TRANSPARENTE POLYMERE MEHRPHASENSYSTEME

Usually two phase polymer blends are not transparent because of differences in the refractive indices of their components and the resulting light scattering. By means of model calculations on the basis of the Mie-theory, the conditions for transparency in two-phase polymer blends are investigated. The models used are homogeneous spheres or spheres with a core-shell morphology imbedded in the polymer matrix. The light scattering of these particles is calculated as a function of diameter, refractive index, wavelength and particlecomposition. Results are presented that show the limits of diameter and difference in the refractive indices between matrix and particle for homogeneous particles to obtain transparency. In the case of large differences in the refractive indices or of large diameters the use of spheres with a core-shell morphology is favourable. Depending on the refractive indices of the respective phases, there exists an optimal composition of these spheres to obtain transparent polymer-blends. Another way to transparency is the minimization of light scattering by interparticle interferences, which can be achieved by special types of block-copolymers.     

Interpreting the appearance of dispersed systems: II. A guide for surfactant systems

We first analyze how color and transparency are perceived. Drawing on principles of light scattering investigated in Part I, we suggest simple rules and procedures in a diagnostic form for visually observ-ing fluid surfactant systems to estimate sizes of dispersed particles. Rules and procedures are organized into a guide, the use of which we illustrate by observing certain important surfactant systems. We conclude that it is possible to estimate particle sizes in the Rayleigh, Rayleigh-Debye-Gans, and Mie scattering regimes from such observations alone.     

高分子合金的力学性能与分散粒子径的关系

本文讨论了高分子合金中的平均分散粒子径d、粒子间距离与力学性能间的关系,当d小于临界平均分散粒子径d_c(dd_c时,冲击强度明显下降;在d=d_c附近,高分子合金的冲击强度发生急剧变化;分散相粒子间距离τ及其临界值τ_c对冲击强度的影响与平均分散粒子径的作用相似。同时,本文分析了影响分散形态的因素。     

Light scattering studies of hi-impact polystyrene

Small-angle light scattering techniques have been used to evaluate the factors controlling the transparency of two hi-impact polystyrene films. These factors were found to include surface smoothness, volume fraction of the phases in the system, the difference of the refractive indices of the phases, and the sizes of the phases. The elongation of the rubber phase during processing was also determined.     

Transparency of polymer blends

Polymer blending is useful for improving physical properties. Blends of transparent polymers are generally hazy. However, transparency is required in many products such as packages (especially PET bottles). The miscible blends, PET (polyethylene terephthalate)/PBT (polybuthylene terephthalate), maintain transparency in almost all cases regardless of the blending ratio, whereas the immiscible blends, PET/MxNYLON (MXD6 nylon, i.e. polymethaxylirene adipamide) and PET/PMAI (polymethacril imide, i.e. N‐methyl dimethyl glutarimide) become hazy as the blending ratio increases. The reason for this haze is the number and size of the dispersed particles. Differences in the refractive indices of various polymers also have a large influence on haze. Stretching makes even the transparent blends hazy in the case of PET/MxNYLON. One reason for this phenomenon is that stretching increases the size of the dispersed particles in the sheet plane. A second reason is that the difference in the anisotropic refractive indices of the matrix and the dispersed phase is increased by stretching. These effects are very consistent with light scattering theory.     

Optical properties of particle‐filled polycarbonate,polystyrene, and poly(methyl methacrylate) composites

Transparency is a key material property of polycarbonate (PC), polystyrene (PS), and poly(methyl methacrylate) (PMMA). To study the optical properties of particle‐filled PC, PS, and PMMA, composites containing inorganic particles in different sizes and concentrations were produced by direct melt mixing in this work. The optical properties characterized by total light transmittance, haze, and clarity were studied. The results show that the optical properties of polymer composites are strongly affected by particle content, particle size, and especially by difference in refractive indices between polymer matrix and particles. It is also revealed that the light transmittance and haze of composites are mainly affected by difference in refractive indices, whereas the clarity is more affected by particle size. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Calibration Correction of an Active Scattering Spectrometer Probe to Account for Refractive Index of Stratospheric Aerosols: Comparison of Results with Inertial Impaction

