Anisotropic Poisson Effect and Deformation‐Induced Fluorescence Change of Elastic 9,10‐Dibromoanthracene Single Crystals

Elastic organic crystals have attracted considerable attention as next‐generation flexible smart materials. However, the detailed information on both molecular packing change and macroscopic mechanical crystal deformations upon applied stress is still insufficient. Herein, we report that fluorescent single crystals of 9,10‐dibromoanthracene are elastically bendable and stretchable, which allows a detailed investigation of the deformation behavior. We clearly observed a Poisson effect for the crystal, where the short axes (b and c‐axes) of the crystal are contracted upon elongation along the long axis (a‐axis). Moreover, we found that the Poisson's ratios along the b‐axis and c‐axis are largely different. Theoretical molecular simulation suggests that the tilting motion of the anthracene may be responsible for the large deformation along the c‐axis. Spatially resolved photoluminescence (PL) measurement of the bent elastic crystals reveals that the PL spectra at the outer (elongated), central (neutral), and inner (contracted) sides are different from each other.     

Preparation of mordenite composite membranes with seeding

Mordenite composite membranes were prepared by means of coating a porous α-alumina support with nanosized mordenite seeds followed by hydrothermal crystallization. A systematic investigation was performed on the influence of several factors such as ageing of the reaction mixture, alkalinity, salt addition and temperature on the formation of a mordenite membrane on the seeded support. The ageing of the reaction mixture reduces the growth rate of mordenite crystal along a-axis and b-axis but hardly influences the growth rate along c-axis. As a result, the boundaries between the surface crystals become a little larger with prolonging the period of ageing time. The growth rate of the mordenite crystal along individual axes increases first and then decreases with increasing concentration of sodium hydroxide. A higher alkalinity is unfavorable for the formation of a continuous mordenite membrane. The addition of salt in the reaction mixture has different effect on the growth rate of the mordenite crystal along each axis. With increasing the amount of salt, there was hardly influence on the growth rate along c-axis, whereas an obvious decline was observed in the growth rate along either a-axis or b-axis, which enlarges the boundaries between the surface crystals. The growth rate of the mordenite crystal increases more along c-axis than that along a-axis or b-axis with increasing temperature for hydrothermal crystallization. The use of a temperature as high as 473 K produces a membrane composed of bar-like crystals with larger boundaries. __________ Translated from Journal of Zhejiang University (Science Edition), 2005, 32(4) (in Chinese)     

Crystal structure,morphology, and phase transitions in aromatic polyimide oligomers. 3. Poly(1,4-phenyleneoxy-1,3-phenylene pyromellitimide)

An aromatic polyimide oligomer, poly(1,4-phenyleneoxy-1,3-phenylene pyromellitimide) (PMDA-3,4'-ODA), was synthesized from pyromellitic dianhydride (PMDA) and 3,4'-oxydianiline (3,4'-ODA) via a melt-polymerization method. This method permits growth of PMDA-3,4'-ODA lamellar crystals and the crystal structure can be studied via electron diffraction (ED) and wide-angle x-ray diffraction (WAXD) experiments. Our structure analysis indicates that this polyimide possesses a two-chain orthorhombic crystal lattice with dimensions of a = 0.848, b = 0.562, and c = 3.365 nm. It has also been found that poly(amic acid) precursors with little imidization possess the same ab lateral lattice packing, but statistical departure from the ordered packing along the c-direction. Upon increasing the degree of imidization through annealing at elevated temperatures, the order along the c-axis was progressively enhanced. Increasing the annealing temperature caused the dimensions of the a- and the b-axes to expand while the crystal correlation lengths decreased laterally. Simultaneously the dimension of the c-axis shrinks with an increase of the crystal correlation length along the chain direction. Crystal morphological study via transmission electron microscopy (TEM) indicates a mainly lamellar crystal texture with different thicknesses depending upon the polymerization conditions. The end lamellar surface is usually smooth. After annealing at elevated temperatures, the lamellar end surfaces become rough, which may be due to chain motion along the c-axis. The annealed PMDA-3,4'-ODA lamellar crystals still show a large amount of defects. © 1994 John Wiley & Sons, Inc.     

