Dielectric relaxations and molecular motions in poly(vinylidene fluoride) with crystal form II

Molecular motions in poly(vinylidene fluoride) were studied by dielectric measurements. Of the three relaxation processes, the α_a and the α_c were studied. The α_a relaxation was attributed to the molecular motions in the amorphous regions and the α_c relaxation to molecular motions in the crystalline regions and their surfaces. The relaxation time and the magnitude of the α_a absorption were analyzed on the basis of the Adam-Gibbs theory of the temperature dependence of the size of the cooperatively rearranging region. As a result it was concluded that the molecular structure of crystal form II holds locally, even in the amorphous regions. The relaxation time and the magnitude for the α_c absorption were analysed on the basis of the two-site model. It was concluded that the α_c relaxation is attributable not only to molecular motions in the folds of the lamellar crystals, but also to those in the interior of the crystal; the folded chain is relatively mobile, while the molecular chain in the interior of the crystal executes restricted rotation around the chain axis.     

Dielectric relaxation and molecular motion in poly(vinylidene fluoride)

The dielectric properties of poly(vinylidene fluoride) have been studied in the frequency range 10 Hz to 100 kHz at temperatures between ?196 and 150°C. Three dielectric relaxations were observed: the α relaxation occurred near 130°C, the β near 0°C, and the γ near ?30°C at 100 kHz. In the α relaxation the magnitude of loss peak and the relaxation times increased not only with increasing lamellar thickness, but also with decrease of crystal defects in the crystalline regions. In the light of the above results, the α relaxation was attributed to the molecular motion in the crystalline regions which was related to the lamellar thickness and crystal defects in the crystalline phase. In the β relaxation, the magnitude of the loss peak increased with the amount of amorphous material. The relaxation times were independent of the crystal structure and the degree of crystallinity, but increased slightly with orientation of the molecular chains by drawing. The β relaxation was ascribed to the micro-Brownian motions of main chains in the amorphous regions. The Arrhenius plots were of the so-called WLF type, and the “freezing point” of the molecular motion was about ?80°C. The Cole-Cole distribution parameter of the relaxation time α increased almost linearly with decreasing temperature in the temperature range of the experiment. The γ relaxation was attributed to local molecular motions in the amorphous regions.     

The effect of pressure on the volume and the dielectric relaxation of linear polyethylene

The effects of pressure on the α (ca. 70°C, 1 kHz) and γ (ca. ?100°C, 1 kHz) relaxations of linear polyethylene were studied dielectrically between 0 and 4 kbar. Equation of state (PVT) data were also determined in the range of interest of these relaxations. The sample was rendered dielectrically active through oxidation (0.8 C?0 per 1000 CH₂). The α process (which occurs in the crystalline fraction) could be studied over a much wider temperature range than heretofore possible due to the effect of pressure in increasing the melting point. Examination of relaxation strength from 50 to 150°C showed that there must be two crystalline relaxation processes: the well-known α relaxation plus a competing one. The α relaxation is believed to be due to a chain twist–rotation–translation mechanism that results in rotation–translation of an entire chain in the crystal. The relaxation strength of the α process decreases and therefore indicates the presence of a second (faster and not directly observed) process that increases in intensity with increasing temperature. It is postulated that the second process is due to motion of defects that become more numerous through thermal injection at higher temperatures. Analysis of the relaxation data along with the PVT data allowed the constant volume activation energy for the α relaxation to be determined. It was found to be 19.4 ± 0.5 kcal/mole. The constant volume activation energy is important in modeling calculations of the crystal motions and is significantly smaller than the atmospheric constant pressure activation energy of 24.9 kcal/mole. The effect of pressure on the activation parameters and shape of the γ process was also determined. There has been controversy over whether the γ process occurs only in the amorphous fraction or in both the amorphous and crystalline phases. Since the two phases have quite different compressibilities, increasing the pressure should change the shape of the loss curves (versus frequency and temperature) if the process occurs in both phases. The shape (but not location) of the loss curves was found to be remarkably independent of pressure. This finding strengthens the view that the γ process is entirely amorphous in origin.     