Real-time particle size spectra are being acquired on our research aircraft with relative ease and speed by techniques that make use of the real-time interaction of laser light with aerosols and cloud droplets. The results are, however, sometimes ambiguous, because the optical “signatures” of the particles depend on their refractive indices in addition to physical dimensions. The calibration supplied by the manufacturer is based on instrument response to a specific test aerosol, e.g., latex spheres (refractive index = 1.59). Such a calibration is strictly valid only for sample aerosols of refractive index and shape similar to the test aerosol. Whenever the sample aerosol differs from the test aerosol, a calibration correction is in order. Of concern here is the use of an active scattering spectrometer probe (ASAS-X), to measure sulfuric acid aerosols on high-flying U-2 and ER-2 research aircraft. Correcting the calibration of the ASAS-X for dilute sulfuric acid droplets (refractive index = 1.44) that predominate the stratospheric aerosol changes the inferred sizes by up to 32% per size interval from that determined from the nominal calibration. This results in an average increase in particle surface area and volume of 42 ± 10% and 71 ± 19%, respectively. The calibration correction of the optical spectrometer probe for stratospheric aerosol is validated by independent and simultaneous sampling of the particles with impactors. Sizing and counting of particles on microphotographs of scanning electron microscope images give results on total particle surface areas and volumes. After the calibration correction, the optical spectrometer data (averaged over four size distributions) agree with the impactor results (similarly averaged) to within a few percent. We conclude that the optical properties, or chemical makeup, of the sample aerosol must be known for accurate size analysis by optical aerosol spectrometers.     

Effect of morphology and refractive index on toughness and clarity balance of MBS modified vinyl bottles

Impact modifiers are used to enhance the toughness of rigid vinyl by providing a dispersed rubbery phase to absorb impact energy and prevent fracture of the otherwise brittle matrix. MBS impact modifiers are complex core//shell polymer structures based on specially prepared butadiene/styrene rubber latices with multiple stages of acrylic and other polymers grafted to them. In addition to providing a rubbery dispersed phase to improve to improve the toughness of vinyl, these structures also maintain clarity by matching the refractive index of the rubber particles with that of the vinyl matrix. Data will be present showing the effect of the rubber morphology, particle size and refractive index on the balance of impact strength and clarity of MBS modified vinyl packaging formulations.     

An Assessment of the Applicability of Particle Light Scattering Theories to Birefringent Polycrystalline Ceramics

The applicability of particle light scattering theories to light attenuation in birefringent polycrystalline ceramics was investigated by measuring light transmittance in a model two‐phase system. The system consisted of microspheres of silica dispersed in a solution of glycerol in water. The composition of the liquid medium was chosen to produce a mismatch between the refractive index of the particles (n_p) and of the medium (n_m) equal to the root mean square of the refractive index variation in polycrystalline magnesium fluoride. The variations of the scattering coefficients (γ) with volume fraction of silica microspheres for three different particle diameters (0.5, 1.0 and 1.5 μm) were compared with theoretical predictions based on scattering efficiency of single particles (K) and linear extrapolation to multiparticle dispersed systems. The measured scattering coefficients were significantly greater than the theoretical values for particle volume fractions greater than 0.2. These results suggest that application of particle scattering theories to a birefringent polycrystalline ceramic, an intrinsically high volume fraction system, is tenuous at best.     

Optical properties of dense and porous spheroids consisting of primary silica nanoparticles

The light scattering by granular and macroporous silica spheroids consisting of nanometer-sized primary particles was systematically investigated using a laser particle counter coupled with a pulse height analyzer. The shape- and porosity-controlled spheroids as model particles were prepared using spray drying method by changing the particle size of colloidal suspension. The effect of shape and porosity of dense and porous spheroidal particles on electrical mobility was also studied using a differential mobility analyzer and an electron microscope. The electrical mobility equivalent diameter of particles classified by the differential mobility analyzer was estimated by measuring Feret diameter and the projected area equivalent diameter from the SEM micrographs. The electrical mobility diameter of the spheroids was in good agreement with the projected area equivalent diameter regardless of the primary particle size and porosity. The measured partial scattering cross section of dense and porous silica particles with same mobility diameter showed significant differences. As the primary particle size of granules and the porosity of porous particles increased at parity of electrical mobility diameter, the scattering intensity decreased. The effective refractive indices of dense and porous particles were computed by best fitting of the scattering intensity measurements. The porosities of dense and porous spheroids were calculated using the effective refractive indices as obtained by the effective medium theory. The porosities were also measured by a comparison of particle size before and after annealing at 1700°C. By comparing these porosities, the effective refractive indices of the spheroidal particles were confirmed.     

Rubber toughened and optically transparent blends of cyclic olefin copolymers

A study is presented of increasing the toughness of Cyclic Olefin Copolymer (COC) while maintaining its optical transparency. The COC consists of a random copolymer of ethylene and norbornene, and the impact modifiers consist of thermoplastic elastomers. It is shown that several requirements must be satisfied, namely: for toughening there is an optimum finite particle size, but in order to minimize light scattering the particles have to be as small as possible. In addition, the refractive index of the elastomer must be closely matched to COC over the visible wavelength range and use temperature. Also for toughening, there are additional requirements of the adhesion of the elastomer to COC and high molecular weight. It is found that styrene butadiene styrene (SBS) is the most effective elastomer in toughening COC while maintaining optical transparency. It is also found that the addition of an index matched styrene‐ethylene‐butylene‐styrene (SEBS) copolymer as a compatibilizer to the SBS elastomer is beneficial in increasing the toughness and lowering the optical haze. Finally, light scattering calculations are presented based on the Rayleigh Debye model to calculate the optical haze and transmission of these blends. These calculations take into account the refractive index of COC and the elastomer, the particle size distribution and volume fraction of the elastomer. It is shown that there is reasonable agreement between calculation and experimental results. It is possible to increase the toughness of COC to greater than 50 J/m (Notched Izod) while keeping the optical haze to below 5% with an elastomer loading of 5% (w/w). We also identify opaque blends of COC with a toughness of greater than 500 J/m with an elastomer loading of 20% (w/w).     

