Lattice imaging of radiation-sensitive polymer crystals

The total end-point dose (i.e., the electron irradiation dose necessary for complete destruction of the crystal lattice) was measured at 120 kV and room temperature for poly(ethylene oxide), polyethylene, isotactic polystyrene (i-PS), poly(p-xylylene), ramie and bacterial cellulose, and lobster chitin. On the basis of the results obtained, the possibility of lattice imaging of polymer crystals is discussed. As reported in an earlier preliminary paper, 1.1- and 0.55-nm lattice fringes were resolved in i-PS single crystals by using a conventional transmission electron microscope equipped with a device for low-dose imaging. In this paper, the detailed procedure for lattice imaging of i-PS crystals is described and various features of the lattice images are discussed.     

Dynamic imaging of enzymatic events at polyelectrolyte-disrupted phospholipid membranes using liquid crystals

In this study, we employed a simple liquid crystal (LC)-based system to dynamically image enzymatic events at the aqueous/LC interface decorated with polyelectrolyte-disrupted phospholipid membranes. Since polyelectrolytes were shown to disrupt the arrangement of the self-assembled phospholipid monolayer and induced a dark-to-bright shift in the optical response of LCs that support the phospholipid membrane, we observed that the transfer of an aqueous solution of protease onto the polyelectrolyte-disrupted phospholipid membrane resulted in a gradual recovery of the optical response of LCs from bright to dark appearance. Due to the enzymatic event that occurs at the aqueous/LC interface, the generated polyelectrolyte fragments desorbed from the interface to the bulk solution. This led to the restoration of the disrupted phospholipid monolayer, which resulted in recovery of the optical response. These results suggest that the polyelectrolyte-decorated membrane-supported LCs could be potentially used to examine a range of biological interactions that involve polyelectrolytes. Furthermore, the LC-based system holds great promise for label-free and real-time investigation and detection of biomolecular interactions coupled to membrane disruption and restoration, which might have potential utility in the clinical diagnosis and treatment of membrane-associated disease.     

Photocatalytic oxidation surfaces on anatase TiO2 crystals revealed by single-particle chemiluminescence imaging

We report a single-particle approach for studying the photocatalytic oxidation reaction on individual anatase TiO(2) particles. Single-particle kinetic and imaging analyses of the chemiluminescence (CL) emitted from the probe dye molecules revealed that the oxidation reactivity is not significantly dependent on the crystal faces.     

Self-alignment of dye molecules in micelles and lamellae for three-dimensional imaging of lyotropic liquid crystals

We report alignment of anisotropic amphiphilic dye molecules within oblate and prolate anisotropic micelles and lamellae, the basic building blocks of surfactant-based lyotropic liquid crystals. Absorption and fluorescence transition dipole moments of these dye molecules orient either parallel or orthogonal to the liquid crystal director. This alignment enables three-dimensional visualization of director structures and defects in different lyotropic mesophases by means of fluorescence confocal polarizing microscopy and two-photon excitation fluorescence polarizing microscopy. The studied structures include nematic tactoids, Schlieren texture with disclinations in the calamitic nematic phase, oily streaks in the lamellar phase, developable domains in the columnar hexagonal phase, and various types of line defects in the discotic cholesteric phase. Orientational three-dimensional imaging of structures in the lyotropic cholesterics reveals large Burgers vector dislocations in cholesteric layering with singular disclinations in the dislocation cores that are not common for their thermotropic counterparts.     

Circular dichroism imaging microscopy: application to enantiomorphous twinning in biaxial crystals of 1,8-dihydroxyanthraquinone

A microscope was constructed for imaging circular dichroism of heterogeneous anisotropic media. To avoid linear biases that are common with electronic circular polarization modulation, we chose a retrogressive solution: mechanical light modulation by rotating a linear polarizer with respect to a quarter wave plate continuously tuned by tilting to the operating wavelength. Our comparatively slow technique succeeds with near-perfect circular input and signal averaging using a CCD camera. We have applied the method to anomalously birefringent crystals of 1,8-dihydroxyanthraquinone that are shown to have intergrown mirror image domains, undetected by X-ray diffraction because the twinning complexity renders differences in anomalous dispersion, already small, unreliable. The origin of the anomalous birefringence and the assignment of the absolute configuration are discussed.     

