Other light scattering methods

A simple light scattering photometer was designed, to measure the angular distribution of intensity of scattered, polarized, He/Ne light, by micron and sub-micron particles [186]. The photometer used an ellipsoidal reflector and simple optical components to collect the scattered light and focus it on a 512 element photodiode array. 

The intensity ratio method is based on measurements of light scattered at two angles and applies to the size range 0.1 to 10 pm [187]. Due to the possibility of large errors [188] the method has found little application. 

Using Scanning Flow Cytometry the size distribution of submicron spherical particles is determined from the scattered light intensity ratios at two angles. In one example the ratio at 67° and 15° was used to determine sizes between 1 and 15pm at a flow rate of 500 particles per second [189]. This was extended to 0.5 to 14 pm using a parametric solution based on analytical approximating equations [190]. 

The ratio of the polarized light intensity scattered from two different coaxial beams illuminating a particle can be used to determine particle size. Azzizy and Hess [191] used two coaxial beams of different wavelengths at 30° from the forward axis polarized in different directions. The ratio of these two parameters gives a unique curve that is a function only of particle size. They found errors of a similar magnitude to those found with intensity ratio methods. 

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Often in hyperbranched polymers obtained via SCVP, it is not possible to determine the DB directly via NMR analysis. Therefore, other methods, for example, viscosity measurements and light-scattering methods have to be used to confirm the compact structure of a hyperbranched polymer. Such characterizations of hyperbranched (meth)acrylates will be discussed in the next section. 

The light scattering method is considerably more involved (theoretically and practically too) than the other methods. It can be used at extremely low concentrations of solution with sufficient accuracy. A wide range of molar mass (from a few hundreds to a few lakhs) can be determined and it is one of the most reliable methods for determining the shapes of large molecules. 

On the other hand, a liquid/liquid interface is fluctuating thermally in the time scale of tens of picoseconds, and this induces thermal capillary waves as discussed above. Thermal capillary waves at a flat liquid/liquid interface have been studied by laser light-scattering methods, and the wavelength of the capillary wave (2) has been reported to be A 102 /im [29-31], A large... 

Light scattering methods (often in combination with other experimental methods) are widely used for the investigation of complex surfactant systems such as mixed micelles, " block... 

Beside the very frequently used methods of dynamic surface and interfacial tension measurements, adsorption kinetics processes at liquid interfaces can also be studied by other methods, such as dynamic surface potentials, ellipsometry and other light scattering and reflection methods, X-ray techniques, neutron scattering, radiotracer techniques. These methods yield more or less relative information on the change of adsorption with time at different time resolutions. 

Light scattering measurements can also be used to determine the molecular weight (M2) of solute molecules as well as interactional (second and third virial coefficients) and structural parameters (radius of gyration) [60, 61]. The reader is referred to Chapter 18 for more information on light scattering methods. The dependence of A2 and Rj) on M have been the subject of many research studies in polymer solution thermodynamics [29, 62]. Many other experimental techniques can been used to determine these and other related parameters [28, 35, 63]. 

The surface light scattering method has been used to show that the low interfaciai tensions in the Winsor I and II systems (O/W microemulsion in equilibrium with excess oil and W/O microemulsion in equilibrium with excess water, respectively) are due to the large surface pressure of the surfactant monolayer coating the interface, which almost balances the bare oil/water interfaciai tension [36,37]. Schulman and Montagne [38] proposed early that the low interfaciai tensions in microemulsion systems should be associated with these large surface pressures tt, i.e., 7 = 70 - tc 0. In other models, the origin of the low interfaciai tensions was attributed to the vicinity of critical points [39,40]. 

In this chapter we will review the light scattering method of photon correlation spectroscopy (E CS) for the sizing of dispersed suspensions of submicrometer particles of interest in pharmacology. These particles may be macromolecules of varying types including liposomes and other laminar vesicles, micelles, and droplets in microemulsions. 

Light Scattering Methods Raman Spectroscopy and other Processes... 

CHS LIGHT SCATTERING METHODS RAMAN SPECTROSCOPY AND OTHER PROCESSES... 

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