Kinetics of phase separation in polymer blends for deep quenches

Electro microscopy was used to study the phase separation kinetics of a polystyrene/polyvinylmethylether system subjected to a critical deep quench. The size of the phase-separated domains was found to increase linearly with time, implying that hydrodynamic effects control the rate of growth of the domains in the time scale and temperature range under consideration. From these measurements the growth velocity and approximate diffusion constants can be determined for three different temperatures. Comparison of these results with those obtained by light scattering on other systems and with theoretical predictions is possible by replotting in dimensionless units.

Poly(styrene-b-methyl methacrylate) block copolymers as compatibilizing agents in blends of poly(styrene-co-acrylonitrile) and poly(2,6-dimethyl-1,4-phenylene ether): 1. Location of block copolymers in ternary blends — compatibilization versus micelle formation

Abstract The compatibilizing effect of the symmetric narrowly distributed block copolymer poly(styrene- b -methyl methacrylate) (P(S- b -MMA)) in blends of high-molecular-weight poly(styrene- co -acrylonitrile) containing 20 wt% (PSAN20) or 43 wt% acrylonitrile (PSAN43) with poly(2,6-dimethyl-1,4-phenylene ether) (PPE) was investigated by dynamic mechanical spectroscopy and transmission electron microscopy. In blends with the PSAN43, P(S- b -MMA) forms spherical micelles in the PPE phase with no dispersing efficiency. In contrast to this, for blends with PSAN20, the block copolymer is located at the phase boundary, causing an extremely fine dispersion of the components. Depending on the loc…

Poly(styrene-b-methyl methacrylate) block copolymers as compatibilizing agents in blends of poly(styrene-co-acrylonitrile) and poly(2,6-dimethyl-1,4-phenylene ether): 2. Influence of concentration and molecular weight of symmetric block copolymers

Abstract The influence of the molecular weight of the symmetric block copolymer poly(styrene-b-methyl methacrylate) (P(S-b-MMA)) in blends with high-molecular-weight poly(styrene-co-acrylonitrile) (PSAN) and poly(2,6-dimethyl-1,4-phenylene ether) (PPE) is investigated by dynamic mechanical analysis and transmission electron microscopy. Total molecular weights of the block copolymers vary from 16 up to 275 kg mol−1. Independent of molecular weight, all block copolymers locate to the interface with strong dispersing efficiency. The different block copolymers also showed approximately the same emulsifying efficiency. The degree of segmental mixing of the blocks with the respective phases is ev…

Relationship between microscopic and macroscopic structures of organic thin films for SHG

The experiments described in this paper were undertaken in order to obtain information about the relationship between the structure and non-linear optical properties (second-harmonic generation) of organic thin films. For this purpose, two closely related dyes, diones and tetrones, were compared, both of which are shown to have large hyperpolarisabilities. Their microscopic properties are investigated by conformational analysis and electron diffraction. It could be shown that detailed knowledge about the structure and the adjacent neighbour packing can be obtained from conformational analysis and electron diffraction in order to understand the non-linear optical properties of the two dyes.

Microstructure of a Discotic Polymer as Revealed by Electron Diffraction and High-Resolution Imaging

Structural investigation of four-centre photopolymerisation of bis-phthalamic bis-chalcone derivative in the crystalline state

By combining the results obtained from an electron diffraction tilting series with solid state NMR and powder X-ray diffraction, it was possible to determine the unit cell parameters and space group of BPABC crystals grown from DMAA solution both before and after irradiation. Subsequently semi-empirical quantum mechanical and packing energy calculations led to a model structure which agreed well with all the electron diffraction data and thus provided insight into the cross-linking mechanism. © 1997 John Wiley & Sons Ltd.

Synthesis and photodimerisation of tetrabenzo[ab,f,jk,o][18]annulenes

Abstract The tetrabenzo[ab,f,jk,o][18]annulenes 7a,b, generated in a 5-step synthesis, show photodimerisation and -oligomerisation reactions in the solid state and in solution. The state of aggregation determines the reaction route. Whereas the cyclodimer 8a has a simple cyclobutane structure, the dimer 8b is a highly symmetrical cyclophane.

ChemInform Abstract: Synthesis and Photodimerization of Tetrabenzo[ab,f,jk,o][18]annulenes.

