Laser light diffraction

The surface mean diameter is the diameter of a sphere of the same surface area-to-volume ratio as the actual particle, which is usually not a perfect sphere. The surface mean diameter, which is sometimes referred to as the Sauter mean diameter, is the most useful particle size correlation, because hydrodynamic forces in the fluid bed act on the outside surface of the particle. The surface mean diameter is directly obtained from automated laser light diffraction devices, which are commonly used to measure particle sizes from 0.5 to 600 p.m. X-ray diffraction is commonly used to measure smaller particles (see Size TffiASURETffiNT OF PARTICLES). 

The particle size analyzer, based on laser light diffraction, consists of a laser source, beam expander, collector lens, and detector (Fig. ] 3.45). The detector contains light diodes arranged to form a radial diode-array detector. The particle sample to be measured can be blown across the laser beam (dry sample), or it can be circulated via a measurement cell in a liquid suspension. In the latter case, the beam is direaed through the transparent cell. 

The vesicle size is an important parameter not only for in-process control but particularly in quality assurance, because the physical stability of the vesicle dispersion depends on particle size and particle size distribution. An appropriate and particularly quick method is laser light scattering or diffraction. Laser light diffraction can be applied to particles > 1 pm and refers to the proportionality between the intensity of diffraction and the square of the particle diameter according to the diffraction theory of Fraunhofer. 

Frake et al. compared various chemometric approaches to the determination of the median particle size in lactose monohydrate with calibration models constrncted by MLR, PLS, PCR or ANNs. Overall, the ensuing models allowed mean particle sizes over the range 20-110/tm to be determined with an error less than 5 pm, which is comparable to that of the laser light diffraction method nsed as reference. Predictive ability was similar for models based on absorbance and second-derivative spectra this confirms that spectral treatments do not suppress the scattering component arising from differences in particle size. 

The characterization of emulsions by particle size distribution analysis has been facilitated in recent years by a range of new instruments. Most of these instruments employ laser light diffraction principles, and have replaced older spectrophotometric methods. 

Particle size is an important property with respect to the sensory quality of chocolate, and in chocolate manufacture. It can be measured using laser light diffraction spectrophotometry (see Section 22.2.11.2), and by a variety of other means such as micrometry, microscopy, wet sieve fractionation, sedimentation and Coulter counting (Minifie, 1999). 

Table 2 compares the estimated Mayer Stowe median particle size D with the corresponding median particle size diameter D50 measured by laser light diffraction... 

Kanerva H, Kiesvaara J, Muttonen E, Yliruusi J. Use of laser light diffraction in determining the size distribution of different shaped particles. Pharm Ind 1993 55 849 - 853. 

Fig. 1 Single cell elasticity measurements with microindentation technique. (A) AFM allows both live cell imaging and mechanical testing (e.g., microindentation) in near physiological conditions. The AFM tip attached to a cantilever descents slowly to a surface and causes an indentation. The depth of indentation is detected by laser light diffraction pattern. (B) Typical force-distance curves are obtained for hard and soft surfaces and usually analyzed with the classical Hertz model that relates the applied force to the indentation depth.

Coulter LS Series particle size distribution analyser Laser light diffraction 0.1-810 pm 60 Particle sizing... 

Figure 8.16 Typical result of a particle size distribution obtained by laser light diffraction.

Figure 8.17 Comparison of particle size distribution measurements by laser light diffraction and sieve analysis. In part (a), it can be seen that the overall agreement is ve7 good. Part (b) shows the result of sieving of a ve7...

For spherical particles, the measured particle size distribution by laser light diffraction and sieving may be very similar (Figure 8.17). 

For rodhke particles, sieving essentially determines the diameter of the rod, whereas laser light diffraction determines the diameter of a sphere with same volume as the rod. Therefore, the result obtained by sieving will be smaller than that obtained by laser light diffraction. The opposite applies for platelike particles, where sieving measures the diameter of the plate. 

The XY model gives helical structures with a very short pitch consisting of several layers. Because of such an ultrashort pitch, the system should appear to be optically uniaxial with the optic axis along the layer normal, and to exhibit negligible circular dichroism (CD) and optical rotatory power (ORP). However, macroscopic helices have been observed experimentally not only in SmC [74] but also in the subphases. Actually, Miyachi et al. [75], [76] observed laser light diffraction in the SmCy and AF phases of (R)-MHPBC. In this respect, the XY model, particularly the clock model, is not a realistic model for various subphases possessing macroscopic helices. Future studies are necessary to fully understand the appearance of various subphases. 

X-ray and neutron scattering are suited to determine the size and anisometry of micelles. This gives useful information because there is an influence of these properties on the magnitude of the phase chirality of lyotropics. If the pitch of chiral phases is in the range of a few pm or below, it can be measured by means of laser light diffraction. Cano preparations have not been used for pitch determination. 

Figure 5.11 Particle size distribution measured with static laser light diffraction of PMMA particles filled with SiOi nanoparticles and TEM picture of the core-shell nanoparticles.

Typical initial parameters for two standard experiments are listed in Table 1. The masses m of sodium silicate, respectively, sulphuric acid are referred to the total mass of water in the mixed solution. On the basis of these parameters, the temperature d, ionic strength / (addition of NaCl and Na2S04> and the energy dissipation e due to the stirrer speed n, may be varied systematically. After gelation, i.e. t > tg, samples of the reactor content are taken with a syringe and the fragment size distribution is determined with laser light diffraction Mastersizer S, Malvern Instruments). 

Brown, D. I, Felton, P. G., Direct Measurement of Concentration and Size for Particles of Different Shapes using Laser Light Diffraction, Ghent Eng. Res. Des., 1985, 63, 125-132. 

Kouzelis, D., Candel, S. M., Esposito, E., Zikikout, S., Particle Sizing by Laser Light Diffraction Improvements in Optics and Algorithms,Part Charact, 1987,4, 151-156. Bayvel, L. P., Knight, J., Roberston, G., Alternative Model-Independent Inversion Programme for Malvern Particle Sizer, Part Charact, 1987,4,49-53. 

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