Dynamic light scattering particle size analysis

Methods for analysis of the particle size distribution in the aerosol cloud include techniques such as time of flight measurement (TOE), inertial impaction and laser diffraction. Dynamic light scattering (photon correlation spectroscopy) is confined to particles (in suspension) in the submicron range. In addition to the size distribution, the particle velocity distribution can be measured with the Phase Doppler technique. 

It is our objective in this chapter to outline the basic concepts that are behind sedimentation and diffusion. As we see in this chapter, gravitational and centrifugal sedimentation are frequently used for particle-size analysis as well as for obtaining measures of solvation and shapes of particles. Diffusion plays a much more prevalent role in numerous aspects of colloid science and is also used in particle-size analysis, as we see in Chapter 5 when we discuss dynamic light scattering. The equilibrium between centrifugation and diffusion is particularly important in analytical and preparative ultracentrifuges. 

For colloidal semiconductor systems, Albery et al. observed good agreement between the value of the radial dispersion obtained from dynamic light scattering and the value found from application of the above kinetic analysis to flash photolysis experiments [144], It should be remembered that this disperse kinetics model can only be applied to the decay of heterogeneous species under unimolecular or pseudo-first order conditions and that for colloidal semiconductors it may only be applied to dispersions whose particle radii conform to equation (37), i.e., a log normal distribution. However, other authors [145] have recently refined the model so that assumptions about the particle size distribution may be avoided in the kinetic data analysis. 

One of the practical applications of dynamic light scattering involves the determination of particle sizes in media dispersed as dilute suspensions in a liquid phase. This aspect of dynamic light scattering is the focus here. Analysis of the scattering data will yield the translational diffusion constant D for a dilute aqueous suspension of polystyrene spheres, and this is directly related to the radius of the spheres. In addition, scattering will be studied from dilute skim milk, which reveals that a distribution of particle sizes exists for this system. 

Nicomp380/DLS Submicron particle sizer uses dynamic light scattering with a size range of 0.003 to 5 pm with unique modular options. An Autodilution unit that eliminates the need for manual dilution of concentrated samples [307] an Auto-sampler that permits automatic batch analysis of as many as 76 samples high-power laser diodes, multi-angle options and zeta-potential accessory. 

Dynamic light scattering (DLS) (model B1-9000AT, Brookhaven Instrnments Corp., Holtsville, NY) was nsed to estimate the particle size and particle size distribution of the resulting BT powders. The samples were dilated with deionized water and ultrasonicated for 15 min jnst before the size analysis. Room temperature XRD (Scintag PAD V using CnKa with X = 0.15406 nm) was nsed for crystalline phase identification and determination of the crystallite size of the powder. The crystallite size of BaTiOj powders was calcnlated by the Scherrer eqnation ... 

Sol-gel silica particles of four different sizes, viz. 0.2 pm, 0.5 pm, 1.0 pm and 1.5 pm were obtained from Geltech Corporation. Particle size analysis on the slurries was carried out using a Honeywell Microtrac UPA 150 particle size analyzer, which utilizes the dynamic light scattering technique. In addition. Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) was also used for determining particle size and shape. 

Another technique (Fig. 21-13) utilizes an optical system which minimizes the optical path into and out of the sample, including the use of backscatter optics, a moving cell assembly, or setups with the maximum incident beam intensity located at the interface of the suspension to the optical window (Trainer, Freud, and Weiss, Pittsburg Conference, Analytical and Applied Spectroscopy, Symp. Particle Size Analysis, March 1990 upcoming ISO 22412, Particle Size Analysis— Dynamic Light Scattering). 

The microstructure and particle morphology (size, shape, and surface roughness) of the colloids were studied with 13C and 29Si NMR spectroscopy, elemental analysis, transmission electron microscopy, and static and dynamic light scattering. 

DLS (dynamic light scattering)—in dynamic light scattering laser light is scattered by the nanoparticles. Due to the Brownian motion of the particles, a time-dependent fluctuation is imparted to the scattered light intensity. Analysis of the signal intensity yields information about the diffusional motion of the particles, which is in turn related to the hydrodynamic size via the Stoke-Einstein equation. 

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