Application Notes DLS/SLS

 
 
 

Image is the link to the page:Multi-angle DLS: Characterizing the Size of an Highly Polydisperse Model System

 

Traditional DLS instruments perform measurements at one or two scattering angles. While this approach is sufficient in case of monodisperse samples, it does not provide sufficient results when certain degree of polydispersity occurs. This is due to the fact that particles of different sizes scatter light differently at different angles. Therefore, measurements at several angles are required to accurately characterize polydisperse  samples. Herein, we demonstrate multi-angle DLS measurements as an elegant tool for characterization of polydisperse samples.

 
 
 

turbidity limits, DLS, diluted, 3D cross-correlation, technology, multiply-scattered light

 

Standard DLS provides accurate particle sizes only in case of strongly diluted samples. As concentration of colloid increases, the higher contribution from multiply-scattered light leads to errors in the measurement. One way to overcome this problem is to use the 3D cross-correlation technology enabling the measurement of even highly scattering samples by extracting only the singly scattered light from the detected signal.

 
 
 

colloidal suspensions, sls, dls, light scattering, cross-correlation, form factor,

 

SLS measurements, just as DLS measurements, are strongly effected by multiple light scattering. The detection of minima in form factor determination is severely affected for example. Here we demonstrate how DLS cross-correlation measurements can be combined with SLS to recover the true particle form factor by extracting only the single-scattering information.

 
 
 

particle sizing, scattering, DLS, light, 3D cross-correlation, autocorrelation function

 

In DLS experiments the particle size is calculated from the intensity fluctuations of the scattered light. Traditional DLS is based on the computation of the auto correlation function. This however, only works for highly diluted systems. This is specifically dangerous, since the magnitude of the error caused by multiple scattering cannot be deducted from the auto correlation function. So the user is often not aware of the problem. Here we shown a broad range of measurements on different concentrations and compare the results obtained with auto correlation to those obtained with the 3D cross-correlation technique to illustrate this problem.

 
 
 

dilute, concentrated, microgel, suspension, temperature, shrinking, swelling, temperature control

 

Microgels such as PNIPAM are intelligent materials that can respond to environmental changes. In our example the response is a variation of the particle size (shrinking and swelling) depending on the temperature of the surrounding environment. We use dynamic and static light scattering to study this phenomenon.

 
 
 

microgels, temperature, PNIPAM-BIS, DLS, 3D cross-correlation, concentrated samples, shrinking

 

Temperature dependent phase behavior of PNIPAM-BIS microgels can be studied with both DLS as well as SLS. Increasing the temperature results in particle shrinking which is simultaneously reflected in measured decreased hydrodynamic radii and radii of gyration. The comparison of the two radii gives additional insight on the structure of the microgel.

 
 
 

Zimm Plot facilitates SLS data treatment obtained with LS SPectrometer

 

Macromolecular systems, such as polymers, aggregates of surfactants or proteins, can be studied by performing SLS measuremements. Zimm Plot provides an convinient way to extract an information about the molecular weight, radius of gyration, and second viral coefficient.