Characteristics and flow behavior of molten tin-polypropylene blend systems

An experimental study of tin-polypropylene compounds involving melt mixing and melt extrusion and molding over a range of temperatures is described. Problems of coalescence which make continuous mixing impossible above the melting temperature are described. Significant coalescence of the tin also results in extrusion and injection-molding problems. The influence of tin content and melt temperature on shear viscosity and extrusion character is discussed and interpreted. The electrical properties of the compounds are investigated.     

The aggregation behavior of poly-(oxyethylene)-poly-(oxypropylene)-poly-(oxyethylene)-block-copolymers in aqueous solution

Aqueous solutions of blockcopolymers, consisting of a polyoxypropyleneblock (POP) with a polyoxyethylene-block (POE) at each side, were studied using surface and interfacial tension measurements, static and dynamic light scattering and smallangle neutron scattering techniques, electric birefringence, rheological and DSC-measurements. The compounds were commercial samples and had an approximate average composition EO₂₀PO₇₀EO₂₀, EO₁₈PO₅₈EO₁₈, and EO₁₀₆PO₆₉EO₁₀₆. All three compounds formed micelles above a critical concentration. The size of the micellar core is determined by the length of the hydrophobic poly-propyleneoxide block. The transfer energy of a propyleneoxide unit from the aqueous to the micellar phase is about 0.3 kT at room temperature and hence a quarter of the corresponding value for a CH₂-group.The aggregation number of the micelles increases strongly with increasing temperature while the hydrodynamic radius remains constant in first approximation. The smallangle neutron scattering (SANS) data show at higher concentrations a strong correlation peak. Both the SANS- and the light-scattering data can be interpreted on the basis of the theory of hard sphere particles.Solutions with a volume fraction beyond about 0.2 gellifie when the temperature is raised above a characteristic value that is at the lowest concentrations slightly above room temperature, shift to lower values with increasing concentrations. Below this gelation temperature DSC-measurements show a phase transition with enthalpies between 40J/g and 80J/g, which is probably due to the dehydration of the PO-groups; this transition can also be observed at low concentrations where no gelation takes place. The position of the correlation peak of the SANS-data is not affected by the gel formation. Some samples, however, show clear evidence of long-range order and seem therefore to consist of cubic liquid crystalline phases. The shear moduli of the gels can qualitatively be understood on the basis of hard sphere models.     

The dispersion of hydrophilic and hydrophobic flame-hydrolysed silicas in short-chained alkanols

The ultrasonic dispersion of Aerosil 200 and some n-alkyl surface-modified derivatives thereof in alkanols have been examined. The sizes of the aggregates formed during this process were investigated from measurements of sol viscosity and quasi-elastic light scattering (QELS). In the former technique, the aggregate volume ratios (AVR) were calculated at very low volume fractions of silica. The AVR values so obtained indicated that the silica monomers were highly aggregated in all systems, as expected. Differences between the various alkanols were found, however. Decreasing continuum polarity from water to hexan-1-ol produced decreasing AVRs. From hexan-1-ol to octan-1-ol, however, the AVRs increased. The n-alkyl surface-modified silicas gave AVRs substantially different to A 200, related most likely to wetting and solvation of the solid surface during dispersion. QELS measurements were subsequently found to be of limited use for these systems, since the aggregate size distributions in these sols were evidently very broad. The results indicated that these size distribution were non-Gaussian. The use of QELS to investigate systems of such high aggregation appears to be limited.     

A phenomenological model of photoprecipitation in a-Se colloid solutions

An attempt has been made in this study to develop a physical model for the photoprecipitation and photoaggregation effects in amorphous Se (a-Se) colloids. The theory explains in basic terms the experimental time dependence of the precipitated elemental Se concentration. Several kinetic parameters were evaluated by correlating the experiment to theory, subject to strong light intensity and narrow beam approximations. The results were used to quantify and clarify several further features of photoprecipitation in a phenomenological way.     

Small-angle neutron scattering of colloidal silica dispersions in a non-polar solvent

Small-angle neutron scattering studies were performed on dilute dispersions of colloidal silica spheres in mixtures of h₁₂- and d₁₂-cyclohexane. The particles consisted of a SiO₂-core and a layer of stearyl alcohol molecules terminally attached with a chemical bond (Si-O) to the particle surface. The contrast variation method was applied to reveal the internal structure of the particles. The matchpoints determined with this method were in accordance with those calculated from the mass density of the particles and the atomic composition, as determined with elemental analysis.For a detailed interpretation of the scattering curves, we assumed that the particles were spherosymmetrical and consisted of two concentric layers. With the relation we derived between the radius of gyration and the reciprocal contrast for such a model, it was possible to determine all the parameters characterizing the particle in terms of this model. The model calculations performed using these parameters fitted very well to the experimental intensities for high contrasts. For lower contrasts, the fit was somewhat less good. This is probably due to random fluctuations in the scattering length density within the particle core.The different radii as found by neutron scattering, agreed very well with those determined using other techniques, such as light scattering (static and dynamic) and electron microscopy.     

