Morphology of solution crystallized trans-1,4-polyisoprene

The film formation method has been successfully used to grow single crystals and other complex morphological features of low melting form (LMF) and high melting form (HMF) of trans-1,4-polyisoprene (TPIP). Below 40 °C dilute amyl acetate solution gave hexagonal shaped LMF crystals. Thick and elongated hexagonal shaped morphology was shown by HMF crystals at temperatures above 40 °C. Straight faces and sharp corners of the single crystals, and also of complex crystals, acquired round shapes when highly polydispersed TPIP was used for crystallization.     

X-ray scattering by black foam films

The x-ray scattering by the three types of black foam films (common black, Newton black, and stratified black films) was experimentally studied. A special device in which flat black films with an area of ca. 2 cm² can be produced was developed and x-ray diffraction patterns were obtained by a vertical diffractometer. The three types of films differ significantly in their x-ray reflections, which proves that they have different structure. For common black films, the comparison of observed and calculated intensities lead to a model, which corresponds to the three-layer model. The Newton black films exhibit diffraction trace with only one highly asymetric peak and there is, as of yet, no unambigous interpretation. The patterns of the stratified black films have several pronounced sharp peaks corresponding to the areas of different films with a given thickness.     

Growth of polyethylene single crystals from the melt: change in lateral habit and regime I–II transition

Using the technique of extraction, single crystals have been obtained from polyethylene fractions isothermally crystallized from the melt at atmospheric pressure. It has been found that the lateral habit of single crystals changes in the vicinity of the transition temperature of growth regime (regime I–II): lenticular shape elongated in the direction of theb axis (type A) in the range of regime I and truncated lozenge with curved edges of {200} and {110} growth faces (type B) in that of regime II. The transition of lateral habit causes a drastic change in the width of {110} growth faces; {110} growth faces are well developed in type B crystals while they cannot be observed and must be very small in type-A crystals. It has been shown that the growth regime of the small {110} growth face of type-A crystals must be in regime I; hence the regime I–II transition can be explained as the result of this change in lateral habit (width of the {110} growth face).     

Formamide,a water substitute XIV (1) waterless microemulsions 8. Structural analysis by X-ray scattering of CTAB aggregates in formamide and in the microemulsion system (formamide,CTAB, isooctane, 1-butanol)

X-ray scattering was used to analyse the structures of aggregates of CTAB in various formamide-containing media.Firstly, CTAB micelles were detected in formamide solutions. A spherical micelle model was proposed; at values close to the CMC, smaller micelles were observed in formamide than in water.Secondly, the structure of microemulsions in the isooctane-rich zone of the system (formamide/CTAB=2, isooctane, 1-butanol) was studied by X-ray scattering. The structure was found to be quite different in this zone from that normally observed in aqueous microemulsions. Structures compatible with small filaments of formamide were detected. The results were related to previous measurements of electrical conductivity.     

Discussion of craze formation and growth in amorphous polymers in terms of the multiplicity of glass transition at low temperatures

A craze, the typical deformation zone in an amorphous polymer, can be divided into a precraze and a proper craze. A better understanding of the two corresponding formation processes is possible in terms of glass transition multiplicity.The precraze is associated with the molecular mobility in the confined flow zone, which is part of the main transition. The proper craze corresponds to the mobility in the flow transition zone (terminal zone for shear). A negative pressure generated by nonuniaxial stress is considered to be important for the maintainance of the molecular mobility in these zones belowT _g . The behavior of the zones at negative pressure and low temperatures Tg is considered using a pressure-temperature diagram. The fibril structure of crazes is discussed by a defect diffusion model for the proper glass transition; it is correlated with the sequential physical aging of the corresponding frozen structural defects. Typical mode lengths of the molecular mobilities in the different zones are compared with typical craze parameters. The structure of the craze material is considered to result from confined flow processes which cannot percolate because in the main transition the flow is confined by entanglements, and in the flow transition zone the flow is stopped by releasing the negative pressure due to crack propagation.     