Design of particulate composites for optical applications

This paper reviews the basic theoretical approach to describing light scattering in filled materials with nearly matching refractive indices (Rayleigh-Gans-Debye Theory). The modifications necessary to handle high filler concentrations (interparticle interference and multiple scattering) are included empirically. The primary result of this analysis is an expression for the optical transmission of a polymer composite as a function of particle size, volume fraction, composite thickness, and refractive index difference between the components. The angular dependence of the scattering is included so that scattered light which falls within the aperture of the transmission detector can be accounted for, Particular attention is given to including the temperature dependence of the refractive index and the effect of fillers on the thermal expansion properties of the polymer matrix in order to predict the temperature range over which the composite will be optically useful. Similarity to analyses of the Christiansen filter is discussed.     

Morphological study on the effect of elastomeric impact modifiers in polypropylene systems

The morphological effect of elastomeric impact modifiers has been studied in polypropylene systems by wide-angle and small-angle X-ray diffractometry, small-angle light scattering, light and electron microscopy and differential scanning calorimetry. It was established that the incorporation of an impact modifier altered the superstructure of the polypropylene matrix by decreasing the average size of spherulites through which the impact strength of the composite may be influenced. The changes in the mechanical and thermal properties are probably caused by the interphase between the amorphous elastomeric modifier and the polypropylene spherulites. The particle size of the dispersed elastomer is of vital importance in toughening of the amorphous polymer while in the crystalline resin, the changes in the superstructure also seem to be very important. Above T_g, the amorphous impact modifier acts as an energy absorber which markedly influences the crazing susceptibility of the polypropylene matrix.     

Untersuchungen an kautschukmodifiziertem PVC

The composition-morphology-property relationships are investigated for a series of ABS-, MBS- and AMBS-graft copolymer blends with PVC. The dispersibility of the graft copolymers in PVC improves with increasing grafting levels, while both impact resistance and tendency to stress whitening decrease. With respect to particle size, an optimum in the properties is found for particles of 200 nm. The grafting composition in ABS polymers giving the best results is a 75 S/25 AN copolymer, which is highly compatible with PVC. This high compatibility coincides with the good agreement between the solubility parameters for this SAN copolymer (δ = 9,8) and PVC (δ = 9,6). In MBS polymers increasing styrene levels lead to more transparent blends with PVC because of better matching of the refractive indices. However, impact strengths decrease at the same time because of deteriorating compatibility. Methyl methacrylate, having just the opposite effects to styrene, can be favourably used in combination with styrene or SAN by a stepwise addition of the graft monomers which is shown to result in optimum properties for MBS or AMBS polymers. Electron micrographs of the stress whitened areas reveal that the degree of crazing is negligible in comparison to other rubber modified thermoplastics. Instead of crazes, many cavities within the graft copolymer particles are found which correlate in size and frequency with the extent of stress whitening. Measurements of the density decrease in the stress whitened areas agree quantitatively with evaluations of the volume increase determined from the changes of the particles sizes in the electron micrographs. An analysis of the polymerization of the scattered light shows that shear bands or birefringence effects can be excluded as the cause of stress whitening. Based on the direct observation of the stress whitened areas and on the dependence of the scattering on wavelength and angle, the light scattering effects must be caused by the accumulation of the cavitiesin bandlike zones. These zones mark the otherwise invisible shear bands occurring on strong deformations of the PVC matrix. The initiation of the shear bands is facilitated by the incorporation of the graft copolymer particles which in this way enhance the impact strength of PVC.     

Phase Separation Time Measurement Using Optical Method for Solvent Characterization

Phase Separation Time is a characteristic parameter of a two-phase liquid-liquid extraction system essential to evaluate the solvent pair suitability in a solvent extraction process and the process throughput in a mixer-settler system. A novel light scattering technique to determine the phase separation time unambiguously has been developed for the first time at the Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam. The technique rests on the principle that dispersed mixture of two phases result in high scattering of an incident beam of light, and this scattering decreases as the dispersed phases coalesce. By monitoring the intensity of this scattered light at 90^o to the incident light, the “Phase Separation Time” can be deduced.     