Second harmonic generation in ferroelectric liquid crystalline thiadiazole derivatives

Numerical analysis of lamellar thickness distributions

Etude comparative des distributions d'epaisseur de cristallites dans des polyethylenes de masse molaire 10000-100000 cristallises presentant des distributions etroite, bimodale, asymetrique ou large, par microscopie electronique, diffusion RX centrale et spectroscopie Raman. Variations des resultats avec la morphologie des cristallites et surtout avec la nature de la distribution

Structure Determination by Electron Crystallography Using a Simulation Approach Combined with Maximum Entropy with the Aim of Improving Material Properties

Solving a crystal structure is only one of the many problems involved in the process of improving material properties. Because it is difficult to obtain large single crystals from most polymeric and many monomeric organic materials, it is essential to develop electron crystallography to make reliable crystal structure analysis possible.

Morphology of melt-crystallized linear polyethylene fractions and its dependence on molecular weight and crystallization temperature

Replicas and thin-section electron microscopic studies were made of fractions of linear polyethylene covering the molecular weight range 2.78 × 104 to 6.0 × 106 for a variety of crystallizing conditions. Lamellar crystallites were found under all circumstances; and the supermolecular structure, or crystalline morphology, is in agreement with that previously reported from an analysis of the small-angle light-scattering patterns of the same samples under similar crystallization conditions. Details of the crystalline microstructure are also described, which range from truncated hollow pyramids which degenerate as the molecular weight or the undercooling are increased. From these results, it is…

Electron crystallography and organic materials with non-linear optical properties

Results of electron microscopic studies of crystal structures of a number of bis-benzylidene cyclohexanones are presented. It is shown that some of these compounds are efficient crystalline non-linear optically active (NLO) chromophores with second harmonic generation (SHG) properties. Appropriately functionalized chromophores of this type can be used as a polycondensation comonomer to produce partly crystalline main-chain NLO-active polymers. Electron diffraction crystal structural data, obtained for very small crystals, allowed us to get reasonable estimations of macroscopic crystal NLO-coefficients, relating quantum-chemically calculated molecular first hyperpolarizability components to …

An attempt is made to correlate crystallographic changes arising during the radiation induced polymerisation of trioxane with the morphological changes observed during this process. Particular emphasis is placed on the differences which are noted with changing polymerisation time and temperature, so that both nucleation and growth could be discussed. Die Anderung der Kristallstruktur des Trioxan, die bei der strahleninduzierten Polymerisation beobachtet wird, wurde im Zusammenhang mit den bei diesem Prozes auftretenden morphologischen Veranderungen untersucht. Die Unterschiede, die sich durch geeignete Wahl der Polymerisationszeit und der Temperatur ergeben, bieten die Moglichkeit, sowohl d…

A comparison of the Raman LAM and electron microscopy in determining crystallite thickness distributions: Polyethylenes with narrow size distributions

Bon accord entre les resultats obtenus pour des polyethylenes cristallises a 118 o C pendant 2 et 20 minutes lorsqu'on prend en compte l'inclinaison de la chaine et pour des polymeres a distribution etroite

Use of transmission electron microscopy to obtain quantitative information about polymers

In the polymer field the electron microscope is frequently used as a tool for obtaining purely qualitative data, but only rarely to obtain quantitative information. In order to discuss the potential of this instrument for the latter purpose it is convenient to separate the discussion into the following sub-sections.

Feinstrukturanalyse eines diskotischen Polymers durch Elektronenbeugung und hochauflösende Elektronenmikroskopie

Comparison of electron diffraction data from non-linear optically active organic DMABC crystals obtained at 100 and 300 kV

During the recent past, we have synthesized a new class of molecules with intramolecular two-dimensional charge transfer upon excitation. The present report presents such a molecule, 2,6-bis(4-dimethylamino-benzylidene)-cyclohexanone (DMABC), with an unusually high value of the second-order non-linear optical (NLO) coefficients. In order to optimize the macroscopic NLO properties of the compounds, it is necessary to relate their first hyperpolarizability tensors at a molecular level to those at a crystal bulk level. This requires a complete structure determination and refinement. However, the growth of sufficiently large single crystals, which are needed for structural analysis and refineme…

Polymer microscopy, 2nd edition. by L. C. Sawyer, D. T. Grubb, Chapman & Hall, London 1996, xii, 397 pp., hardcover, £85.00, ISBN 0-412-60490-6

ChemInform Abstract: Electron Crystallography and Organic Materials with Non-Linear Optical Properties

Results of electron microscopic studies of crystal structures of a number of bis-benzylidene cyclohexanones are presented. It is shown that some of these compounds are efficient crystalline non-linear optically active (NLO) chromophores with second harmonic generation (SHG) properties. Appropriately functionalized chromophores of this type can be used as a polycondensation comonomer to produce partly crystalline main-chain NLO-active polymers. Electron diffraction crystal structural data, obtained for very small crystals, allowed us to get reasonable estimations of macroscopic crystal NLO-coefficients, relating quantum-chemically calculated molecular first hyperpolarizability components to …

