Modes of deformation under varied tensile directions in laminar,colloidal gold

In perfect crystals of laminar colloidal gold, free from dislocations and stacking faults, the modes of deformation have been studied systematically, as a function of resolved shear stress or normal stress for each mode, using electron microscope and diffraction. The main modes of plastic deformation are cleavage crack, single glide and mechanical twinning. The cleavage crack is normally found under the tensile direction which gives the maximum normal stress to the cleavage surface. There is, however, another case of cleavage crack caused as a result of the glide deformation non-parallel to the crystal surface. This is the mode of cleavage characteristic of thin crystals. The single glide along the direction parallel to the surface, and the mechanical twinning obey to the resolved shear stress criterion. The latter is in contrast with the mechanical twinning in bulk crystals where in general the criterion does not hold. The twinning shear demonstrated at the edge of the crystal is much larger than that estimated. High resolution lattice images reveal the consecutive occurrence of twinning and detwinning or simple glide in atomic scale. This is another example exclusively found in thin crystals.     

Orientation of crystallites in lightly crosslinked isotactic polypropylene crystallized from the melt under uniaxial compression

A lightly crosslinked polymer film was made from isotactic polypropylene by gammaray irradiation in an acetylene atmosphere. When the crosslinked polymer film was crystallized from the melt under uniaxial compression, a unique alignment of crystallites is found. The (040) crystal plane is preferentially oriented parallel to the film surface at relatively low degrees of compression, and the (110) and (130) crystal planes are oriented parallel to the film surface at higher degrees of compression. The origin of these orientations, analogous to that previously found in a lightly crosslinked polyethylene, is discussed.     

INFLUENCE OF ELECTRIC FIELDS ON FLUORESCENCE QUENCHING OF CHLOROPHYLL a IN NEMATIC LIQUID CRYSTAL MATRIX

Abstract— An electric field enhances the yield of fluorescence of chlorophyll in a liquid crystal solvent. The presented data suggest that the electric field effect is caused by the decrease in the efficiency of fluorescence quenching by ions. Quenching of each polarized component of fluorescence of chlorophyll molecules oriented by the liquid crystal matrix is different. The relative increase in fluorescence yield due to the applied electric field is stronger for a fluorescence component polarized parallel to the direction of liquid crystal orientation than for the perpendicular component.     

Epitaxial crystallization of homopolymers on single crystals of alkali halides

Epitaxial deposition of homopolymers from solution [polyethylene, isotactic polystyrene, poly-3,3-bischloromethyloxacyclobutane (Penton) and polypropylene] was found on the (001) faces of cleaved alkali halide single crystals. Electron and optical microscopy studies have shown that the polymer usually grew from small, rodlike crystallites which were oriented in (110) directions of the halide crystal. Large oriented, four-leaved, “rose” structures also were observed for polyethylene. Electron diffraction studies indicate that the polymer chain axes for polyethylene, isotactic polystyrene, and Penton generally lie parallel to the (001) faces of the halide crystal and are also oriented in the 〈110〉 directions of the crystal face. Investigations on the effect of various halide substrates upon the epitaxial crystallization habit of polyethylene inferes that lattice matching does not play the major role in orientation. Two possible explanations are offered for this epitaxial behavior.     

Confined crystallization of cylindrical diblock copolymers studied by dynamic Monte Carlo simulations

We report dynamic Monte Carlo simulations of polymer crystallization confined in the cylindrical microdomains of diblock copolymers. The microdomains were prepared via spontaneous microphase separation from homogeneous melt, and the major component was then frozen in a vitreous amorphous state to make a hard confinement to the crystallization of the minor component. We found that during the isothermal crystallization at high temperatures, crystal orientations are dominantly perpendicular to the cylinder axis at the early stage of crystal nucleation and remain to the final state; while if the block junctions are broken before crystallization, crystal orientations are dominantly parallel at the early stage of crystal nucleation, and eventually other orientations take the place of parallel preferences. Analysis of bond orientations in the heterogeneous melts demonstrates the microscopic origin of oriented crystal nucleation.     

Poly(p-benzamide): Magnetic field orientation,solvation, and crystal–crystal transformations

The morphological features of poly(p-benzamide) films cast in a magnetic field from solutions in N,N-dimethylacetamide containing LiCl are reported. Three crystal modifications are found, one solvated and the other two containing no solvent. The solvated crystal grown in a magnetic field is oriented with the molecules parallel to the field. It transforms to an oriented amorphous phase by loss of solvent, and this conversion is accelerated by the presence of moisture. Upon annealing at an elevated temperature, the crystalline solvate transforms to a second crystal form, while the amorphous sample is converted to a third crystalline modification. All three crystalline forms have almost the same fiber identity period, which corresponds to a nearly fully extended chain conformation.     