Determination of dispersive and nondispersive components of the surface free energy of glass fibers

The dispersive component _s ^d of the surface free energy of glass fibers and its interaction energy with alkanes, benzene, 1-nitropropane, ethyleneglycol, glycerol, formamide, and water were quantitatively determined by the tensiometric method within two liquids. The values of nondispersive interaction energy I _SL ^p were found to be a linear function of the square root of the nondispersive component of the surface free energy of liquids. This suggests that the nondispersive interaction energy may be represented by the geometric mean of the nondispersive component of the surface free energy of a solid and a liquid. The slope gave the nondispersive component _s ^p of the surface free energy. The _s ^p values are 33 and 14 mJ/m² for the untreated and aminosilane-treated fibers, respectively, suggesting that organophilic character has developed on the surface after aminosilane treatment. The _s ^p value was almost similar after the treatment, probably because of the polar characteristics of amino groups.     

In situ SAXS investigations of isothermal crystallization in poly(TMPS) fractions

The isothermal crystallization kinetics of poly(TMPS) has been measured by ISSAXS and results obtained for a molecular weight fraction (21,000) below the critical entanglement molecular weight (25,000) and another one above it (371,000). The SAXS intensity vs. time curves suggest that a single transformation mechanism exists. The SAXS long period is independent of crystallization time for both poly(TMPS) fractions. However the interlamellar thickness contribution to the long period is dependent upon molecular weight and crystallization temperature, increasing with temperature and molecular weight. The crystallite contribution also increases over the range studied. Both fractions exhibit a significant, but reversible decrease in thickness on cooling the sample from the crystallization temperature to room temperature and recyling again. The change is more pronounced for 371,000 specimen in keeping with its lower crystallinity. The path dependence of lamellar dimensions has significant implications in the morphological characterization of polymers annealed or crystallized at one temperature and then measured at another one.Paper presented at the American Physical Society March 25–29, Baltimore, MD (1985).     

A study of the ageing of the gel structure in a nonionic O/W cream by X-ray diffraction,differential scanning calorimetry and spin-lattice relaxation measurements

The time dependent changes of the lamellar gel structure in a nonionic O/W cream were studied. It appeared that the changes were connected with alterations in the hydrophilic layers of this lamellar gel structure. The structure of the hydrocarbon layers did not change. The alterations were induced by an increasing hydration of the surfactant molecules on cooling from the preparation temperature to room temperature. Ageing of the cream involves a decrease of the thickness of the hydrophilic layers and a change of the distribution of the surfactant molecules, resulting in, among other things, a decrease of the release rate of a hydrophilic drug. Ageing of the cream can be prevented by using the appropriate amount of starting materials or by the use of polymerizable surfactants. In the former case a cream, from which a drug is slowly released, is obtained. On the other hand, creams containing polymerized surfactants can release drugs at a relatively high rate.     

Temperature dependence of microhardness in the 70/30 polyvinylidene fluoride-trifluorethylene copolymer: New structural aspects of the curie transition

A combined X-ray diffraction and microhardness investigation of the 70/30 polyvinylidene fluoride-trifluorethylene copolymer was carried out as a function of temperature. The changes in microhardness are interpreted in terms of variations in lattice spacing of the ferro- and paraelectric phases, crystallinity and long period. The changes of microhardness with temperature show four distinct temperature regions. In addition to a low temperature range, in which microhardness decreases exponentially with temperature, the ferroparaelectric Curie transition involves a faster hardness decrease. At higher temperature, the sudden microhardness rise is ascribed primarily to an increase of crystal thickness within the remnant paraelectric phase. Near the melting point, the fusion of thinner crystals leads to a range in which microhardness decreases exponentially again.     

Deformation behavior of oriented UHMW-PE fibers

The mechanical behavior of gel-spun, ultra-drawn, UHMW-PE fibers was investigated as a function of temperature, stress, and time under static and dynamic loading conditions. From a phenomenological point of view, two separate contributions to the deformation behavior could be distinguished, i.e., a reversible (viscoelastic) contribution and an irreversible plastic flow component. It was investigated whether or not this distinction can be rationalized on a molecular basis. The fibers were studied using static (creep) and dynamic mechanical analysis (DMA), dilatometry, and wide-angle x-ray scattering (WAXS). The results of the combined experimental observations are discussed in an attempt to relate the deformation behavior of highly oriented PE fibers to events occurring on a molecular scale.     