The use of maximum entropy statistics combined with simulation methods to determine the structure of 4-dimethylamino-3-cyanobiphenyl

Abstract 4-dimethylamino-3-cyanobiphenyl (4-DMA-3-CB) was characterised with respect to non-linear optical (NLO) properties in the gas phase and in the crystal. The crystal structure was solved from a series of electron diffraction patterns using both molecular modelling and ab initio maximum entropy techniques combined with log-likelihood evaluation. The agreement between the two methods is excellent and the structure evaluation permits an analysis of the major components of the hyperpolarisability tensor in the crystal framework.

Strategies for structure solution and refinement of small organic molecules from electron diffraction data and limitations of the simulation approach

In recent years, a series of non-linear optically active bis(benzylidene) ketones have been synthesized and investigated by electron crystallography. In most cases, structure refinement was possible by combining electron diffraction analysis and quantum-mechanical calculations with maximum-entropy methods. However, when the torsional angles between the phenyl rings and the C=C double bonds are strongly affected by the crystal field, this method fails because packing-energy calculations are not sufficiently sensitive. This problem can be solved by refining the approximate model with SHELXL, if the data set is sufficiently accurate and the model close to the correct structure. Here it is show…

A quantitative electron-microscopic study of a linear polyethylene fraction crystallized at different temperatures

Replica and thin-section electron microscopy was performed on a linear polyethylene fraction (Mw = 1.89 × 105, Mn = 1.79 × 10 5) which was either isothermally crystallized or quenched at difference temperatures. The results are numerically analyzed in such a manner so as to give the distribution of the total long spacing and of the crystallite and amorphous thicknesses. The quantitative information about the maximum and minimum values for these parameters at each crystallization temperature yields important clues as to possible molecular processes involved. Qualitative information regarding general morphology, molecular tilt with respect to the lamellar surface, and possible crystallographi…

A quantitative electron microscopic study of the crystalline structure of ethylene copolymers

Etude de sections minces sur des fractions de composition de copolymeres cristallises dans des conditions extremement severes

Use of electron microscopy to obtain quantitative information about the melting behavior of branched polyethylene

The melting behavior of low-density polyethylene was studied by electron microscopy. The experimental techniques and method of evaluation chosen were such as to deliver quantitative numerical data. The values which could be derived from suitably prepared histograms were the minimum, maximum, average, and most probable values of the crystal thickness d and long-spacing L. All these values were in good agreement with small-angle x-ray scattering results. The histograms also show the distribution functions for d and L, so that effects leading to changes in the average values can be observed in detail. The results provide further support for a model of melting and crystallization proposed in a …

Studies of structures and properties of polymeric systems containing bis-(hydroxy-arylidene)alkanones as NLO-active chromophores

Abstract NLO-properties of polymer systems containing bis-(hydroxy-arylidene)alkanone chromophores were studied experimentally and analyzed using ab initio quantum chemical calculations. A monoclinic crystal structure (space group P2111) of the polyester containing fragments of such chromophores in the backbone was simulated and a reasonable agreement between the experimental and simulated X-ray powder diffraction patterns was achieved. Ab initio quantum-mechanical estimations of the SHG-observable macroscopic second-order non-linearity tensor coefficients, obtained for the polymer crystal structure at the HF SCF level, led to the major dXZZ-coefficient of 1.9 pm/V. Films of ionic complexes…

Structure determination to calculate nonlinear optical coefficients in a class of organic material

A class of molecules with intramolecular two-dimensional charge transfer upon excitation has been synthesized. It is expected that these materials should be prospective candidates for nonlinear optical (NLO) applications such as second harmonic (SHG) generation. In order to optimize the macroscopic NLO properties of the compounds, it is necessary to relate their first hyperpolarizability tensors at a molecular level to those at a crystal bulk level. This requires a complete structure determination and refinement. However, the growth of sufficiently large single crystals, which are needed for structural analysis and refinement by x-ray methods, is a time-consuming and sometimes impossible ta…

Oil-Water Interface Templating of Mesoporous Macroscale Structures

Ordered mesostructured porous silicas that are also macroscopically structured were created by control of the interface on two different length scales simultaneously. Micellar arrays controlled the nanometer-scale assembly, and at the static boundary between an aqueous phase and an organic phase, control was achieved on the micrometer to centimeter scale. Acid-prepared mesostructures of silica were made with the p6, Pm3n, and the P63/mmc structures in the form of porous fibers 50 to 1000 micrometers in length, hollow spheres with diameters of 1 to 100 micrometers, and thin sheets up to 10 centimeters in diameter and about 10 to 500 micrometers in thickness. These results might have implicat…

Structure analysis of side chain liquid crystal polymer films by means of electron microscopy

Abstract Using the combined techniques of electron diffraction, bright and dark field electron microscopy as well as light microscopy, it has been possible to obtain detailed structural information about the arrangement of the smectic layers in a polymethacrylate side chain liquid crystal polymer with a biphenylester as the mesogenic group.

