Particle model, calculation theoretical scattered

Figure 3. Two particle models used to calculate the theoretical scattered intensity. (A) = the discoid (B) = the closed lamella (o) water molecule ( ) s oxyethylene chain ...

Electrophoretic light scattering (ELS) is commonly used to measure v. The electrophoretic mobility /r can be calculated from v and the known value of E according to Eq. (I). Theoretical models [ I.7-I0] that describe colloidal electrostatics and hydrodynamics can then be used to relate the measured values of n to particle electrical characteristics including surface charge density and surface electric potential. Because /r depends on the surface electrostatic properties but not particle bulk properties, ELS can characterize surface electrostatic properties exclusively for a wide range of colloidal materials. 

The detailed results of the photochemical models are dependent on the adopted UV radiation field as well as on the photodissociation and photoionisation cross-sections, which in principle can be obtained by laboratory or theoretical studies, and on the nature of the dust particles for which the chemical composition, size and hence optical properties are poorly known. In the absence of definitive information, detailed models of the photochemistry have relied on some rather simplistic approaches to the radiative transfer of UV photons through the envelope. Nejad and Millar (1987,1988) have used the approach developed by Jura and Morris (1981) which assumes that the dust grains absorb but do not scatter and leads to a numerically simple equation for the intensity of UV radiation at any point in the envelope. On the other hand, Glassgold and co-workers have used a formalism devised by Gerola and Glassgold (1978) in which the scale-length, dp for photodissociation of any species is used to diminish the intensity incident on the CSE, that is, the intensity is reduced by a quantity exp(-d(/r). These authors have also included the effects of both continuum and line self-shielding in their calculations. 

In the limit ofL/Lp 1, eqn [158] becomes R = (2Lp) (L/2Lp)/6 for a Gaussian chain, while in the limit of L/fp< 1, R =L I12 for a thin rod. Rh can also be theoretically calculated for the wormlike chain. Static and dynamic light scattering experiments demonstrate that the model can successfidly describe stiff polymer molecules to extraa their characteristic quantities. Many calculations have been reported to theoretically evaluate Rg and Rh for rigid particles of various shapes. Table 2 lists Pig], Rg, and Rh for some rigid particles with a weU-defined shape. For a spherical uniform particle of radius R, we calculate Rg by eqn [30] as... 

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