General analysis of the measurements of the lateral crystal lattice moduli of semicrystalline polymers by x-ray diffraction and the application to nylon 6

A mathematical representation based on a linear elastic theory is proposed by which one may investigate the dependences of molecular orientation and crystallinity on the crystal lattice moduli and linear thermal expansion coefficients in the direction perpendicular to the chain axis as commonly measured by x-ray diffraction. In the theoretical calculation, a previously introduced model was employed in which oriented crystalline phase is surrounded by oriented amorphous phase and the strains of the two phases at the boundary are identical. The mathematical analysis indicated that the lateral crystal lattice moduli and linear thermal coefficients as measured by x-ray diffraction may be different from the intrinsic crystal moduli and linear thermal coefficients of a crystal unit cell, depending on the structure of the polymer solid. The numerical calculation was applied to nylon 6. As a result, it may be confirmed that the lateral crystal lattice moduli measured by x-ray diffraction are sensitive to the morphology of the bulk speciments and close to the intrinsic crystal moduli if the morphology of the test specimen can be represented by a parallel model with respect to the original stretching longitudinal direction.     

Polarization of the monomer and excimer fluorescence of pyrene derivatives in liquid-crystalline hosts

The monomer and excimer fluorescence polarization of 4,9-disubstituted pyrenes with molecular long axes nearly perpendicu- lar to the pyrene skeleton were measured in a nematic liquid crystal. By comparison with unsubstituted pyrene it is found that the excimer transition moment is oriented parallel to the sandwich plane and perpendicular to the pyrene long axis.     

Highly oriented structure formed in a lamella-forming diblock copolymer with high molar mass

Highly oriented films were prepared simply by annealing a lamella-forming block copolymer, poly(ethylene oxide-b-styrene) (PEO-b-PS), with high molar mass under a pressure of 0.2 MPa. The oriented structures were characterized by small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD). The SAXS measurements showed that the lamellar layers of the block copolymer are highly oriented parallel in the film plane. The WAXD images showed that the c-axis of PEO crystals was oriented normal to the film plane. The Hermans-Stein orientation functions for the lamellar layer and the crystal axis are 0.954 and −0.466, respectively, and are close to the values of perfect orientation. It was considered that the highly oriented structure was formed by the combined effects of shear flow and self-organization of the block copolymer during annealing under stress. The high degree of orientation both for the lamellar layer and crystal planes also suggested that the crystallization in the confined domains results in a high degree of orientation of PEO crystals with respect to the lamellar interface of the block copolymer.     

含少量共聚组分聚乙烯熔体拉伸薄膜的形态结构

利用透射电子显微学(TEM)和示差扫描量热学(DSC)等方法研究了含少量丁烯-1组分(摩尔分数为0.64%)的聚乙烯共聚物(PE100)熔体拉伸高取向薄膜的形态结构. 结果表明, 在PE100熔体拉伸薄膜中, 除存在高取向片晶结构外, 还含有大量的纤维晶, 纤维晶平行于拉伸方向, 穿过几个片晶区, 平均直径约为12 nm. 模拟实验结果表明, 纤维晶的生成源于聚乙烯共聚物中的超高分子量组分, 但不同于传统意义上的伸直链纤维晶, 其形态特征应为晶桥结构. 由此提出了晶桥结构纤维晶模型, 该模型不但有助于深入理解和认识聚合物取向结晶机理, 同时也为该材料的高性能化提供了理论依据.     

1‐[2‐(1‐Hydroxy­cyclo­hexyl)‐2‐(4‐methoxy­phenyl)­ethyl]­di­methyl­ammon­ium chloride (venlafaxine hydro­chloride)

The crystal structure of racemic Venlafaxine hydro­chloride, C₁₇H₂₈NO₂⁺·Cl^?, consists of two types of parallel chains formed by translated Venlafaxine⁺ cations, hydrogen bonded by Cl^? anions, and characterized by the opposite chirality of their constituent mol­ecules. These chains organize in two different types of broad layers of opposite handedness, related by a glide plane.     