Carbon-13 NMR distinction between categories of molecular order and disorder in cellulose

Differences between values of proton rotating-frame spin relaxation time constants can be exploited to separate a solid-state¹³C NMR spectrum of cellulose into subspectra of crystalline and noncrystalline regions. Variations in chemical shifts and¹³C spin-lattice relaxation time constants can then be used to study variations in molecular order and disorder within each of the two broader categories. Mechanical damage during Wiley milling increases the content of noncrystalline cellulose and changes the nature of molecular disorder within that category. Resolution enhancement of the subspectrum assigned to crystalline cellulose reveals pairs of signals at 83.9 and 84.9 ppm (cellulose I) or 86.8 and 88.3 ppm (cellulose II) assigned to C-4 on well-ordered crystal surfaces. A broader peak in the subspectrum of crystalline cellulose I is assigned to poorly-ordered surfaces. Relative proportions in Avicel microcrystalline cellulose were estimated as: 54% in crystal interiors, 22% on well-ordered surfaces, 8% on poorly-ordered surfaces, 16% in domains of disorder extending more than a few nanometres.     

Time-resolved infrared spectroscopic study of the orientation behavior of liquid crystalline molecules in the presence of an electric field

Time-resolved Fourier-transform infrared spectroscopy is used to follow the changes induced by electric field in molecular orientation of a 4-n-pentyl-4′-cyanobiphenyl (5CB) liquid crystal. At an electric field strength greater than 600 V cm^?1, the long axis of a 5CB molecule orientates to the direction of the electric field. The orientation function, however, saturates at a field strength greater than 1000 V cm^?1. The relaxation time of the rise amd decay processes was in the range of 0.04–0.24 s and a decreased with increasing field strength. The orientation/relaxation process is discussed on the basis of the motion of liquid crystal domains.     

A dielectric study of molecular relaxation in oxidized and chlorinated polyethylenes

A study was made of the dielectric relaxation in polyethylenes rendered dielectrically active through oxidation (0.5–1.7 carbonyls/1000 CH₂) and chlorination (14–22 Cl/1000 CH₂). Both linear and branched polymers were studied. All of the relaxations between the melt and ?196° were studied in the frequency range 10 Hz to 10kHz (100 kHz in the chlorinated samples). In the linear samples a wide range of crystallinities was studied (55% in quenched specimens to 95% in extended-chain specimens obtained by crystallization at 5 kbar). As is consistent with its being a crystalline process, the α peak was found to discontinously disappear on melting of the samples and reappear on recrystallizing on cooling. The disappearance of the smaller crystals before the larger ones appeared to be evident in the isothermal loss versus frequency curves. The relaxation strength of the α process increases with crystallinity. The measured relaxation strength is less than that expected on the basis of direct proportionality to the crystalline fraction with full contribution of all dipoles in the crystalline material. However, the intensity is not sufficiently low for the process to be interpreted in terms of reorientation of localized conformational defects in the crystal. The variation of intensity with crystallinity is best interpreted in terms of full participation of crystalline dipoles but with selective partitioning of both carbonyls and chlorines favoring the amorphous domains. A strong correlation of the α loss peak location (T_max at constant frequency or log f_max at constant T) with crystallinity for both carbonyl and chlorine containing polymers was found. This variation is interpreted in terms of chain rotations in the crystal where the activation free energy depends on crystal thickness. The dependence of log f_max and T_max on lamellar thickness as well as a comparison with the loss peaks of ketones dissolved in parafins indicates that the chain rotation is not rigid and is accompanied by twisting as the rotation propagates through the crystal. In agreement with previous studies the β process is found to be strong only in the branched polymers but can be detected in the chlorinated linear polymer. The β process was resolved from the α in the branched samples by curve fitting and its activation parameters determined. The γ relaxation peak in oxidized polymers including its high asymmetry (low-temperature tail) and increasing ε_max with increasing frequency and temperature when plotted isochronally can be interpreted in terms of a simple nearly symmetrical relaxation time spectrum that narrows with increasing temperature. No increase in relaxation strength with temperature was found. The chlorinated polymers behave similarly but appear to have some Boltzmann enhancement (450–750 cal/mole) of relaxation strength with temperature. The dependence of relaxation strength on crystallinity indicates that the process is an amorphous one. Further, no evidence of relaxation peak shape changes with crystallinity that could be interpreted in terms of a crystalline component in addition to the amorphous one was found. The comparison of the γ relaxation strength with that expected on the basis of full participation of amorphous dipoles indicates that only a small fraction (～10% in oxidized linear polymers) of them are involved in the relaxation. Thus it would seem that a glass–rubber transition interpretation is not indicated but rather a localized chain motion. It is suggested that the γ process, including its intensity, width, and activation parameters, can be interpreted in terms of an (unspecified) localized conformational (bond rotation) motion that is perturbed by differing local packing environments. The thermal expansion lessens the effects of variations in packing and leads to narrowing with increasing temperature. The conformational motion itself leads to increase in thermal expansion and hence a transition in the latter property. Some previously proposed localized amorphous phase conformational motions appear to be suitable candidates for the bond rotation motion. A weak relaxation peak found at temperatures below the γ and at 10 kHz may possibly be the dielectric analog of the δ cryogenic peak found previously mechanically at lower frequencies.     