Direct observation of smectic layers in side chain liquid crystal polymer films

Abstract By applying stringent conditions to the imaging process it has been possible to produce electron micrographs of the smectic planes in a highly beam sensitive polymethcrylate side chain liquid crystal polymer. These planes show a high degree of internal perfection, while, at the same time, showing clear evidence of curvature. The director orientation was determined over a fairly large region.

Model of partial crystallization and melting derived from small-angle X-ray scattering and electron microscopic studies on low-density polyethylene

A temperature-dependent small-angle x-ray scattering and electron microscopic study on a sample of low-density polyethylene affords a determination of the structure changes in a heating and cooling cycle and suggests a new model of partial crystallization and melting. The analysis of SAXS data is based upon some general properties of the electron-density correlation function. Electron micrographs are obtained from stained sections γ irradiated at elevated temperatures and are analyzed quantitatively by statistical means. According to the model proposed here the thickness distribution in the amorphous layers, rather than that of the crystalline regions, is the essential factor governing the …

A quantitative electron microscopic study of the crystallite structure of molecular weight fractions of linear polyethylene

Utilizing thin-section techniques, transmission electron microscope studies were performed on a series of bulk-crystalized fractions of linear polyethylene covering the range M = 5 × 103−6 × 106. The crystallization conditions were varied from long-time isothermal to rapid quenching. Quantitative analysis could be carried out on such samples crystallized under controlled conditions. The crystallite thickness distributions and long periods are presented in terms of histograms. From these data the degree of crystallinity can be calculated and was found to compare favorably with that from other methods. The amorphous thickness increases significantly with molecular weight for all modes of crys…

Chiral helical nanostructures based on amorphous abc-triblock copolymers

So far all lattices of regular microdomain structures reported in the literature, either based on binary AB, ABA or ternary ABC block copolymers, can be described using simple symmetry elements like mirror planes, symmetry centers and rotation axes. The microphase separation in a linear ternary block copolymer consisting of three immiscible components namely polystyrene, polybutadiene and polymethyl methacrylate gives rise to the formation of a chiral supramolecular assembly in which chirality is not defined on a molecular (or macromolecular) level but only by the assembly of the linear triblock copolymer molecules. The polybutadiene (7, 12 wt.-%) phase forms helical strands surrounding the…

The sanidic polyamide [NM-Ph(CO 2 R) 3 (CO 2 Me)-NMCO-Ph(OR) 2 CO] n (R=C 12 H 25 ) is studied. It is shown that this polymer has a biaxial structure with quasi 2-D long range translational correlations. The correlations in one direction are limited by the length of the molecule. The oriented regions are separated by regions in which the molecules are less oriented

Structural defects in smectic c* liquid crystals

In this paper the structure of a smectic c* liquid crystalline material which can be switched in an electric field is investigated by electron microscopic techniques. Using this method the director field is revealed and typical disclinations observed. Analysis of these features enables the elastic anisotropy of the material to be calculated. Sample description. For our structure investigations a liquid crystalline material (4-(3-(s)-methyl-2-(s)-chloropentanoyloxy)-4'-octyloxy-biphenyl) with two chiral centres was synthesised using known procedures [I]. This material has been investigated by broadband dielectric spectroscopy, the softand Goldstone modes were analysed [2a] as well as the hig…

Freely-Suspended and Transferred Freely-Suspended Films of Polymeric Liquid Crystals

Freely-suspended (FS) liquid-crystal (LC) films of a polymethylsiloxane homo- and a copolymer with different mesogenic side groups have been prepared and investigated. For both substances the preparation of the films succeeded only in the isotropic phase but the higher ordered phases were reached after cooling. The films of the homopolymer have only been obtained with thicknesses estimated to be in the pm-range and with an unusual “Book-Shelf” orientation of the smectic layers. In contrast, the films of the copolymer were thinner and showed a homeotropic orientation of the mesogens in the smectic A phase. Interestingly, this material exhibited a different layer spacing in film and bulk, alt…