An evaluation method for SAXS-patterns of fibrillar two-phase systems containing oriented particles of moderate anisotropy and short range correlation

Starting from the theoretical background of Rulands interface distributions, an evaluation method for small angle x-ray patterns arising from oriented fibrillar two-phase structures is proposed. If the fibril contains highly oriented particles with only moderate anisotropy and if the correlations between those particles within the fibril are of short range only, every axial section of the scattering pattern shows a one dimensional Porod law. A procedure of successive model confinement using the well known tools of nonlinear regression analysis is described. The result of such an analysis for the scattering pattern of an oil diluted SBS block copolymer recorded with synchrotron radiation under first-cycle stretching is reported. At=4 nm four contributions to the scattering pattern could be identified: a) fibrils containing well-defined cylinders standing upright; b) fibrils containing lying cylinders under destruction; c) stretched-out polybutadiene chains, connecting two polystyrene cylinders and causing the observable layer line pattern; and d) stretched-out polybutadiene chains looping through the neighboring PS domain and returning to their starting domain. In addition, a simple method for determining the height-to-diameter ratio of cylinders from the form factor envelope is proposed.     

Further electron microscope observations on polyethylene I. Granule structure of the melt as an artifact

There are still two opinions on the fine structure of polymer melts and glasses: (a) that the structure is similarly homogeneous to that in lower molecular weight materials and (b) that the structure shows larger short-range order regions (2–20 nm), which consist of bundeled segments of the chain molecules. Whereas opinion a relies more on indirect methods of investigation, opinion b is based mainly on fine granular structures which become visible in electron microscope investigations of surfaces of glassy solidified polymers. Such a fine structure can now be observed directly in a polyethylene melt. However, the structure is exposed as an artifact, so opinion a is supported.Dedicated to Prof. Dr. R. Bonart. Presented at the colloquium on 18.1.1985 in Regensburg on the occasion of his 60th birthday.Presented at the 32nd Meeting of the Colloid Society and Berlin Polymer Conference 1985, 2.–4.10.1985 in Berlin.     

Film formation with latex particles

The coalescence of latex particles is investigated through small-angle neutron scattering and electron microscopy. The particles are made of a soft polymeric core protected by a hydrophilic membrane, and they are dispersed in water. This dispersion is spread on a substrate, and water is removed to form a dry film. As the membranes of neighboring particles come into contact, they may break up to allow fusion of the particle cores. This is found to occur when the membranes are made of short-chain surfactant molecules; then all hydrophilic material is expelled to the film surface or to large isolated lumps. Alternatively, the membranes may remain until the film is completely dry; this is found to occur when they are made of hydrophilic polymers which are grafted onto the core. Hence, the fusion of particles is controlled by the connectivity of membranes.This work used the neutron beams of ILL in Grenoble and LLB in Saclay     

Effect of the reaction conditions on the degree of substitution of carboxymethyl cellulose

Cellulosic fabric composed of 84 % cotton and 16 % viscose rayon fiber was carboxymethylated. The influence of the reaction parameters (concentration of the reagents, time of reaction) on the degree of substitution was studied in the process, applying sodium hydroxide and monochloroacetic acid in one bath. Two kinds of regression equations were used to calculate approximately the degree of substitution. These polynomials can be used for the selection of reaction parameters to obtain a sample of a given degree of substitution.     

Characterization of wood fibers modified by phenol-formaldehyde

Wood-fiber phenol-formaldehyde-resin (PFR) modified surfaces, obtained from the adsorption of a PFR/water solution, are investigated as a function of the nature and the amount of PFR adsorbed. Surface are measurements are performed by using krypton adsorption at 77 K. Chemical modification is monitored by the electron spectroscopy for chemical analysis (ESCA) technique and the surface energy by the inverse phase gas chromatography (IPGC) method at infinite dilution. The London dispersive componentγ _S ^L of the surface energy shows a relationship to the concentration of carbon and oxgen at the fiber surface.γ _S ^L increases from 27.5 mN·m⁻¹ for the untreated fiber to 42.5 mN·m⁻¹ for the fibers treated with 20% high molecular-weight-grade phenol-formaldehyde. The surface atomic ratio O/C determined using the ESCA technique exhibits a decrease from 44% for untreated to 31% for treated samples. Surface area also decreases from 2.09 m²/g to 1.50 m²/g. The PFR adsorbed by wood fibers is observed as the dispersive component of surface energy starts to increase, as the surface oxygen concentration decreases, and on the surface area of the wood fiber.     