Nuclear magnetic relaxation and molecular motion in poly(vinylidine fluoride)

Pulsed NMR T₁, T₂, and T_1ρ measurements are reported for poly(vinylidine fluoride) (PVF₂). The results demonstrate clearly the presence of four relaxation processes, three amorphous and one crystalline. The α relaxation is undoubtedly a crystalline one, while β and γ are both amorphous, in agreement with earlier conclusions from dielectric and dynamic mechanical measurements. The fourth relaxation (β′) observed initially in the mechanical measurements of Kakutani, but undetected in dielectric experiments, has been confirmed in our results and the process is described by an activation energy of 15.1 kcl/mole. Motion of folds on the surface of crystal lamellae is deemed to be the responsible mechanism for the β′ relaxation. Two models have been considered in the interpretation of the α process; rotation of crystalline chains in the vicinity of defects and rotational oscillation of restricted amplitude of all crystalline chains about the main chain axes. Rotation of amorphous chains is a possible mechanism for the γ process while motions of a general nature are responsible for the β relaxation. Our experimental results again indicate that spin diffusion plays an important role in the overall NMR response of the polymer.     

NMR study of molecular motion in oriented long-chain alkanes. II. Oriented mats of polyethylene single crystals

Measurements of the NMR second moment of a uniaxially oriented sample of polyethylene single crystals in the range of temperatures from ?196°C to 130°C and its dependence on the alignment angle γ between the orientation axis (preferential direction of the molecular chains) and the NMR magnetic field are presented. The experimental results are discussed mainly with respect to the high temperature relaxation, called the α process, in polyethylene. They are compared to theoretical predictions made for a number of mechanisms of molecular motion in Part I of this work. Only one of the mechanisms considered is found to be in quantitative agreement with experiment, the mechanism here referred to as flip-flop motion. This consists of thermally activated rotational jumps of the crystalline chain segment between folds around its axis between two equilibrium sites in the lattice. Each rotational jump through 180° is accompanied by a shift of the molecule along its axis by one CH₂ group. The discussion of the low-temperature relaxation of polyethylene, the γ process, is based partly on the above measurements and partly on measurements of second moments for unoriented polyethylene samples varying widely in morphology and noncrystalline content. The decrease of the second moment observed with these samples between ?196°C and 20°C is taken as a measure of the intensity of the γ process. A linear correlation is found between the decrease in the second moment, designated ΔS, and the noncrystalline content, 1 ? α_m; this can be represented by ΔS = 1.4 + 22.1(1 ? α_m). It is shown that neither the crankshaft mechanism not the kink mechanism is able to account quantitatively for this result. The model of a chain end moving in a vacancy fails to adequately describe the angle dependence of ΔS in oriented polyethylene single crystals. The “sandwich model” of a polyethylene single crystal, in which the crystalline core is covered by noncrystalline surface layers, is in better agreement with observations.     

Anisotropic Change in the Magnetic Susceptibility of a Dynamic Single Crystal of a Cobalt(II) Complex

Atypically anisotropic and large changes in magnetic susceptibility, along with a change in crystalline shape, were observed in a Co^II complex at near room temperature. This was achieved by combining oxalate molecules, acting as rotor, and a Co^II ion with unquenched orbital angular momentum. A thermally controlled 90° rotation of the oxalate counter anion triggered a symmetry‐breaking ferroelastic phase transition, accompanied by contraction–expansion behavior (ca. 4.5 %) along the long axis of a rod‐like single crystal. The molecular rotation induced a minute variation in the coordination geometry around the Co^II ion, resulting in an abrupt decrease and a remarkable increase in magnetic susceptibility along the direction perpendicular and parallel to the long axis of the crystal, respectively. Theoretical calculations suggested that such an unusual anisotropic change in magnetic susceptibility was due to a substantial reorientation of magnetic anisotropy induced by slight disruption in the ideal D ₃ coordination environment of the complex cation.     