Crystal structure of poly(m-phenylene isophthalamide)

The crystal structure of poly(m-phenyulene isophthalamide) was determined by x-ray analysis. The triclinic cell, with a = 5.27 Å, b = 5.25 Å, c (fiber axis) = 11.3 Å, α = 111.5°, β = 111.4° and γ = 88.0° and space group P1, contains one monomeric unit. The crystal density is 1.47 g/cc. The molecules in the crystal are contracted by 1 Å per monomeric unit from the fully extended conformation, and the planes of the benzene rings and adjacent amide groups make angles of about 30°. The crystal is composed of molecular chains connected by N? H···O hydrogen bonds along the a and b axes forming a “jungle gym” network structure. The low tensile modulus of this polymer as compared with that of poly(p-phenylene terephthalamide) is attributed to the contracted molecular conformation.     

An improved model for crystalline orientation of spherulitic polymers

A model is proposed to account for the orientation of crystals in spherulites upon deforming a polymer. The model assumes affine deformation of the spherulite accompanied by three processes of crystal reorientation within the spherulite. These are tilting of molecular chains with respect to the plane of the lamellae, characterized by a parameter K, twisting of the lamallae about the spherulite radii described by η, and rotation of the b crystal axis about the c axis characterized by a third parameter, P. Values of these parameters are fitted to measured orientation functions and compared with experimental measurements of the azimuthal variation of the intensities of the 110 and 200 crystal reflections from low-density polyethylene. Good agreement is found between the experimental and theoretically predicted intensity variation. Time-dependent experiments under relaxational and vibrational conditions are also treated by the theory.     

Crystal orientation and melting behavior of poly(ɛ-Caprolactone) under one-dimensionally “hard” confined microenvironment

Crystal orientation and melting behavior of poly(ε-caprolactone) in a diblock copolymer of poly(ε-caprolactone)-block-poly(2,5-bis[4-methoxyphenyl]oxycarbonyl)styrene) (PCL-b-PMPCS) was investigated. The degrees of polymerization of the PCL and PMPCS block are 200 and 98, respectively. With the PMPCS in a columnar liquid crystalline phase, the diblock is rod-coil one, which exhibits a lamellar phase morphology with the PCL layer thickness of 15.2 nm. Since the glass transition temperature of PMPCS block is much higher than the melting temperature of PCL, the crystallization of PCL is in a one-dimensionally "hard" confinement environment. Mainly on the basis of two-dimensional wide-angle X-ray diffraction experiments, we identified the orientation of PCL isothermally crystallized at various crystallization temperatures (Tcs). At high Tcs (Tc≥10℃), the c-axis of the PCL crystal is along the layer normal of the microphase-separated sturcture. Decreasing Tc can result in the tilting of PCL c-axis with respect to the layer normal. The lower the Tc is, the more the c-axis inclines. Meanwhile, the b-axis of PCL remains perpendicular to the layer normal. At a very low Tc of -78℃, the orientation of the PCL crystals is completely random. For the samples isothermally crystallized at Tc≤10℃, double melting behavior can be observed. While the low temperature endotherm reflects the melting of the crystals originally formed at the Tc applied, the high temperature one is associated with the crystals subjected to the process of recrystallization/reorganization upon heating due to the annealing effect.     

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.     

Die Kristallstruktur des N,N-Dijodformamids HCONJ2

The crystal structure of N,N-Diiodoformamide, HCONI₂, has been determined from three-dimensional diffractometer data and refined to a conventionalR-value of 4.1%. The crystals are orthorhombic, space group Pn 2₁a,Z=4, with the unit cell parametersa=10.758,b=7.075,c=6.671 Å. The molecules are connected by intermolecular I?O-bonds forming chains along thea-axis. Between the chains exist weaker I?O-contacts which link the chains to form layers perpendieular to theb-axis.     

Study of structure and polymerization of epitaxially grown SiPc(OH)2 thin films by high-resolution electron microscopy

Thin films of SiPc(OH)₂ (Pc = phthalocyanine) were formed epitaxially on the (001) surface of mica by vacuum deposition and were then polymerized by heat treatment. The molecular packing of the SiPc(OH)₂ was determined by electron diffraction and high-resolution electron microscopy as triclinic${\rm P\bar 1} $ having dimensions a = 0.727, b = 1.307, c = 0.688 nm, α = 102.5, β = 104.2, and γ = 97.4°. This monomer crystal grows with its c-axis parallel to the a-axis of the substrate mica and its bc-plane parallel to the (001) surface of mica. By heat treatment at 320°C, the SiPc(OH)₂ polymerized with the c-axis of the polymer parallel to the c-axis of the monomer. At 420°C, the c-axis of the polymer became parallel to the a*-axis of the monomer (i.e., perpendicular to the film surface). From high-resolution electron microscopy of partially polymerized specimens, the polymerization was shown to start at the edges of small monomer crystals. This may be considered to be due to the volume expansion during the polymerization. © 1993 John Wiley & Sons, Inc.     