Structure relaxation after temperature jumps in homogeneous polystyrene/poly(styrene-co-bromostyrene) blends

Concentration fluctuations in polymer blends and their change after a temperature jump were studied by time-dependent small angle X-ray scattering experiments. Measurements were conducted on homogeneous mixtures of polystyrene and a partially brominated derivative. Structure factors in thermal equilibrium show the form given by the random phase approximation, thus enabling a direct determination of the-parameter and the mean radius of gyration. TheT-dependence of can be understood as the result of superposed enthalpic contributions and a free volume term. In theT-jump experiments, samples were quenched to temperatures near T_g. Relaxation occurs on the time scale of minutes and is nonexponential, becoming slower with time. Initial relaxation rates increase with increasing scattering vectorsq in accordance with theoretical predictions.     

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     

The preparation of monodisperse polyacrylonitrile particles in the presence of AB block co-polymers of poly-2-vinylpyridine/poly tertbutylstyrene

Radical dispersion polymerisation of acrylonitrile in cyclohexane was performed in the presence of the diblock copolymer poly-2-vinylpyridine/poly tertbutylstyrene, giving polymer latex particles stabilised by surface layers of chains of poly tertbutylstyrene. A seeded polymerisation route was employed and the addition of up to a further seven feeds of reactants resulted in the particle growth and the total volume fraction of particles increased to 0.2. The effect of varying the molecular weight of the stabiliser and stabiliser concentration was also investigated. Particle diameter in the range 40–150 nm were obtained depending on the condition of the polymerisation.     

Effect of ultrasound on the encapsulation of titanium dioxide pigment

In this paper we describe the effect of 20 kHz power ultrasound on the encapsulation of titanium dioxide pigment with poly (methyl methacrylate) in an otherwise conventional emulsion-polymerisation process. In all instances, sonication of the reaction during the mixing period led to an improvement in the extent and uniformity of the coverage of the pigment. Low-power ultrasound produced a more uniform coverage than high-power ultrasound, but the latter provided greater particle dispersion.     

Structure/property relationships in LCP/PEI blends revealed with a new selective etching process

An etching technique for making visible the morphology of blends composed of polyetherimide and a liquid crystalline fully aromatic copolyester (LCP) has been developed. The four organic solvents-tetrachloroethane, N-methylpyrrolidone (NMP), dimethylformamide (DMF) and dimethylacetamide (DMAc)-selectively etch the polyetherimide without attacking the LCP component. By adjusting the etching conditions to the respective conditions prevailing within the samples, all the four solvents yielded equally good results across the entire concentration range investigated (from 20/80 to 80/20 percent by weight of LCP/PEI).The viscosith of the LCPs decreases markedly with increasing shear rate. The large shear rate gradient from the mould edges to the centre results in different deformations of different volume elements within the melt. The resulting frozenin morphologies can be visualized with the new etching technique. This allows one to explain certain correlations between morphology and mechnical properties of the respective samples.     

Particle stickiness variations in colloidal dispersions investigated with small-angle x-ray scattering

Small-angle x-ray scattering experiments were performed on concentrated dispersions in benzene, of silica particles coated with octadecyl-chains. Such dispersions are known to exhibit short-ranged attractive particle-interactions which depend on the temperature. At sufficiently low temperature, the attraction gives rise to a reversible phase-separation. In the present study, use was made of this phenomenon to fractionate the system. By analyzing two different fractions, the role of polydispersity in the attractive behavior was investigated.For both original and fractionated material, scattering curves were measured using a Kratky-camera equipped with a stepscanning setup and monitor-detector. The concentrations investigated were 0.033, 0.363, 0.496, and 0.628 g/ml, at temperatures ranging from 25° to 52°C.     

Solvent-induced phase separation in polycarbonate blends PC/TMPC

Compatibility of the polycarbonates of bisphenol A (PC) and tetramethyl bisphenol A (TMPC) was studied in glassy films cast from CH₂Cl₂ at room temperature, and above the glass-transition temperature. Blends with different compositions and of different molecular weights were analyzed by DSC and small-angle neutron scattering (SANS). Solution studies were made with light scattering and microscopy. Some of the blend films were two-phased when cast at room temperature, but all films were one-phased in equilibrium above the glass transition. The SANS data demonstrated that phase separation in the cast films was not caused by inherent incompatibility of PC and TMPC, but was induced by the solvent CH₂Cl₂. The effect is caused by a closed miscibility gap in the ternary solution system PC/TMPC/CH₂Cl₂.     

Rigid-rod polymers with flexible side chains

Modeling studies were performed for a rigid-rod polyester with hexadecyloxy side chains (n=16) in order to simulate x-ray scattering curves in the medium angle scattering region (s=4 sin / from 0.2 Å^–1 to 2.2 Å^=t–1). The experimental ones were taken from a material obtained by cooling to room temeperature from the smectic mesophase at 150°C. The wide-angle x-ray diffractograms were calculated for given conformations and molecular arrangements using Debye's equation. The theoretical result thus obtained for a great variety of possible packing models and structures was compared to the experimental result. The size of the effective scattering region is found to be 61×18×52=6×10⁴ ų and consists of approximately five layers, each of which is composed of two rigid rods and 20 side chains. The planes form by the rigid rods, together with the side chains, have a distance of 3.6 Å, the distance between the rods being 26 Å. As the main result, it was found that the side chains form regions with a denser ordering (clustering). The interchain distance for side chains decreases in the regions from 5.3 Å to 4.8 Å.     