The influence of gamma radiation on the dielectric relaxation behaviour of isotactic polypropylene: The α relaxation

The high-temperature α relaxation in gamma irradiated isotactic polypropylene (iPP) was studied over the temperature (298-406 K), frequency (10³-10⁶ Hz) and absorbed dose (0-700 kGy) ranges by means of dielectric spectroscopy. The multiple α relaxation was resolved from the β relaxation by curve fitting and its parameters were determined. Its position, intensity and activation energy were found to be strongly dependent on the changes in the structural and morphological parameters attributed to the exposure of the samples to radiation. Wide angle X-ray diffraction (WAXD) was used to investigate radiation-induced changes in the crystalline structure and degree of crystallinity, since this relaxation is connected with the crystal phase. Infrared (IR) spectroscopy and gel measurements were used to determine the changes in the oxidative degradation and the degree of network formation, respectively; the polar (carbonyl and/or hydroperoxide) groups that were introduced by irradiation were considered as tracer groups. Conclusions derived according to different methods were compared. The results reveal uncommon α relaxation behaviour with gamma radiation and confirm the multiple nature of this process, together with high dielectric and/or relaxation sensitivity of iPP to the radiation-induced changes.     

Structure and mechanical properties of poly(L‐lactic acid) crystals and fibers

The elastic constants of poly(L ‐lactic acid) (PLLA) crystals are reported on the basis of a commercial software package and the published crystal structure of the α form. A chain modulus of 36 GPa and a shear modulus of 3 GPa have been obtained for cylindrically symmetric aggregates of perfectly oriented crystals. The helical conformation of the PLLA molecule reduces the stiffness in the chain axis direction because bond rotation plays a significant role in the deformation. X‐ray crystal strain measurements suggest that shear of the α crystal parallel to the helix axis is the easiest mode of deformation, in agreement with the expectations obtained from the low shear modulus of 3 GPa obtained from the theoretical calculations. A combination of small‐ and wide‐angle X‐ray scattering, differential scanning calorimetry, dynamic mechanical thermal analysis, and shrinkage measurements has been used to characterize the structure that develops and the crystal transformation that occurs during fiber processing. The structure that develops during processing very much depends on the crystal transformation, and a structural model is proposed for fibers at different degrees of plastic deformation. The transformation of the α crystal into the β form and vice versa is governed primarily by shear along the helix axis because the chains must shear past each other during the crystal transformation, disrupting the lamellar packing. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 892–902, 2007     

A two-dimensional iron(II) carboxylate linear chain polymer that exhibits a metamagnetic spin-canted antiferromagnetic to single-chain magnetic transition

A two-dimensional iron(II) carboxylate coordination polymer, [Fe(pyoa)2]infinity, where pyoa is 2-(pyridin-3-yloxy)acetate, has been prepared by hydrothermal synthesis. Its crystal structure reveals a single iron(II) site with an elongated octahedral coordination environment containing four equatorial carboxylate oxygens and two axial pyridyl nitrogens; the iron(II) sites are linked by syn-anti micro-carboxylates to form chains along the b axis that have an Fe...Fe separation of 4.910 A. The shortest interchain and interlayer Fe...Fe distances are 6.453 and 11.125 A, respectively. The 4.2-295 K M?ssbauer spectra of [Fe(pyoa) 2] infinity consist of a single paramagnetic high-spin iron(II) quadrupole doublet. The axial Fe-N bond direction defines the Jahn-Teller axis at an iron(II) site and, consequently, the orientation of the single-ion magnetic anisotropy. Thus, along the b axis in a given chain, the spins are collinear and parallel to the Jahn-Teller axis. The Jahn-Teller axes of adjacent intralayer chains have different orientations with an angle of 79.2 degrees between the axes in adjacent chains in a bc layer. [Fe(pyoa)2]infinity exhibits field-induced metamagnetic behavior such that, in an applied field smaller than the critical field, the iron(II) spin-canted moments experience intrachain ferromagnetic interactions and weak interchain antiferromagnetic interactions; the spin canting yields weak ferromagnetism. In an applied field larger than the critical field, the weak antiferromagnetic interchain interactions are overwhelmed to yield superparamagnetic-like slow-magnetic relaxation with an energy barrier of 23(3) K. Single-crystal magnetic studies reveal a quasi-uniaxial magnetic anisotropy with the a axis as the easy-magnetic axis and the b axis as the hard-magnetic axis; the susceptibility measured along the easy a axis may be fit with the Glauber model to yield an effective intrachain exchange coupling constant of 2.06(8) K. A dynamic analysis of the susceptibility yields a 6.3(1) K energy barrier for intrachain domain wall creation. The observed field-assisted superparamagnet-like behavior is consistent with the dynamics of a single-chain magnet. Thus, [Fe(pyoa)2]infinity is best considered as a "metamagnetic-like" single-chain magnet.     

