Light Scattering Device

Scattering techniques are non-destructive methods to study structure and dynamics in colloidal systems. A major challenge in light scattering is the investigation of turbid or highly concentrated samples, where multiple-scattering of the primary beam may lead to results that are wrong by orders of magnitude and hence to misinterpretation of the data. To avoid multiple-scattering we use a 3D cross correlation set up. In contrast to the common autocorrelation, the 3D cross correlation uses two simultaneous light scattering experiments, performed at the same time and the same scattering vector. For this purpose the primary beam passes a beam splitter before being focused into the sample. The measured intensities from both experiments are correlated with each other, thus only single-scattering events contribute to the signal. Besides dynamic measurements, the LS instruments set up further allows static light scattering experiments on strongly scattering samples.

Basic features:

• Angular range 15°-150°
• Particle characterization down to 1nm
• Determination of molecular weight
• Automated data treatment using CONTIN (inverse Laplace transformation based on Rayleigh Debye Gans spheres) and cumulant analysis
• Temperature control unit
• Non-ergodic sample characterization possible

The second part of the light scattering work bench is a diffusing wave spectrometer. The special feature of this technique is the detection of viscoelastic properties of a colloidal sample without applying mechanical shear forces. Storage and loss moduli can be detected in a huge frequency range within short time applying only small sample volumes. In the case of diffusing wave spectrometry turbid samples are desired. Intensity fluctuations from the multiply scattered primary laser beam are detected and the mean square displacement of the scattering particles is obtained to which the principle theories underlying micro-rheology can be applied.

Two operating modes are possible, transmission mode and backscattering mode. Depending on the sample, tracer particles can be added allowing as well the measurement of transparent samples.


Basic features:

• Two-cell technology allows non-ergodic sample characterization
• Measurement of storage and loss moduli within minutes at frequencies up to 10⁷ Hz
• Particle sizing in highly turbid samples
• Automated control and data treatment
• Temperature control unit
• Different cell holders allowing optical path-length variation between 1-10mm