even and n=odd members of the series. On the basis of X-ray diffraction data performed on oriented samples, a cybotactic micellar model for the n=even polymers is proposed. The cooperative nature of the formation of cybotactic micelles is shown by the study of order parameter and its dependence on the degree of polymerization. Progressive development of layered order in n=even polymers with increase in molecular mass is also shown by SAX patterns of unoriented samples of poly(4,4′-dioxy-2,2′-dimethylazoxybenzenedodecanedioyl). While the Meier and Saupe theory of the nematic state is in good agreement with the S(T) dependence for noncybotactic polymer systems for most of the nematic interval, it diverges in the vicinity of the clearing point. In contrast to low molecular mass nematics, polymeric nematics show a remarkable stability at the clearing temperature and a large pretransitional interval.

Formation of Pyroelectricity in Unoriented Polytrifluoroethylene

Pyroelectricity in polytrifluoroethylene was studied in detail on unoriented samples. The pyroelectricity was found to be anomalous as regards the temperature dependence of the pyroelectric coefficient, since the latter changed signs twice over the temperature range 100 to 350 K. Also, the sample with the lowest initial crystallinity exhibited the greatest degree of pyroelectric activity. Crystallization coupled with poling was found to be responsible for the pyroelectricity, i.e., spontaneous polarization was induced in the new crystalline region developed during the poling process, and not in the existing crystalline region, because it is difficult for the main chain in the crystal to rotate. The spontaneous polarization was found to increase as the temperature was increased from 185 to 273 K, resulting in the anomalous pyroelectricity. A model analogous to ferrielectricity is proposed to explain this phenomenon.

Crystalline order and melting behavior of isotactic polypropylene (α form)

AbstractSamples of isotactic polypropylene in the α form may have different degrees of order in the up and down positioning of the chains. By suitable programming of the crystallization history of unoriented samples it is possible to show, from DSC and WAXS data, that a strict correlation exists between the melting behavior and the degree of ordering of the chains. The process of ordering at annealing temperatures above 150°C may lead to a “continuum” of modifications of the α form from less ordered to highly ordered ones; correspondingly we observe an increase in the melting point by as much as 15°C.

Magnetic properties of the Bay of Islands ophiolite suite and implications for the magnetization of oceanic crust

Rock magnetic properties, opaque mineralogy, and degree of metamorphism were determined for 101 unoriented samples from the North Arm and Blow‐Me‐Down massifs of the Bay of Islands ophiolite complex, Newfoundland. The weathered and metamorphosed extrusive basalt samples have a weak, secondary magnetization arising from oxidation and exsolution of ilmenite of unknown origin. The initial magnetization of the underlying sheeted dike complex appears to have been destroyed by hydrothermal alteration soon after formation. The magnetic intensity of the gabbroic samples increases as the degree of alteration increases, with the highly altered upper metagabbros having an average intensity of 3×10−3 emu/c3. Because magnetization of the metagabbro samples is related to nonpervasive, variable alteration, these crustal units are unlikely to make a significant contribution to lineated magnetic anomalies. A compilation of our results and other studies suggests a model in which oceanic crust magnetization results from an upper extrusive basalt source layer, roughly 600 m thick, with no contribution from a deeper source layer recognizable from these Bay of Islands data.