Orientation of mineral crystals by collagen fibers during in vivo bone engineering: An X-ray diffraction imaging study

The mechanism of mineralized bone matrix deposition was investigated taking advantage of a tissue engineering approach in which bone tissue is formed when porous ceramic scaffold is loaded with bone marrow stromal cells and implanted in vivo. The aim of our study is to point out the interaction between the newly formed mineral crystals and the scaffold imposing the three-dimensional desired architecture to the growing bone. High spatial resolution Small Angle X-ray Scattering measurements obtained using synchrotron radiation and X-ray waveguide as optical element allowed a local structural study at the bone–scaffold interface. Using an original methodology for data analysis, we obtained a two-dimensional microscopic map of the mineralization degree, the collagen presence and the mineral orientation degree around the scaffold pore.     

The equilibrium shapes of crystals and of cavities in crystals

Surface free energies are assumed to be the sum of the excess free energies of bonding of molecules in or near the surface, and the stable form of a crystal or cavity is assumed to be the form that makes the sum of these excess free energies a minimum. When only plane surfaces are allowed, this model predicts the same shapes for crystals as an equation of Wulff (2. Kristallogr. 34, 449 (1901)), which is based on the macroscopic thermodynamic relation of Gibbs (“The Collected Works, Vol. 1.: Thermodynamics,” Longmans, Green, New York (1931)). The model predicts rounding of edges and corners of kinds which are not allowed by the Wulff relation and predicts that spherical forms of particles and cavities can be stable despite anisotropic surface free energies. The model provides a useful framework for analysis of whether unstable crystal or cavity shapes will evolve into stable or metastable forms. Some crystals and cavities that have been assumed to have equilibrium shapes instead have metastable shapes.     

Extended-chain crystals

Summary The morphology of extended chain lamellae and fibrous polytetrafluoroethylene has been analyzed by electron microscopy and compared to polyethylene. The crystal growth mechanism of initial folding on molecular nucleation followed by chain extension is applicable to both polymers and seems to be a general mechanism for crystallization of prepolymerized linear macromolecules. Differences arise from the branching mechanism of the spherulites. Annealing the striated surface created on fracture could be shown to lead to folded chain ripples of time and temperature dependent thickness. Fibrous crystals of smooth and shish-kebob-type appearance were grown from gaseous tetrafluoroethylene.

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Zusammenfassung Die Morphologie der extended chain-Lamellen und von faserigem Polytetrafluoräthylen wird elektronenmikroskopisch analysiert und mit Polyäthylen verglichen. Der Kristallwachstumsmechanismus anfänglicher Faltung bei molekularer Nukleation, gefolgt von Streckung der Ketten, kann auf beide Polymere angewendet werden und scheint ein allgemeiner Mechanismus der Kristallisation von polymerisierten linearen Makromolekülen zu sein. Unterschiede entstehen vom Verzweigungsmechanismus bei den Sphärolithen. Tempern der gestreiften Bruchflächen — so ließ sich zeigen-führt zu Riffeln von gefalteten Ketten mit zeit- und temperaturabhängigen Dicken. Faserige Kristalle vom glatten und vom Schaschlik-Typ wachsen von gasförmigem Polytetrafluoräthylen.

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For part I–VI of this series see J. Polymer Sci., Part A2, 2043–2113 (1969), Part VII, J. Polymer Sci., Part B,10, 57 (1972).

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Dedicated to ProfessorR. Hosemann on the occasion of his 60th birthday.     

Morphology of polypropylene crystals. II. Twinning of lamellar crystals

Twinned crystals were obtained from fractionated isotactic polypropylene of M?_w = 600,000 by isothermal crystallization at 130°C. for 20 hr. from dilute α-chloronaphthalene solution (0.005 wt.-%). Electron microscopic observations confirm that the molecular chains of polypropylene lamellar crystals extend along the [100] direction while the folding itself occurs within the (010) planes in the monoclinic crystal form. On this basis it is shown that polypropylene forms twinned crystals in which the composition plane is the (1k0) planes. It can be deduced that the formation of twin nucleus occurs before twinning, and then growth occurs from the neighboring region of the crystal boundary by chain folding along the [100] direction.     