Mechanical relaxations in trans-1,4-polyisoprene crystals

Dynamic mechanical relaxation spectra were obtained for solution-grown crystals of trans-1,4-polyisoprene (TPI) in the α and β form. For single crystal mats three relaxations were observed. The highest temperature relaxation peak was characterized as due to the crystalline regions, whereas the intermediate peak was assigned to the primary amorphous relaxation which originates from the fold regions. The nature of the amorphous regions was elucidated by examining the effect of epoxidation on the lamellar fold surface. For an epoxidized single crystal mat, the intermediate relaxation maximum shifted to a higher temperature which corresponds to the glass transition of the almost completely epoxidized TPI. These results are discussed in terms of the fold structure of the TPI single crystals.     

Preferential uniplanar orientation mechanism of the (101) crystal plane of regenerated cellulose

The molecular orientation behavior of regenerated cellulose, in both crystalline and noncrystalline phases, was investigated quantitatively under various conditions during coagulation-regeneration from viscose solution and during drying of the resulting gel film. It was concluded that the stronger the tensions which arise parallel to the film surface during coagulation-regeneration and drying of the gel film, the more prominent become the uniplanar orientation of the (101) crystal plane and planar orientations of the crystal b axis and noncrystalline chain segments, all parallel to the film surface and associated with considerable distortion and disintegration of the regenerated crystal. This conclusion suggests an orientation mechanism of the cellulose II crystal, namely, rotation of the crystal around the U_{(101 )} axis associated with slippage of the (101) crystal plane, the most highly hydrated and most readily dislocated plane, in the direction of the tension, which is also parallel to the surface of the film. The behavior of this type of uniplanar orientation of the (101) crystal plane is characterized semiquantitatively by comparing observed distributions of the orientation of crystallographic axes with those calculated on the basis of a relatively simple model for crystal orientation.     

Strain- and temperature-induced polymorphism of poly(dimethylsiloxane)

Phase behavior of silica-filled poly(dimethylsiloxane) (PDMS) network was investigated by wide-angle X-ray diffraction (WAXD) under various strain ratio between room temperature and ?100 °C, and anomalous polymorphic behavior was discovered. At room temperature, when sufficient strain was applied, PDMS network was found to transform into the mesomorphic phase from which only a pair of sharp equatorial reflections and faint meridional scattering were obtained in the WAXD pattern. At low temperature, PDMS network crystallized into one of three different crystal forms according to strain ratio. These crystal forms were denoted as α, transient, and β forms in the descending order of corresponding strain ratio. The mesomorphic phase at room temperature transformed into the crystalline α form by reducing temperature. There was an anomalous feature about the transition of the crystalline forms that the position of reflections in the WAXD pattern changed continuously and reversibly with strain between the α and the β forms through the transient form, while keeping the diffraction angles almost unchanged.     

The effect of melt drawing ratio on the crystal structural change and performance of polyketone extrusion cast film

In this paper, the polyketone (POK) extrusion cast film is manufactured by melt stretching method, and the evolution process of the crystal morphology and mechanical properties with the increase of melt drawing ratio (MDR) are followed. The results show that the melt stretching process produces many micro shish-kebab crystals in the POK. The length of the shish crystal and the thickness of the kebab crystal hardly increase with MDR, but the lateral length of the kebab crystal shows linear growth when MDR exceeds 40. The crystalline morphology of POK is mainly affected by melt relaxation. The molecular chain has sufficient relaxation during cooling at a low MDR (20–40). At this time, micro shish-kebab crystals are mainly randomly arranged. When MDR exceeds 40, the rapid melt stretching shortens the relaxation time of the tie chain between the neighborhood shish crystal, and the atomic force microscopy image shows a typical shish-kebab structure. This experimental result indicates that the formation of the oriented lamella structure may be related to the relaxation of the molecular chains between the micro-shish. When the length of the shish axis and the thickness of the kebab lamellae are similar, it is difficult to distinguish the two.     