Amperometric detection of DNA hybridization on a gold surface depends on the orientation of oligonucleotide chains

We tested the possibility of amperometric detection of DNA hybridization on a gold surface influenced by the immobilization of oligonucleotide giving different orientations of single stranded DNA relative to the gold surface. The DNA sensor was fabricated by chemisorption of 18-mer oligonucleotide modified by a phosphorothioate group either at its 3' or both 3' and 5' terminal. After immobilization of oligonucleotide to the gold support, the sensor was immersed in 11-mercaptoundecanoic acid (MUA) solution. Further chemisorption of MUA resulted in approximately 10-fold increase of resistance of the organic layer. Addition of complementary oligonucleotide resulted in an increase of conductivity for DNA sensor oriented perpendicular to the gold support (DNA with one thiol group), while the conductance decreased for DNA sensor with single stranded DNA oriented parallel to the gold support (with DNA modified by thiol groups at both 3' and 5' terminals). Addition of non-complementary chain resulted a slight decrease or no change of sensor conductivity. The hybridization process at both types of DNA orientations is not cooperative and can be described by Langmuir isotherms. The hybridization event on gold support has been confirmed by mass detection using the quartz crystal microbalance technique.     

Oriented crystallization of poly(L‐lactic acid) in uniaxially oriented blends with poly(vinylidene fluoride)

This article describes the oriented crystallization of poly(L ‐lactic acid) (PLLA) in uniaxially oriented blends with poly(vinylidene fluoride) (PVDF). Uniaxially drawn films of PLLA/PVDF blend with fixed ends were heat‐treated in two ways to crystallize PLLA in oriented blend films. The crystal orientation of PLLA depended upon the heat‐treatment process. The crystal c‐axis of the α form crystal of PLLA was highly oriented in the drawing direction in a sample cold‐crystallized at T_c = 120 °C, whereas the tilt‐orientation of the [200]/ [110] axes of PLLA was induced in the sample crystallized at T_c = 120 °C after preheating at T_p = 164.5–168.5 °C. Detailed analysis of the wide‐angle X‐ray diffraction (WAXD) indicated that the [020]/ [310] crystal axes were oriented parallel to the drawing direction, which causes the tilt‐orientation of the [200]/ [110] axes and other crystal axes. Scanning electron microscopy (SEM) suggested that oriented crystallization occurs in the stretched domains of PLLA with diameters of 0.5–2.0 μm in the uniaxially drawn films of PVDF/PLLA = 90/10 blend. Although the mechanism for the oriented crystallization of PLLA was not clear, a possibility was heteroepitaxy of the [200]/[110] axes of the α form crystal of PLLA along the [201]/[111] axes of the β form crystal of PVDF that is induced by lattice matching of d₁₀₀(PLLA) ≈ 5d₂₀₁(PVDF). © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1376–1389, 2008     

A study of the acoustic mode structure of oriented poly(ethylene)

The low-frequency acoustic vibrational modes of solid poly(ethylene) (PE) oriented by stretching and hydrostatic extrusion are studied with Brillouin spectroscopy. The experimental results evidence a damping of the longitudinal acoustic mode propagating in the direction parallel to the orientation axis of the samples. The results are discussed in terms of the theoretically derived acoustic dispersion relations for the PE crystal.     

Morphology and Crystal Structure of Wholly Aromatic All-Para Polyamide-Hydrazide Polymers

The morphology of some amide-hydrazide polymers of the type useful for high-modulus X-500 class fibers has been characterized by transmission electron microscopy of thin films crystallized from dilute solution. Selected area electron diffraction was used to characterize the crystallinity and crystal structure of the thin films and precipitated polymer. The films were cast from concentrated solutions and crystallized by heating the films. The results of these studies revealed several unique features relative to the crystal structure of the all-para polymers. Thin films of the crystallized polymer showed a distinctive crystalline texture—the molecular chains were found to be preferentially oriented parallel to the film plane and randomly oriented about an axis normal to the film plane. Electron diffraction measurements showed equatorial reflection maxima at tilt angles of = 30, ±48, and =59 when the films were tilted on an axis parallel to the film plane. From these results a tentative crystal unit cell and theoretical crystal density were determined: a = 8.5 [Agrave], b = 4.9 Å, c (chain axis) = 29.6 Å, p (density) =1.51 g/cc. The value a/b = 1.735, which is very near 3¹/², implies essentially hexagonal packing of the chains. Crystallization from dilute solution revealed lamellar structures resembling “single crystals” in the electron microscope similar to those observed in other crystalline polymers. However, in contrast to these other polymers, these “crystals” are not likely to contain folded chains because of the very rigid nature of the all-para poiyamide-hydrazide.     

