Dynamic & Static Light Scattering

 

Model: BI-200SM system

Manufacture: Brookhaven Instruments Company (BIC)

 

Light Scattering


Light Scattering occurs when polarizable particles in a sample are bathed in the oscillating electric field of a beam of light. The varying field induces oscillating dipoles in the particles and these radiate light in all directions. This important and universal phenomena is the basis for explaining why the sky is blue, why fog and emulsions are opaque and other observations. It has been utilized in many areas of science to determine particle size, molecular weight, shape, diffusion coefficients etc.


With our D/SLS system this rich field of exploration is open to you for studies of both Static Light Scattering (SLS) and Dynamic Light Scattering (DLS). In the SLS mode time-averaged intensity measurements are made - at either fixed or variable angles - in the range from 80 to 1550 and analyzed with software provided for the methods of Zimm, Berry, Debye, Guinier, Kratky etc. Such evaluations using measured angular or concentration dependencies of the intensity of the scattered light provide key information for those interested in the topics below.

      

 

 

The field of DLS measurements is at least as rich as that of SLS. In this method the dynamics of the scattered light are determined and analyzed. The short-term intensity fluctuations (dynamics) of the scattered light arise from the fact that the scattering particles are undergoing rapid thermal motions. These movements are called Brownian motion and they cause short term fluctuations in the intensity of the scattered light. Various terms have been used for this phenomenon. These are Dynamic Light Scattering (DLS), Photon Correlation Spectroscopy (PCS) and Quasi-elastic Light Scattering (QELS), We will adhere to DLS. To uncover the key parameters which describe the diffusive motions a Digital Autocorrelator is used to determine the autocorrelation function (ACF).

 

The new BI-9000AT Digital Correlator is an advanced and extremely versatile digital photon correlator and counter designed for use in static (SLS) and dynamic (DLS) light scattering. It is supplied in the form of a single PCI or ISA compatible card with control software for installation in a PC.

The Bl-200SM Research Goniometer System provides access to all of the above studies with an automatic, modular and versatile  system. It is a precision instrument designed for exacting scattering measurements. Based on a special turntable with precision ball bearings and stepping motor, the Bl-200SM's modern design and quality construction guarantee precise measurements due to the wobble-free movement of the detector. Field proven in hundreds of laboratories, the Bl-200SM provides the capability of both total intensity (SLS) and photon correlation DLS measurements. It is ideal for macro-molecular studies and submicron particle sizing.

The BI-200SM's modularity simplifies system expansion. Featuring a standard optical rail, the BI-200SM can be used with neutral density filters, a polarizer, an analyzer, and a reference detector. Special sample requirements can often be met by changing the cell holder design or size. The system is fully supported by Brookhaven Instruments Corp.

Key features:

A      Both Dynamic light scattering (DLS) and Static light scattering SLS)
A      Large angular Range: 150 to 1550
A      Open Design/Standard Optical Rails
A      Heating and cooling Control
A      Filtration Assembly
A      Special Design Glass Vats: Specially polished and flat entrance window ensures minimum flare
A      Alignment Cell: Fine-screw vertical adjustment makes finding the center of rotation easier
A      Used He/Ne laser (632.8nm)
A      Highly efficient BI9000AT autocorrelator containing 522 selectable channels.
A      Multiple Laser Line Filters: Filter wheel with 632.8 (He/Ne), one open position for weak scatterers, and 2 blank (shutter) positions. Also available with 532 nm bandpass filter
A      Enhanced Viewing Optics: Coated, precision achromats coupled with behind-the-slit viewing and high-quality eyepiece make alignment easier
A      Additional Alignment Aperture: Alignment of laser much simpler and faster

 

Fig. 1 Alignment of LS instrument

 

Examples of Application:

   

Fig. 2 The graph shows the distribution of diameter of carbon nanotubes by Gaussian distribution (G(d)) and the cumulative distribution (C(d)).

 

 Fig.3 The graph shows a Guinier plot(q2 vs ln I-1)to calculate the radius of gyration from the slope. Similat to this plot, we can use the fractal plot (ln q vs ln I) to calculate fractal dimensions. In this figure I is scattered intensity and q is scattering wave vector (q= 4pnsin(q/2))/l).

 

Fig.4. Ms Du Ning is carrying out a DLS experiment.