Polymer decoration study in chain folding behavior of solution-grown poly(ethylene oxide) crystals

The polymer decoration method based on the vaporization and condensation-crystallization of polyethylene (PE) upon the fold surface of polymer crystals has been widely used to study the chain folding behavior of the crystals. When this method was utilized to study solution-grown high molecular weight poly (ethylene oxide) (PEO) lamellar crystals, the highly anisotropic, low molecular weight fragment PE decorated become oriented parallel to the fold direction and form rods, which can be observed by transmission electron microscopy (TEM) and electron diffraction (ED). The growth sectors were clearly observed. From the ED patterns the {200} planes of the orthorhombic low molecular weight PE rod crystals can be observed, and the c-axis of these crystals is aligned parallel to the {120} growth planes of the PEO crystals. The decoration results indicate that the major fold orientation of high molecular weight PEO single crystals grown from dilute solution is along the {120} planes. © 1995 John Wiley & Sons, Inc.     

Macroscopic Polarization Change of Mononuclear Valence Tautomeric Cobalt Complexes Through the Use of Enantiopure Ligand

The crystallization of a complex having electron transfer properties in a polar space group can induce the polarization switching of a crystal in a specific direction, which is attractive for the development of sensors, memory devices, and capacitors. Unfortunately, the probability of crystallization in a polar space group is usually low. Noticing that enantiopure compounds crystallize in Sohncke space groups, this paper reports a strategy for the molecular design of non-ferroelectric polarization switching crystals based on the use of intramolecular electron transfer and chirality. In addition, this paper describes the synthesis of a mononuclear valence tautomeric (VT) cobalt complex bearing an enantiopure ligand. The introduction of enantiomer enables the crystallization of the complex in the polar space group (P2₁). The polarization of the crystals along the b-axis direction is not canceled out and the VT transition is accompanied by a change in the macroscopic polarization of the polar crystal. Polarization switching via electron transfer is realized at around room temperature.     

Magnetic structure and properties of Cu3(OH)4SO4 made of triple chains of spins s=1/2

Cu₃(OH)₄SO₄, obtained by hydrothermal synthesis from copper sulfate and soda in aqueous medium, is isostructural with the corresponding antlerite mineral, orthorhombic, space group Pnma (62), with a=8.289(1) b=6.079(1) and c=12.057(1) Å, V=607.5(2) ų, Z=4. Its crystalline structure has been refined from X-ray single crystal and powder neutron diffraction data at room temperature. It consists of copper (II) triple chains, running in the b-axis direction and connected to each other by sulfate groups. The magnetic structure, solved from powder neutron diffraction data at 1.4 K below the transition at 5 K evidenced by susceptibility and specific measurements, reveals that, inside a triple chain, the magnetic moments of the copper ions (μ_B=0.88(5) at 1.4 K) belonging to outer chains are oriented along the c-axis of the nuclear cell, with ferromagnetic order inside a chain and antiferromagnetic order between the two outer chains. No long-range magnetic order is obtained along the central chain with an idle spin behavior.     

Electrochemical/chemical synthesis of highly-oriented single-crystal ZnO nanotube arrays on transparent conductive substrates

Arrays of ZnO nanotube (ZNT) were prepared by a two-step electrochemical/chemical process on a transparent, conductive substrate from an aqueous solution at 85 °C. The as-grown ZNTs are single crystals with wurtzite structure and have good crystalline state. The tubular morphology was formed by the proton generated from anodic splitting of water and defect-selective etching of the electrodeposited ZnO nanorod (ZNR) along the c-axis. The photoluminescence and cathodoluminescence spectra of the ZNT arrays show two emission bands located in the ultraviolet (UV) and visible region, respectively. It was found that the PL intensity in the UV band as well as the ratio of I_uv/I_visible increased with increasing of the excitation intensity.     