Effect of magnesium ions on oriented growth of calcite on carboxylic acid functionalized self-assembled monolayer

The combined effect of templating and solution additives on calcite crystallization was studied. Self-assembled monolayers of mercaptoundecanoic acid supported on silver, as templates, induced the uniform, oriented nucleation of calcite from the (012) plane. The presence of Mg2+ in the crystallizing solution affected the crystal growth dramatically, due to the selective Mg binding to the calcite planes roughly parallel to the c-axis. Highly homogeneous arrays of oriented crystals with characteristic sizes, shapes, and morphology, depending on the relative concentration of Mg and Ca ions, were synthesized.     

Theoretical insight into the disordered structure of (Z)‐2‐[(E)‐(4‐methoxybenzylidene)hydrazinylidene]‐1,2‐diphenylethanone: the role of noncovalent interactions

A global glide disorder has been discovered during an X‐ray investigation of the crystal structure of (Z)‐2‐[(E)‐(4‐methoxybenzylidene)hydrazinylidene]‐1,2‐diphenylethanone ( MHDE , C₂₂H₁₈N₂O₂) at room temperature. In another crystal, however, such disorder disappears (still at room temperature). Even though the disorder may be partly due to the poor quality of the harvested crystal, the structure can shed light on the nature of disorder. With the help of quantum chemical calculations, it is found that the global disorder seems to be connected with the need for stabilization of the somewhat rigid but mobile and unstable molecular structure. The most relevant feature driving the packing of the disordered structure concerns the slight perturbations (such as glide) of two or more disorder components (fractional occupancies) distributed throughout the crystal.     

Quiescent and strain-induced crystallization of poly(p-phenylene terephthalamide) from sulfuric acid solution

Quiescent and strain-induced crystallization of poly(p-phenylene terephthalamide) (PPTA) from sulfuric acid solution has been studied. Negative spherulites (SA-PPTA spherulites) are formed from hot concentrated solutions by cooling. The spherulite consists of radiating fibrous lamellae several hundred angstroms wide. The electron diffraction pattern indicates that PPTA molecules are oriented perpendicular to the long axes of the fibrous lamellae and that the [010] or [110] direction of the modification I crystal and [010] direction of the modification II crystal are parallel to the long axes of the fibrous lamellae. The width of the lamellae is much smaller than the chain length of the starting PPTA. It appears that hydrolysis of PPTA during melting crystallization determines the chain length, i.e., the width of the fibrous lamella. Stacked, lamellar structures like “row structures” are formed under shear. The longer axes of the fibrous lamellae are oriented perpendicular to the shear direction. It is confirmed by electron diffraction studies that the PPTA molecules are oriented parallel to the shear direction. Well-developed fibrils with the PPTA molecules oriented to the fibril axis, are formed by adding the SA-PPTA spherulites to water with vigorous stirring.     

原位磁场下粉末样品的X射线衍射图谱

To obtain more crystal and magnetic structural information of powder crystals,magnetic field is introduced into X'Pert-MPD XRD apparatus with the strength of 0. 42 T and two different directions:one direction of magnetic field is vertical to the sample holder and another is parallel. XRD patterns in situ magnetic field are obtained for six samples which are representative of paramagnetic,diamagnetic,ferromagnetic,ferrimagnetic,antiferromagnetic substances and reduction product of FeCl2 by NaBH4 respectively. Compared with XRD patterns obtained in the zero magnetic field,there are some diffraction peaks disappear,some occur,or some diffraction angles and counts change. In addition,the patterns are different under the different direction of magnetic field. The cause is that magnetic dipoles in crystals are oriented along with the direction of magnetic field. The oriented magnetic dipoles produce stress in crystals and make crystal lattice changed（such as magnetostriction）or even turn particles aligned along with the direction of magnetic field to form preferred orientation of particles.     

MFI型沸石晶体的择优定向生长

首次采用"双模板剂"法在SiO2-Na2O-正丙胺-溴化N-乙基-六亚甲基四胺(EtHMTA^+)-NaF-H2O体系中合成得到了b轴择优取向的ZSM-5(MFI型)晶体,并用扫描电镜(SEM)和XRD进行表征。择优取向程度与所用的两种模板剂的比例有关,当正丙胺:EtHMTA^+比为0.7:0.3时,ZSM-5晶体择优取向最明显。