QELS = quasi-elastic scattering

QELS = quasi-elastic (light) scattering see electromagnetic radiation, scattering quadrupole moment 1.4.19, 1.5.42... 

Samples were taken at different reaction times and immersed in a water bath to quench the reaction. The following tests were performed size measurement using QELS (quasi-elastic light scattering. Coulter Model N4 SD) and yield measurement. For QELS, the samples were diluted with distilled and deionized water and the run time was 400 s. For the yield measurement, the sample was centrifuged at 12,000 rpm for at least IS min, then the mass of the dried solid was measured. 

Photon Correlation Spectroscopy. Photon correlation spectroscopy (pcs), also commonly referred to as quasi-elastic light scattering (qels) or dynamic light scattering (dls), is a technique in which the size of submicrometer particles dispersed in a Hquid medium is deduced from the random movement caused by Brownian diffusion motion. This technique has been used for a wide variety of materials (60—62). 

The technique is alternatively called photon correlation spectroscopy (PCS) or quasi-elastic light scattering (QELS). 

Effect of Radiation Dose on Micellar Properties. Figure 1 shows the concentration dependence of the micellar diffusion coefficient at 40° as determined by quasi-elastic light scattering (QELS) for solutions subjected to radiation doses of up to 4.56 Mrad. Limiting diffusion coefficients, D0>were obtained by extrapolation of data for dilute solutions (<0.05%) to zero concentration, the critical micelle concentration (CMC) being negligibly low for this poloxamer ( 1 ). 

Many excellent introductions to quasi-elastic light scattering can be found in the literature describing the theory and experimental technique (e.g. 3-6). The use of QELS to determine particle size is based on the measurement, via the autocorrelation of the time dependence of the scattered light, of the diffusion coefficients of suspended particles undergoing Brownian motion. The measured autocorrelation function, G<2>(t), is given by... 

An alternate approach for determining particle density involves fraction collection followed by the application of quasi-elastic light scattering (QEL) to the fraction (19). The QEL technique is particularly effective in providing a mean particle diameter d for narrow particle distributions. With this d and the X obtained from V (the volume at which the fraction was collected), Ap can be calculated directly from Equation 3. 

---