The influence of layer curvature on switching in ferroelectric B2 phases of liquid crystals having bent-shape molecules

In the B₂ phase of liquid crystalline compounds with bent-shape molecules ferroelectric switching can occur either by molecular rotation on the cone or by rotation of the molecule about its long axis (so-called chirality flipping), or by both mechanisms simultaneously. When the smectic layers of the B₂ phase are non-deformed and parallel the rotation of molecules under an external electric field occurs readily on the surface of the cone, while rotation around the long molecular axis is hindered by an energy barrier. Imposed deformation of smectic layers leads to interaction between local layer curvatures and molecular orientation, which results in the energy barrier hindering the molecular rotation by a cone. For appropriate constants describing this interaction the energy barrier can be so high that chirality flipping becomes the principal switching mode. An increase in the electric field can eliminate layer curvature, and therefore the energy barrier, so that switching with molecular rotation on the cone becomes possible. In the present contribution these mechanisms of switching are discussed and the influence of layer curvature on the switching mode is demonstrated.     

2H nuclear magnetic resonance study on the molecular motion in cyanoadamantane. II. Orientationally ordered and glassy crystalline phase

The orientationally ordered crystalline and glassy plastically crystalline phase of cyanoadamantane were investigated using (2)H NMR. Solid-echo line shape, two-dimensional spectrum, and spin-lattice relaxation were analyzed. In both phases, the molecules display solely a rotation around the molecular C(3) symmetry axis. For the orientationally ordered phase, a single correlation time characterizes the motion, and the time constant shows an Arrhenius temperature dependence. In contrast, a broad distribution G[ln(tau)] of correlation times is observed for the glassy plastically crystalline phase that leads to characteristically different NMR features such as "two-phase" spectra and pronounced nonexponential relaxation. The distribution G[ln(tau)] can be derived from a temperature independent distribution of activation energies g(E(a)), with its mean value lying significantly below the activation energy corresponding to the ordered phase. Thus, the molecular uniaxial rotation proves to be a sensitive probe for the energy landscape of the orientationally disordered glassy crystalline phase of cyanoadamantane.     

Modeling anhydrous and aqua copper(II) amino acid complexes: a new molecular mechanics force field parametrization based on quantum chemical studies and experimental crystal data

This paper presents the vacuum structures of aquacopper(II) bis(amino acid) complexes with glycine, sarcosine, N,N-dimethylglycine, and N-tert-butyl-N-methylglycine estimated using the B3LYP method. The differences between the B3LYP vacuum structures and experimental crystal structures suggested considerable influence of crystal lattice packing effects on the changes in the complexes' geometries. A previously developed molecular mechanics force field for modeling anhydrous copper(II) amino acidates was reoptimized to simulate these changes and predict the properties of both trans and cis anhydrous and aqua copper(II) amino acid complexes. The modeling included experimental molecular and crystal structures of 13 anhydrous and 10 aqua copper(II) amino acidates with the same atom types (Cu(II), C, H, N, and O) but various copper(II) coordination polyhedron geometries, crystal symmetries, and intermolecular interactions. The empirical parameters of the selected potential energy functions were optimized on the B3LYP vacuum copper(II) coordination geometries of three anhydrous copper(II) amino acidates and on experimental crystalline internal coordinates and unit cell dimensions of six anhydrous and six aqua copper(II) amino acid complexes. The respective equilibrium structures were calculated in vacuo and in simulated crystalline environment. The efficacy of the final force field, FFW, was examined. The total root-mean-square deviations between the experimental and theoretical crystal values were 0.018 A in the bond lengths, 2.2 degrees in the valence angles, 5.5 degrees in the torsion angles, and 0.395 A in the unit cell lengths. FFW reproduced the unit cell volumes in the range from -8.1 to 9.6%. The means of Cu to axial water oxygen distances were 2.4 +/- 0.1 A (experiment) and 2.6 +/- 0.1 A (FFW). This paper describes the ability of the molecular mechanics model and FFW force field to simulate the flexibility of the metal coordination polyhedron. The new force field proved effective in predicting the most stable molecular conformation of copper(II) amino acidato systems in vacuo.     

Redrawing of oriented polyethylene film

Drawn and subsequently annealed polyethylene film was restretched along the original draw axis at various temperatures. The internal deformation was analyzed in terms of the structural parameters of a simplified model. The elementary deformations are the rotation of crystals around the b axis and shear at the crystal interface. The rigidity of the crystal plays an important role during extension; and as a result, disorientation of chains in the crystal occurs at high strain. At the same time, crystals deform in such a way that the crystalline chains tilt about the b axis along the (h00) plane. This deformation of the crystal is affected by temperature. The increase in long spacing with extension can be interpreted roughly by the changes in structural parameters. The strain in amorphous region in also discussed in relation to these parameters.