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Small Angle Light Scattering (small + angle_light_scattering)

Distribution by Scientific Domains

Polymers and Materials Science	100%

Selected Abstracts

On Different Approaches to Estimate the Mass Fractal Dimension of Coal Aggregates

PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 5 2005
Jimmy Y. H. Liao
Abstract Several methods to measure the structures of coal aggregates are compared. Loose and compact coal aggregates were generated through flocculation of ultrafine coal particles (mean volume diameter of 12,,m) under specific shearing conditions. Aggregate structure in terms of mass fractal dimension, Df, was determined using various methods; namely 2D and 3D image analysis, interpretation of intensity patterns from small angle light scattering, changes in aggregation state through light obscuration, and settling behavior. In this study, the measured values of Df ranged from 1.84,2.19 for coal aggregates with more open structures, and around 2.27,2.66 for the compact ones. All of these approaches could distinguish structural differences between aggregates, albeit with variation in Df values estimated by the different techniques. The discrepancy in the absolute values for fractal dimension is due to the different physical properties measured by each approach, depending on the assumptions used to infer Df from measurable parameters. In addition, image analysis and settling techniques are based on the examination of individual aggregates, such that a large number of data points are required to yield statistically representative estimations. Light scattering and obscuration measure the aggregates collectively to give average Df values of the particulate systems; consequently ignoring any structural variation between the aggregates, and leaving possible small contaminations undetected (e.g. by dust particles or air bubbles). Appropriate utilization of a particular method is thus largely determined by system properties and required data quality. [source]

Effect of thermomechanical history on the crystallization of poly(ether- block -amide)

POLYMER ENGINEERING & SCIENCE, Issue 12 2008
Bruno Tavernier
The quiescent and flow-induced crystallization of a poly(ether- block -amide) is studied by means of rheo-optical methods. Both optical microscopy and small angle light scattering have been used. The multiblock copolymer has a microphase-separated structure with an order,disorder transition at 180,185°C, as measured with rheometry and SAXS. The number of nuclei, spherulitic growth rates, and the characteristic time scale for crystallization are compared with that of a polyamide of similar molar mass. For the poly(ether- block -amide),containing a majority of amide segments,the growth rates of the spherulites during quiescent crystallization are similar for the block copolymer and the homopolymer, even if the spherulitic structures are not the same. When flow is applied, the two materials behave differently. The flow increased the nucleation density in the homopolymer but not in the block copolymer. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source]

Stretching induced phase transformations in melt extruded poly(vinylidene fluoride) cast films: Effect of cast roll temperature and speed

POLYMER ENGINEERING & SCIENCE, Issue 12 2007
Milind V. Mhalgi
Melt extruded poly(vinylidene fluoride) cast films were prepared at different cast roll temperatures and speeds to study the effect of casting temperature and preorientation of the melt on the ,- to ,-phase transformation in these films after uniaxial stretching. X-ray and fourier transform infrared spectroscopy were used to identify the crystalline phases. The unstretched films were characterized using small angle light scattering (SALS). The films were stretched to a stretch ratio of 4.2 and at 80°C. Birefringence of the films and the fraction of ,-phase [F(,)] formed after uniaxial stretching increased with stretch ratio. The films showed increased crystallinity after stretching. For the films prepared at different cast roll temperatures, there was little change in F(,) in the films having a cast roll temperature between 75 and 120°C, but for the film with a cast roll temperature of 130°C F(,) decreased considerably. For the films prepared at different cast roll speeds, the F(,) increased with stretch ratio as well as with cast roll speed for a fixed stretch ratio. The primary effect of changing both the parameters is a change in the average spherulitic radius (R), in the unstretched films measured using SALS. The F(,) obtained correlated well with R and lower spherulitic radii resulted in the higher conversion to the ,-phase. POLYM. ENG. SCI., 47:1992,2004, 2007. © 2007 Society of Plastics Engineers [source]

Influence of ionomeric compatibilizers on the morphology and properties of amorphous polyester/polyamide blends

POLYMER ENGINEERING & SCIENCE, Issue 9 2004
Gregory C. Gemeinhardt
The utilization of sulfonated polyester ionomers as minor-component compatibilizers in blends of an amorphous polyester and polyamide was investigated. The blends were prepared using twin-screw extrusion and compared to solution blends to investigate the effect of elevated temperatures and shear mixing on blend miscibility and/or phase behavior. The phase domain sizes of the solution blends with respect to ionomer content were studied using small angle light scattering (SALS) and phase contrast optical microscopy. The thermal and mechanical properties of the extruded blends were investigated using dynamic mechanical analysis (DMA) and tensile testing while the morphology was investigated using environmental scanning electron microscopy (ESEM). The interactions between the sulfonate group of the ionomer and the polyamide were characterized using FT-IR spectroscopy. Binary blends of the amorphous polyester and polyamide were immiscible with poor mechanical properties, while blends containing the polyester ionomer as a minor-component compatibilizer showed a significant reduction in the dispersed domain sizes and enhanced ultimate mechanical properties. The compatibilization mechanism is attributed to specific interactions between the sulfonate groups on the polyester ionomer and the amide groups of the polyamide. Polym. Eng. Sci. 44:1721,1731, 2004. © 2004 Society of Plastics Engineers. [source]