Light scattering INDEX

Porogen Refractive Index Light Scattering Index Pore Size Range fnm) Dielectric Constant... 

Equations (10.17) and (10.18) show that both the relative dielectric constant and the refractive index of a substance are measurable properties of matter that quantify the interaction between matter and electric fields of whatever origin. The polarizability is the molecular parameter which is pertinent to this interaction. We shall see in the next section that a also plays an important role in the theory of light scattering. The following example illustrates the use of Eq. (10.17) to evaluate a and considers one aspect of the applicability of this quantity to light scattering. 

Suspended particles are the most important factor in visibility reduction. In most instances, the visual quality of air is controlled by partide scattering and is characterized by the extinction coeffident The size of particles plays a crucial role in their interaction with light. Other factors are the refractive index and shape of the particles, although their effect is harder to measure and is less well understood. If we could establish these properties, we could calculate the amount of light scattering and absorption. Alternatively, the extinction coeffident associated with an aerosol can be measured directly. 

There are a number of applieations such as bottle and film where tough materials of high elarity are desired. The advent of MBS material has been a significant advance to meet the requirements. It has been found possible here to produce an additive with sufficiently different solubility parameters from the PVC for it to exist in the disperse phase but with a very similar refractive index to the PVC so that light scattering at the interface between the two phases is at a minimum. However, owing to differences in the formulation of PVC compounds, a particular MBS modifier may not have exactly the same refractive index as the PVC eompound. 

Select the detector. To acquire molecular weight distribution data, use a general detector such as a refractive index detector. To acquire structural or compositional information, employ a more selective detector such as an ultraviolet (UV) or infrared (IR) detector. Viscometric and light-scattering detectors facilitate more accurate molecular weight measurement when appropriate standards are not available. 

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