Cadmium(II) diallyldithiocarbamato complexes with 2,2′-bipyridine and 1,10-phenanthroline: spectroscopic and crystal structure analysis

Complexes of Cd(II) with diallyldithiocarbamato (hereafter denoted aldtc) and 2,2′-bipyridine (bipy) and 1,10-phenanthroline (phen) are discussed. Derivatives of general formula [Cd(aldtc)₂(NN)] [NN = bipy, 1 and phen, 2] have been obtained by direct reaction between Cd(NO₃)₂ and a 2 : 1 molar ratio of aldtc and NN. The new complexes have been characterized by IR, ¹H, and ¹³C NMR spectroscopy. Their single crystal structures were also determined. Compounds 1 and 2 have severely distorted octahedral coordination around cadmium, defined by an N₂S₄ donor set. The structure of 1 is isomorphous with the recently reported zinc analogue. The crystal packing of 1 shows different non-classical intermolecular interactions represented in both hydrophilic (π)C–H ··· S and hydrophobic (allyl)C–H ··· C(π) intermolecular interactions. Such interactions result in a chain arrangement of molecules along the crystallographic c-axis. These chains are further connected via π ··· π stacking along with (π)C–H ··· S parallel to b leading to an overall crystal packing that can be regarded as layers of complexes along the bc plane. Molecules in the crystal structure of 2 are arranged into infinite chains, down the b-axis, that are connected by aryl ··· aryl stacking. The chains are further connected to each other in a and c directions via (allyl)C–H ··· S interactions.     

Novel tetrapodal molecules and reticular polyamides based on tetraphenylmethane

A series of tetrapodal derivatives of tetraphenylmethane were synthesized and characterized. Crystals obtained from tetrakis(4-acetamidophenyl)methane (1c) and from tetrakis[4-(4-aminobenzamido)phenyl]methane (2b) were analyzed by X-ray diffraction. The analyses pointed to the crystal packing problems faced by molecules of this kind by showing that the crystals, with composition1c·2DMF·2H₂O and2b·2DMSO, respectively, contained cocrystallized solvent molecules. The solvent molecules were found in both cases to be held in place by H bonds; in the case of2b·2DMSO they occupied channels running along theb axis. Tetrakis(4-aminophenyl)methane (1b) was used in polycondensation reactions with terephthalic acid, under modified Yamazaki conditions, to produce rigid aromatic polyamide networks. The networks were obtained as gels encompassing the whole volume of the reaction mixture. The volume of the gels did not vary noticeably upon changing the solvent (1-methyl-2-pyrrolidone) with less polar solvents, but the gels collapsed upon drying. No crystallinity was observed.     

Morphological and structural features of heat-treated drawn polypropylene/high-density polyethylene blends

The ion etching technique has been applied to a morphological study of mechanically blended polypropylene (PP) with high-density polyethylene (HDPE). Samples blended to PP/HDPE compositions of 65/35 and 85/15 by weight were highly drawn and then heat treated for 30 min at selected temperatures up to 163°C. When these samples are carefully ion-etched several features are observed in electron micrographs, namely (i) crosshatched, and (ii) twisted or layered textured inclusions of HDPE crystals within arrays of lamellalike PP crystals situated perpendicular to the direction of drawing. X-ray diffraction measurements of the drawn samples heat treated in the range 145–163°C for 30 min shows that oriented HDPE crystallizes with b-axis orientation along the drawing direction. Supporting evidence is obtained from electron diffraction measurements. The molecular weight of the HDPE component is a major factor in the b-axis-oriented growth of HDPE crystals in PP/HDPE blends.     

Crystal orientation in a semicrystalline polymer in relation to deformation of polymer spherulites. II. Orientation distribution function of crystallites within crystal lamella as a function of lamellar orientation

A model relating crystal orientation in a semicrystalline polymer to the deformation of polymer spherulites is proposed. The distribution function for orientation of crystallites within crystal lamellae is assumed to be a function of lamellar orientation. In addition to the orientation of crystal lamellae in affine fashion, several parameters are introduced to characterize the untwisting of the crystal lamellae and the four different types of orientations of the crystallites within the crystal lamellae in the undeformed and deformed states of the spherulite. The model was tested by experiments in uniaxial stretching of a low-density polyethylene. The theoretical distributions of orientation of given reciprocal lattice vectors of the crystallites, such as the reciprocal lattice vectors of the (110) and (200) crystal planes, are compared with the results of x-ray diffraction experiments. It was found that the most important factors in fitting the model to experimental results are: (a) the fraction of crystallites having random orientation within lamella and, in turn, representing the degree of imperfection of the lamella in the undeformed state; (b) the ease of transition of crystal orientation within lamella from b-axis orientation parallel to the lamellar axis to two types of c-axis orientations (type C_a and type C_r) parallel to the stretching direction; and (c) the fraction of crystallites having orientation in type C_r (unfolding mechanism) rather than type C_a (rotation mechanism).     