Development of a new software for the X-ray structural analysis of polymer crystals by utilizing the X-ray imaging plate system

A software and some useful tools have been developed for identifying individual x-ray reflectional peaks recorded with an x-ray imaging plate system. These techniques were applied to analyze the crystal structure of uniaxially oriented polymer samples. Characteristic features of the present method may be summarized as follows. (1) The indexing of the observed reflections and the determination of the unit cell parameters can be made easily on the display of the computer. (2) The integrated intensity of the individual component of the overlapped reflections can be evaluated quantitatively through the curve separation technique. The R_merge's for the equivalent reflections were 5–6%, indicating the exact evaluation of the integrated intensities. (3) The thus obtained reflectional data were successfully utilized for the extraction of the initial structural models by the direct method. The actual applications have been made for orthorhombic polyethylene, trigonal polyoxymethylene, and isotactic polybutene-1, giving the refined crystal structures including even the positions of hydrogen atoms in some cases. The reliability factors were 12, 5, and 15%, respectively, for these three polymer cyrstals. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1677–1700, 1997     

From colloids in liquid crystals to colloidal liquid crystals

ABSTRACT

Liquid crystals in combination with nanoparticles are a fascinating topic of research, because of the wealth of aspects and questions to study. These range from simple effects of nanoparticles on phase transitions and phase diagrams, to the tuning of physical properties, adding of novel functionalities, all the way to the formation of spontaneous order by nanoparticles themselves and the possibilities that templating has for future materials design and applications. This article intends to provide a flavour of the multiplicity, variety and diversity that these thermotropic and lyotropic systems have to offer in the area of materials development, which we believe will become increasingly important, especially for switchable non-display applications and nanotechnology. It is not intended to provide a conclusive overview, which would be a presumptuous attempt considering the limited space available, but rather to place our own work into a wider context and to point out some more recent developments and trends in liquid crystal – nanoparticle dispersions.     

Morphology of polypropylene crystals. I. Dilute solution-grown lamellar crystals

The dependence of crystalline morphology of isotactic polypropylene crystallized from dilute solutions on its molecular weight and growing conditions and the mechanism of crystal growth were studied by electron microscopy and electron diffraction. Lathshaped lamellar crystals 150–300 A. in thickness are obtained from fractionated polypropylene powders of M _w (average molecular weight) = 600,000 and 240,000, but not from the samples of M _w = 82,000 and 44,000, by means of isothermal crystallization at 130°C. for 20 hr. in dilute α-chloronaphthalene solution (0.005 wt.-%). Precipitation of the fractionated polypropylene sample of M _w = 82,000 from a dilute solution of carbitol gives typical dendritic crystals under the same isothermal crystallizing conditions as mentioned above. The mode of chain folding in these crystals based on the orientation and the crystal structure of the lamellar crystals agrees with that proposed by Sauer, Morrow, and Richardson. From the morphological observations, the mechanism of growth pertinent to polypropylene lamellar crystals is presumed to be as follows: fibrils at first aggregate, then the molecular chains are folded to form small lamellae, and then these small lamellae accumulate compactly to grow to large, lath-shaped, lamellar crystals.     

Multicomponent crystals of erlotinib

Erlotinib [systematic name: N‐(3‐ethynylphenyl)‐6,7‐bis(2‐methoxyethoxy)quinazolin‐4‐amine], a small‐molecule epidermal growth factor receptor inhibitor, useful for the treatment of non‐small‐cell lung cancer, has been crystallized as erlotinib monohydrate, C₂₂H₂₃N₃O₄·H₂O, (I), the erlotinib hemioxalate salt [systematic name: 4‐amino‐N‐(3‐ethynylphenyl)‐6,7‐bis(2‐methoxyethoxy)quinazolin‐1‐ium hemioxalate], C₂₂H₂₄N₃O₄⁺·0.5C₂O₄²⁻, (II), and the cocrystal erlotinib fumaric acid hemisolvate dihydrate, C₂₂H₂₃N₃O₄·0.5C₄H₄O₄·2H₂O, (III). In (II) and (III), the oxalate anion and the fumaric acid molecule are located across inversion centres. The water molecules in (I) and (III) play an active role in hydrogen‐bonding interactions which lead to the formation of tetrameric and hexameric hydrogen‐bonded networks, while in (II) the cations and anions form a tetrameric hydrogen‐bonded network in the crystal packing. The title multicomponent crystals of erlotinib have been elucidated to study the assembly of molecules through intermolecular interactions, such as hydrogen bonds and aromatic π–π stacking.     