Small-angle x-ray scattering by crystalline polymer fibers 2. Investigation of the linear paracrystalline model using various materials

The linear position-sensitive detector is well-suited to measure quantitatively the distribution parallel to the fibre axis of the intensity of small-angle x-ray scattering (SAXS) by polymer fibres, except that in the case of four-point patterns their width is greater than that of the detector window. A method is described which overcomes this problem, and which has high angular resolution. Using this method, the variation of scattered intensity with angles from 0.3° to 2.5° has been measured for fibres of poly(ethylene terephthalate), nylon, and low density poly(ethylene) (LDPE), and compared with that predicted by the linear paracrystalline model. In all cases except LDPE, when the distribution of phase lengths was given by the Reinhold function, there was no significant disagreement between the measured and predicted scattering except for a very small range of angles on the low angle side of the peak intensity. With LDPE small but significant discrepancies were found at other angles as well, and these were worse if the symmetrical Gaussian distribution function was used. The method enabled quantitative parameters describing the morphology to be obtained. It is concluded that the morphology of the linear paracrystalline stack is consistent with the SAXS intensity distribution, and that the Reinhold function is a reasonable approximation to the distribution of phase lengths. A small modification so that this decays more rapidly at long lengths might be necessary to explain the scattering for all materials over the entire angular range and other small changes might be needed with LDPE, although the asymmetrical nature of the distribution must be retained.On leave from Department of Physics, University of Technology Malaysia, 81300 Sekudai, Malaysia.     

An attempt to describe non-specific interactions of polymer-polymer type in the plastisol dispersions of polyvinyl chloride

The problem of non-specific interactions between macromolecules of the polymer in dispersion media composed of the various plasticizers and the addition of modifying agent have been examined. The calculations have been made on the basis of the viscosity data. The limiting concentration of polyvinyl chloride PVC in dispersion, the coefficient of shape, the value of interaction parameter and-potential have been determined. The correlations between the mentioned quantities have been pointed out.     

Determination of the structure factor for concentrated silica dispersions using small angle x-ray scattering. II. Experiment

The structure factor of a number of silica suspensions in cyclohexane, with concentrations ranging from 0.01 to 0.714 gcm^–3, has been determined with small angle x-ray scattering, using a Kratky camera. The experimental structure factor is compared with a theoretical one for which polydispersity effects on the particle scattering factor and on the structure are explicitly taken into account.Analysis of the scattered intensity at a scattering angle=0 shows that the particles in the suspension interact like hard spheres, with a specific hard sphere volume of 0.61 cm³g^–1. A comparison of the experimentally determined structure factor with the structure factor found by a model calculation for a polydisperse system, using the experimental particle size distribution, showed a general agreement. The height of the first maximum agreed well for all concentrations, however its position varied stronger with concentration in the experimental curves. A possible explanation of this effect is given.     

Self-diffusion of polystyrene in solution 2. Discussion of experimental results on the basis of the reptation mechanism and entanglements

The expressions for polymer self-diffusion in semidilute solutions, theoretically derived from the reptation mechanism, the blob concept and scaling considerations, are discussed and compared against experimental data from the authors' investigations and the literature. In the nonentangled (from viscoelastic data) semidilute solution, the experimentally observed concentration and molar mass exponents are in fair agreement with those derived theoretically. However, a quantitative estimation shows that the experiments cannot be explained by reptation. Experiments with polymer mixtures also give strong evidence against reptation. It is concluded, that in the nonentangled semidilute solution, the polymer self-diffusion is more complicated than simple reptation. This is also supported by recently observed long-range density fluctuations or cluster formation in this concentration region detected by scattering techniques and NMR-PFGT. In the entangled semidilute solution, the self-diffusion data are in accordance with the reptation mechanism; reptation being within a tube having approximately 20 blobs between entanglements.     

The pH dependence of dispersion of TiO2 particles in aqueous surfactant solutions

The pH dependence of dispersion of titanium dioxide (TiO₂) particles has been examined in the presence of surfactant molecules in water. Whereas particles were dispersed in water at acid and alkaline regions rather than at neutral region, the dispersion was enhanced at neutral region in an aqueous sodium dodecyl sulfate (SDS) solution and at acid and alkaline regions in an aqueous dodecyldimethylamine oxide (C₁₂DAO) solution. Considering the pH dependence of zeta potential, the adsorption models of surfactant molecules on a particle were estimated on the basis of the modes of hemimicelle and double-layer compression. While the particles that adsorbed Al³⁺ were remarkably dispersed around pH 6, their dispersion does not largely depend on pH in the addition of SDS, indicating the adsorption of SDS molecules to form double-layer compression in the whole pH region. Dynamic light-scattering measurement and electron microscopic observation suggested that the particles were dispersed in water as small flocs.