Mechanical properties and molecular mobility in oriented polyolefines

The static modulus of elasticity (E) and the correlation time of rotation ( _c ) of 2,-2,6,6-tetramethylpiperidine-1-oxyl are studied as a function of the temperature (210<T <350°K) for oriented films of isotactic polypropylene and polyethylene of high and low density.E and _c change both upon heating and polymer orientation; this result indicates that sample properties are influenced by the microstructure of the amorphous phase where probes are localized.     

Contact angle hysteresis in carbon fibers studied by wetting force measurements

The surface free energy of polyacrylonitrile carbon fibers was investigated by using the Wilhelmy technique. The difference in surface free energy between immersion and emersion was observed for the carbon fiber pyrolyzed at 2500 °C.In contrast, the hysteresis disappeared with repyrolyzation of the carbon fibers at 3000 °C. Auger electron spectroscopic analysis indicated that the surface of the latter carbon fiber (repyrolyzed at 3000 °C) consisted of the basal planes of graphite. Rough surface topography of the carbon fiber repyrolyzed at 3000 °C, as observed by scanning electron microscope, did not affect the hysteresis. Therefore, the contact angle hysteresis was attributed to the chemical adsorbants on the activation sites of the fiber surfaces, as detected by Auger electron spectroscopy.     

The effect of coating on the stiffness and toughness of encapsulated fiber composites

The effect of the coating of the fiber on the stiffness and toughness of composite materials is presented in this paper. The type of composite material considered is of a macroscopically isotropic composite medium containing coated fibers. The models used to simulate such materials consists of: the cylindrical fiber, a cylindrical annulus of the coating, an annulus of the matrix enveloped by an infinite region of an equivalent composite consisting of a transversely isotropic material and representing the real composite with dispersed coated fibers. Solutions for the longitudinal, transverse and shear elastic moduli in the four-phase model were established assuming linear elastic conditions. The results were found to depend on the extent and the mechanical properties of the coating. The stiffness and toughness of the composite were evaluated in models representing plane-stress equatorial sections of the representative volume element of the real material according to the Hashin-Rosen model. The stiffness of the fiber composites was studied by varying the rigidity and the extent of the fiber-coating in the model and evaluating its influence on the overall mechanical behavior of the model. On the other hand, the toughness of the composite was evaluated by the method of caustics in models made of composite PMMA plates with PMMA inclusions coated with a ductile annulus. Interesting results were derived concerning the influence of the soft annulus on the mechanical behavior of the composite.     

The exact shear modulus of particulates based on the concept of mesophase

An accurate relationship for the shear modulus of particulates is derived based on the Kerner model, but not using its approximate relations. Furthermore, the model takes into account the existence of the mesophase layer between the inclusions and the matrix, which acts as a smooth transition boundary layer between constituent materials. By applying Christensen's field to the Kerner model, modified by introducing the mesophase, the new model is liberated from any inconsistencies. Experimental evidence and application to a glass particle-epoxy resin-matrix composite indicated the superiority of the model over previous ones.     

Thermodynamic consideration on the interface formation of water and ethylene glycol isobutyl ether mixture

The interfacial tension of the binary two-phase mixture of water and ethylene glycol isobutyl ether (EIB) was measured as a function of temperature in the vicinity of the lower critical solution temperatureT _c under atmospheric pressure. The interfacial tension decreased with decreasing temperature and approached zero atT _c . The thermodynamic quantities of interface formation were evaluated by applying equations developed previously to the interfacial tension vs temperature curves. The results were compared with those of the water and diethylene glycol diethyl ether system examined previously, and the effect of the molecular structure of the ether molecule on its interfacial behavior was discussed. It was suggested that the hydration of the ethylene oxide groups of ether molecules was an important factor in the interface formation as well as in the mixing of component molecules of the systems investigated here.