Sonofragmentation of molecular crystals

Possible mechanisms for the breakage of molecular crystals under high-intensity ultrasound were investigated using acetylsalicylic acid (aspirin) crystals as a model compound for active pharmaceutical ingredients. Surprisingly, kinetics experiments ruled out particle-particle collisions as a viable mechanism for sonofragmentation. Two other possible mechanisms (particle-horn and particle-wall collisions) were dismissed on the basis of decoupling experiments. Direct particle-shock wave interactions are therefore indicated as the primary mechanism of sonofragmentation of molecular crystals.     

Thermodilato-microscopy of liquid crystals

Liquid crystals exhibit successively several fluids and/or viscous phases and therefore microscopical methods play an important role for their characterization. No really efficient routine dilatometric method exist for rather small samples. By simple addition of a Michelson's interferometer objective and a photo-multiplier to the basic equipment for the investigation of liquid crystals — i.e. a polarizing microscope associated to a heating and cooling stage — dilatometric investigations as well as studies of phase transitions are getting accessible. In fact, when a droplet of liquid crystal, set up in a spherical stamp, is lightened through the interferometer with a quasi monochromatic source, equal thickness circular fringes are observable on the surface of the sample. A thermal expansion of the droplet leads to displacements of these fringes. The principle for the measurement of the volume changes consists by recording, versus the temperature, the variations of the light intensity of the central fringe. The volume of the sample, at given temperatures, is determined from photomicrographs of the whole interference feature. This volume is lower than 0.1 mm³. Experiments on the pure compound octyl-cyanobiphenyl show that the method is convenient for the detection of the phase transition, even if the transformation is weakly first order asS _A -N. Tested with a commercial ternary mixture the expansivity of phases and the transitions volumes changes can be deduced from experiments.

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Zusammenfassung Flüssige Kristalle besitzen mehrere flüssige und viskose Phasen, so dass zu ihrer Charakterisierung mikroskopische Methoden eine grosse Bedeutung besitzen. Zur Zeit besteht keine routinemÄssig einsetzbare dilatometrische Methode im Mikromassstab. Durch die Erweiterung eines Mikroskopes mit einem Interferometer nach Michelson und unter Einsatz eines Photoelektronenvervielfachers bei gleichzeitiger Verwendung eines Kühl- und Heiztisches werden sowohl dilatometrische Messungen als auch Untersuchungen von Phasenumwandlungen zugÄnglich.Es werden in der vorliegenden Arbeit Messungen an Oktyl-cyano-biphenyl und an einer ternÄren Mischung dargestellt und diskutiert.

     

高效液相色谱-旋光检测器联用实时检测对映体过量

在手性合成或拆分过程中,实时监测反应产物的对映体过量(e.e.)对于确定产物光学纯度至关重要。根据在一定测定条件下,单一对映体旋光度仅与其浓度成正比,利用高效液相色谱与旋光检测器联用,提出了一种实时测定e.e.的新方法。并在猪胰脂肪酶催化酯交换反应制备(S)-2-甲基-1-丁醇的过程中,比较了该方法与常规测定方法,证实了该方法简单,快速,有望作为一种手性技术中e.e.在线测定通用方法。     

The heat of fusion of polymer crystals: Polyethylene crystals in suspension

Recent experiments have supported the view that polyethylene (PE) single crystals kept in suspension, in a variety of liquids, have different physical properties compared with the same crystals after drying. The present work was undertaken in an attempt to directly measure one of the basic properties of crystals in suspension, namely their percent crystallinity (X). Differential scanning calorimetry was chosen as the primary tool for this investigation. A method has been developed to determine the weight of PE in a suspension of crystals in a nonsolvent. Thus, a determination of X can be made. For suspension crystals, X was found to be at least 88.5%, some 6% larger than that for the corresponding dried or freeze-dried material. Implications with regard to the fold-surface structure are discussed. Differences in degree of crystallinity as a function of drying procedure have also been observed.