A light scattering study of some solutions of triblock copolymers

Three samples of polystyrene-polybutadiene-polystyrene block copolymers have been studied by means of the light scattering technique in several solvents. The light scattering measurements indicate the degree of heterogeneity of the samples. Further measurements which were made on the least heterogeneous of the samples in a solvent closely matching the refractive index of the centre block suggest that the two types of polymer are largely separate. In this case the angular intensity variation of the light scattering can be interpreted in terms of the scattering obtained from a “dumb-bell” configuration.     

Design of thermochromic polymer blends containing low‐mass compounds

We investigated the light transmittance of an immiscible polymer blend comprising a copolymer of ethylene and vinyl acetate (EVA) and a terpolymer of vinyl butyral, vinyl alcohol, and vinyl acetate (PVB). Both EVA and PVB are used in the interlayers of laminated glass. We found that the transparency of the blend depends on the ambient temperature. This can be attributed to the difference in the temperature dependence of the refractive index between EVA and PVB. The blend has good transparency at room temperature because the difference between the refractive indices of its components is minimal. At high or low temperatures, however, the blend becomes opaque owing to light scattering. The addition of a plasticizer favorably affects the temperature range over which the blend exhibits high transparency, because the refractive index and its temperature dependence are affected by the plasticizer. We also evaluated the interphase transfer of a plasticizer between EVA and PVB at various temperatures. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45927.     

Effect of rigid particle size on the toughness of filled polypropylene

The role of rigid particle size in the deformation and fracture behavior of filled semicrystalline polymer was investigated with systems based on polypropylene (PP) and model rigid fillers [glass beads, Al(OH)₃]. The regularities of the influence of particle content and size on the microdeformation mechanisms and fracture toughness of the composites at low and high loading rates were found. The existence of the optimal particle size for fixed filler content promoting both maximum ultimate elongation of the composite at the tensile and maximum toughness at impact test was shown. The decrease of the toughening effect with both decreasing and increasing particle size regarding the optimal one was explained by dual role of particle size, correspondingly as either “adhesive” or “geometric” factors of fracture. The adhesive factor is due by the increase of debonding stress with the particle size decrease and the voiding difficulty resulting in the restriction of plastic flow. The geometric factor consists in the dramatic decrease of the composite strength at break if the void size exceeds the critical size of defect (for a given matrix) at which the crack initiation occurs. The analysis of the filled polymer toughness dependencies upon the particle size revealed that a capacity of rigid particles for the energy dissipation at the high loading rate depends on two factors: (i) ability of the dispersed particles to detach from matrix and to initiate the matrix local shear yielding at the vicinity of the voids and (ii) the size of the voids forming. Based on the findings it was concluded that the optimal minimal rigid particle size for the polymer toughening should answer the two main requirements: (i) to be smaller than the size of defect dangerous for polymer fracture and (ii) to have low debonding stress (essentially lower compared to the polymer matrix yield stress). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1917–1926, 2004     

Characterization of colloidal polymer particles through stability ratio measurements

We propose a general methodology for the estimation of the doublet formation rate constant (proportional to the stability ratio of primary particles) in colloidal dispersions from measurements obtained by common optical techniques, such as dynamic light scattering, static light scattering (nephelometry) or turbidimetry. In contrast to previous approaches relying on the initial slopes of the measured quantities, such as the mean hydrodynamic radius, scattered light intensity or turbidity, we introduce a transformation of the measurables to properly scaled quantities, which grow linearly in time with a slope proportional to the doublet formation rate. Analysis of systematic and random errors allows one to control the error in the estimated value of the aggregation rate. Using this approach, we measured the aggregation rate constant of colloidal polymer particles prepared by surfactant-free emulsion copolymerization of styrene and 2-hydroxyethyl methacrylate (HEMA). It was found that the stability ratio at constant ionic strength decreases with increasing dilution of the original polymer latex. This can be explained by the presence of non-reacted stabilizing species (most likely oxidized HEMA) that desorb from the particle surface upon latex dilution and thus diminish the repulsive interactions between particles. In order to check if the stability of latex particles is influenced by reversibly adsorbed species it is always necessary to perform aggregation experiments at various dilutions.     

A refractive-index and position-independent single-particle detector for large,nonabsorbing, spherical particles

We show that for spherical particles with real refractive index and diameters greater than ca. 10 microns, the differential scattering cross-section is only independent of the refractive index at angles near 37?±?5°. We built a device with a modified Gaussian incident beam profile so that the beam transit time of a particle passing through the beam can determine the true incident intensity for the scattering of the particle. By combining the modified Gaussian incident beam profile with detection of scattered light near 37?±?5°, we demonstrate a refractive-index independent measurement of single spherical particles as they pass through the beam.

Copyright © 2018 American Association for Aerosol Research