Autocorrelation function dynamic light scattering

The intensity and the autocorrelation function of light scattered by a microemulsion have been investigated for the water in oil type microemulsions. We studied two mixtures water-SDS-cyclohexane-pentanol and water-SDS-toluene-butanol. We obtain information about droplet size (radius of the aqueous core, hydro-dynamic radius) and about interaction forces between the droplets (from osmotic compressibility and diffusion coefficient data). 

In contrast, in dynamic light scattering (DLS) the temporal variation of the intensity is measured and is represented usually through what is known as the intensity autocorrelation function. The diffusion coefficients of the particles, particle size, and size distribution can be deduced from such measurements. There are many variations of dynamic light scattering, and... 

FIG. 5.16 Schematic illustration of intensity measurement and the corresponding autocorrelation function in dynamic light scattering (a) variation of the intensity of the scattered light with time (b) the variation of the autocorrelation function C(s,td) with the delay time td. 

Dynamic Light Scattering. The measured single clipped photoelectron count autocorrelation function for the self-beating experiment has the form (5)... 

Dynamic light scattering measurements were performed with a Malvern photon correlation system eqxiipped with a krypton ion laser KR 165-11 from Spectra Physics (1 =647.1 nm). The intensity time correlation function (TCP) was recorded by a Malvern autocorrelator. The electric field TCP g,(t) normalized to the base line of the intensity TCP, and its first cumulant F = -Slng (t)/3t at time to were calculated as usual ( )by an on-line computer where 80 cheinnels of a total of 96 chemnels were used for the recording of the TCP, and the leist 12 channels, shifted by 164 seusple times, were used for the detection of the beise line. 

Dynamic light scattering allows measurement of the translational diffusion coefficient A of particles. For noninteracting particles, the first-order autocorrelation function g r) is directly proportional to A- Polydisperse systems are analyzed using the method of cumulants, in which a distribution of exponential terms C(r) is assumed ... 

FIGURE 8.22 Hydrodynamic radius of PPy-DBSA in chloroform containing different amounts of extra DBSA at 25°C, where the concentration of PPy-DBSA is 0.01 g/dL The inset shows autocorrelation functions obtained from the dynamic light scattering analysis. (From Song, K.T., Synthesis of electrically conducting soluble polypyrrole and its characterization. Ph.D. thesis, 2000. With permission.)... 

The Dynamic Light Scattering (DLS) technique was used to measure radii of the PS latex spheres with and without adsorbed polymer brushes. We could then deduce the polymer brush hydrodynamic layer thickness by taking the difference of the radii. DLS measures the intensity autocorrelation as a function of delay time, which gives information on the diffusion constant of particles in a dilute solution. The translational diffusion coefficient, D, is related to the solution temperature T, particle radius r, and solvent viscosity ri by the Stokes-Einstein relation ... 

The size distribution of the liposomes is determined by dynamic light scattering (DLS) with a Dynapro apparatus (http //www.wyatt.com). DLS is a hydrodynamic method by which one determines the rate of diffusion of particles through the solvent. The hydrodynamic radius is defined as the radius of a theoretical hard sphere that diffuses with the same speed as the particle under examination. The measurement is performed at 25° and requires about 2 /ul of the extruded liposome suspension diluted in 18 /ul of liposome buffer (final lipid concentration in the range of 0.1 roM). Ten autocorrelation functions are sequentially measured, from which the size distribution of the liposome is determined using the Dynamics v5 software from Dynapro. A complete measurement takes a few minutes. Figure lA shows typical size distributions of extruded liposomes as determined by DLS. Figure IB shows how the actual hydrodynamic radius of the liposomes varies with the pore size of the polycarbonate filter. 

Figure 3.1. Dynamic light scattering measurement system. The pulse-amphfier discriminator converts the analog signal of the photodetector, I t), into a digital signal, which is further converted by the autocorrelator into the autocorrelation function of the signal.

The hydrodynamic radius of colloidal particles can be obtained from dynamic light scattering (DLS), also known as photon correlation spectroscopy (PCS). Here, the temporal fluctuations of scattered light intensity are measured to provide the autocorrelation function, analysis of which provides the translational diffusion coefficient. Then the Stokes-Einstein equation (Eq. 1.9) is used to determine a hydrodynamic radius. This method is described further in Section 1.9.2. 

The dynamics of the collective excitations can be determined conveniently by photon autocorrelation spectroscopy, which is also called self-beating, time-resolved Rayleigh or quasi-elastic light scattering spectroscopy [29]. Here the time autocorrelation function of the scattered light intensity G (t) is measured, which, in the heterodyne detection regime, is given by ... 

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