fulltext_011 - Chapter 12 Dynamic Light Scattering Contents...

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299 H.G. Merkus, Particle Size Measurements, DOI 10.1007/978-1-4020-9015-8_12,© Springer Science+Business Media B.V. 2009 12.1± ±Characteristics±of±Dynamic±Light±Scattering±Technique± Chapter 12 Dynamic Light Scattering Contents 12.1 Characteristics of Dynamic Light Scattering Technique . . . . . . . . . . . . . . . . . . . . . . 299 12.2 Principle of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300 12.3 Instrument Set-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301 12.4 Theoretical Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303 12.5 Practical Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306 12.5.1 Digital Correlation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306 12.5.2 Inversion of Correlation Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307 12.5.3 Sample and System Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309 12.5.4 Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310 12.6 Quality Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310 12.7 Qualification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312 12.8 Operational Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312 12.9 Limitations and Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313 12.10 Error Sources and Diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314 12.11 Practical Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314 12.12 Future Prospects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315 12.13 Definitions, Abbreviations and Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315 12.14 List of Instrument Manufacturers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317 Principle model-based calculation from dynamic changes of scat- tered light intensity at some angle Type of diameter intensity-based, hydrodynamic diameter Type of distribution -intensity-based size distribution -technique is best fit to identify modal size and width for narrow, lognormal PSD’s Measurement range 0.005–1 μm Calibration no; qualification recommended Sample types suspensions, emulsions Sample size μg to mg quantities Measurement time about 1 min Repeatability D mean about 2–5% relative Bias D mean smaller than 2% relative Resolution 30% relative Sensitivity about 10% (v/v) Traceability only indirectly Ease of operation good
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300 12 Dynamic Light Scattering ±12.2± ±Principle±of±Operation± The technique is known by different names. Dynamic light scattering (DLS) is the name that covers different techniques for measurement of particle size from the dynamic changes of the scattered light intensity. Photon correlation spectroscopy (PCS) is at present the most widely used name. It relates to the correlation technique that is most frequently applied in instruments. Quasi-elastic light scattering (QELS) was used as a name often in the past. This term relates to the type of interaction between particles and light. The term Diffusing Wave Spectroscopy is often used for applications in concentrated dispersions, where multiple scattering leads to a diffusive transport of light. In the DLS technique, the intensity of the scattered light by an ensemble of particles is measured at a given angle as a function of time. The Brownian motion of the dispersed particles determines the rate of change of the scattered light intensity. The temporal intensity changes are converted to a mean trans- lational diffusion coefficient (or a set of diffusion coefficients). Fast intensity changes are related to a rapid decay of the correlation function and a large Costs -investment medium to high, about 30–60 k -labor small Influence of shape yes Standardization ISO standard available Remarks -very low particulate concentration required for abso- lute measurement; relative size values can be obtained at increased concentration -many liquids allowed for dispersion In-/on-line capability - only if movement of dispersion is insignificant -
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This note was uploaded on 05/06/2010 for the course MECH. 28197 taught by Professor Dr.shafii during the Spring '10 term at Sharif University of Technology.

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fulltext_011 - Chapter 12 Dynamic Light Scattering Contents...

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