An x-ray pole figure analysis on biaxially deformed polyethylene film

The orientational states induced upon two-step biaxially stretching low-density polyethylene at 25°C have been investigated. A pole figure analysis of the (200), (020), and (002) crystalline planes has been employed to elucidate the evolution of the molecular crystalline orientation as a function of biaxial stretching. The initial uniaxial-like orientation induced along the extrusion direction of the films was gradually lost upon transverse stretching and, consequently, replaced by a biaxial orientation as suggested by the orientation functions. In these cases, the a crystallographic axis was observed to be strongly oriented along the film normal, thus confining the c and b axes to the film plane. The pole figures clearly indicate that the c and b axes are preferentially aligned 45° with respect to the stretching directions. This unique orientational state of the orthorhombic unit cell of polyethylene has been termed a biaxial-double orientation. Birefringence measurements on the biaxial samples indicated that the amorphous and crystalline regions are simultaneously biaxially oriented. The evolution of the crystalline orientation as a function of stretching was conveniently followed on a White/Spruiell orientation triangle. Quantification was hindered, however, by the presence of different crystal populations in the biaxially stretched samples. © 1994 John Wiley & Sons, Inc.     

Micropatterning of semicrystalline poly(vinylidene fluoride) (PVDF) solutions

Micropatterning of a semicrystalline poly(vinylidene fluoride) (PVDF) solution was performed by a temperature controlled capillary micromolding where the rate of solvent evaporation was controlled by substrate temperature. In order to choose proper solvents for micropatterning, we have investigated the solubility of PVDF in various organic solvents and crystal structures of the PVDF bulk films cast from the solvents. The films prepared from the polar solvents such as dimethylformamide (DMF), dimethyl sulfoxide (DMSO) dominantly showed γ type crystals regardless of preparation temperature, while the films from tetrahydrofuran (THF) exhibit α type crystals and the ones from acetone and methyl ethyl ketone (MEK) show the characteristics of both α- and γ-PVDF. The quality of micropatterns and shapes of the PVDF crystals in the patterns significantly depend on solvent evaporation rates. Micropatterns of PVDF formed in DMF at 120 °C showed the best uniformity in shape. Crystals of the PVDF nucleated at the center regions of microchannels tended to be elongated with the b-axis of γ-PVDF crystals along the channels as the concentration of the solution decreased. In contrast, crystals nucleated at the corner regions of the channels had their b-axis oriented perpendicular to the channels. In line patterns with the width of 2 μm, the corner nucleated crystals were dominant and a resulting bamboo-like crystalline microstructure was observed in which the b-axis of γ-PVDF crystals, fast growth direction, is oriented normal to the microchannels. The crystal structures of the bulk films and the micropatterns were characterized by X-ray diffractometer, Fourier transform infrared spectroscope in Attenuated Total Reflection mode, Polarized Optical and Scanning Electron Microscope.     

Adsorption characteristics of synthesized mordenite membranes

Nitrogen adsorption at 77 K was measured for a self-supporting mordenite membrane synthesized on and detached from, a polytetrafluoroethylene (PTFE) substrate, and for a simultaneously formed powder. The adsorption by the membrane saturated an amount which was about half that found for adsorption by the powder. To examine this difference in adsorption characteristics, both of powder and membrane were measured for adsorption for water, methanol,n-hexane andtert-butyl alcohol. For methanol,n-hexane andtert-butyl alcohol, the powder and membrane both showed the same adsorption behavior as for nitrogen. When water molecules were adsorbed, however, there was no difference in saturated adsorption amount between powder and membrane, suggesting the presence of deformed pores in the rectangular crystal layer of the mordenite membrane. The deformed pores are assumed to occur as gaps among crystallites which displaced along theab planes of the rectangular crystals, forming the rectangular crystal layer. The channel bonding sites resulting from such displacement were found to serve as pore walls against adsorbable molecules which have a cross-sectional area greater than that of the water molecule. and so to hinder their entrance into the deformed pores. X-ray diffraction analysis revealed that the rectangular crystals have no periodic, continuous structure along thec-axis; they show a slight distortion of the crystallite shift from the plane perpendicular to thec-axis.