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Dynamic light scattering in turbid nonergodic media
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Image of FIG. 1.
FIG. 1.

The sample cell for turbid samples with variable cell thickness.

Image of FIG. 2.
FIG. 2.

The optical path of the modified 3D-DLS. Implementing the polarization filters leads to a decoupling of the two DLS experiments, and thus to an improved intercept of up to 0.6 instead of 0.15.

Image of FIG. 3.
FIG. 3.

The cell orientation. The scattering volume is always in the cell center.

Image of FIG. 4.
FIG. 4.

The 3D-echo-DLS-flat-cell-light scattering instrument. The arrow marks the position of the thermo-jacket and the echo-DLS inset.

Image of FIG. 5.
FIG. 5.

The realization of the echo DLS. The underlying mechanics consists in a planetary gear, a worm drive, and two bearings (one in front, the other behind the flat cell position).

Image of FIG. 6.
FIG. 6.

Comparison of DLS results, (radius (+), transmissions (red dots), and intercept (x) measured at a scattering angle of 40° as a function of the weight fractions wf from different experiments: (a) standard DLS, (b) FCLSI-DLS, (c) 3D-DLS, open symbols (radius and intercept △): data taken at the edge of a square cell, (d) FCLSI- and 3D-FCLSI-DLS: radius and intercept .

Image of FIG. 7.
FIG. 7.

The angular range of the 3D-FCLSI-DLS. The hydrodynamic radius and the intercept are measurable between and 50°. (The scattering vector is measured in the sample).

Image of FIG. 8.
FIG. 8.

An echo-DLS measurement. (a) Raw data where the vertical lines represent the echoes. (b) A scaled up echo. (c) The area-corrected correlation curve (-◼-) and the normalized echo width (solid line). (d) A divergent echo width.

Image of FIG. 9.
FIG. 9.

A sketch of the measurement scenario where the speckles are symbolized by the small filled circles. All speckles that lie on a circle at the end of the cone are detected. The circumference of this circle depends on the scattering angle.

Image of FIG. 10.
FIG. 10.

Testing of the echo-DLS performance on: (a) ground glass (the small fluctuations are caused by statistical noise. The statistics is worse in the case of ground glass because of fewer scatterers), (b) latex spheres in glycerol (the results are compared to the brute force method; the horizontal and vertical rotation positions are used for the echo DLS), and (c) PMMA particles (diameter of and volume fraction of 57%). The results are compared to the multispeckle method. In this case the data were not renormalized. In general renormalization must be considered to match correlation curves measured with different techniques.

Image of FIG. 11.
FIG. 11.

The influence of the orientation of the rotation axis. If the nonergodic sample is rotated vertically (rotation axis is horizontal) the dynamical decay is faster (solid line) due to the gravitational influence.

Image of FIG. 12.
FIG. 12.

The confinement effect: (a) a simulation taken from Ref. 25 showing the dependence of the dynamics as a function of the distance from the wall. The origin is in the cell wall and the cell has a thickness of 15 particle diameters. The dotted line corresponds to the bulk dynamics and the thick solid line, that shows a linearly decaying tail, is the dynamics averaged over the cell thickness is the intermediate scattering function. (b) An experimental result measured with a flat cell and the echo DLS. The cell thickness was and the particle diameter was .


Generic image for table
Table I.

Maximum weight fractions for different DLS methods. (a) 3D-DLS using a cylindrical cell. (b) 3D-DLS performed at the edge of a square cell.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Dynamic light scattering in turbid nonergodic media