Light Scattering


Dynamic Light Scattering
Dynamic Light scattering is a method used for the determination of dynamics in a sample. By measuring the diffusion coefficient the hydrodynamic radius of particles in a size range between 1 nm up 1 µm can be obtained. A variety of samples from proteins over surfactant micelles to inorganic nanoparticles can be measured. The equipment can also be used for the detection of static light scattering.


Source and Optics
The light sources of the Dynamic Light scattering are a diode laser (Coherent Verdi V5, λ= 532 nm) with an adjustable power from 10 mW up to 5W or a Helium-Neon-Laser (Spectra Physics λ=632.8nm) with a fixed power of 25mW. The laser beam is focused with a lens on the center of the sample. 

Detection optics
The scattered light is detected by single-mode fiber detection optics (OZ from GMP, Zürich, Switzerland) or by a few-mode fibre detection optics (ALV, Langen, Germany) mounted on a goniometer. Depending on the size of the sample holder the scattered intensity can be measured at scattering angles between 10° and 160°. The data is acquired by a Perkin Elmer precisely Photon Counting Module (Perkin Elmer, Voudreuil, Canada) and an ALV 7002/USB Digital Multiple Tau Real Time Correlator (ALV, Langen, Germany) which allows a minimum time interval of 25 ns for the correlation function. 

Resolution
The hydrodynamic radius of samples with hydrodynamic radii between approximately 1 nm and 1 µm can be measured. The signal can be detected at scattering angles between 10-160°. 

Sample holder
Liquid samples are measured in cylindrical flasks. A minimum of 500µl of clear sample is necessary. 
In square cells the dynamic light scattering at 90° can be measured of only 30µl of sample solution. The sample holder is thermostated and the temperature can be adjusted between 5°C and 90°C. The sample is located in a index bath in case of the diode laser system. 

Software
The ALV software package is used to record and store the correlation functions. 
 



Small Angle Static Light Scattering
Static light scattering is a method to obtain structures in the size range of hundreds of nm up to several µm. the size, shape and size distributions of various samples such as emulsion droplets and inorganic particles can be measured. The small angel light scattering apparatus (SALSA) was created especially for samples with higher particles sizes (up to 10µm) and/ or high concentration. The flat cell and the construction of the apparatus enable the measurement of low angles (down to ~1°) even for turbid samples.  For higher scattering angles the goniometers described in the Dynamic Light Scattering section can be used.
 

Source and Optics
The light source used is a GLG5360 Helium-Neon Laser with a fixed power of 10mW (NEC Corporation, Tokyo, Japan, P=10mW, λ=632.8nm). 
Detection optics:
The scattered light is detected by an array consisting of 160 photodiodes for simultaneously detecting scattering curves from 1° to 60°.

Resolution
The scattered light can be measured at scattering angles between 1° to 60° (Scattering vector in water 2.3*10-4 – 1.3*10-2 nm-1). This allows to measure samples with particle sizes between a few hundred nanometers up to about 10 μm.

Sample holder
The sample holder consists of a flat cell with a variable thickness of 15 μm up to 5 mm. The flat cell is located in an index bath equipped with an optical lens which enables the measurement of angles higher than the critical angle of the glass-air interface. 
The sample holder is thermostated and the temperature can be adjusted between 5°C and 90°C. 

Software
The SALSA32 software is used to record and store the scattering curves. In the CONSALIK program the raw data is processed by background subtraction, correction of the signal intensities and calculation of the scattering vectors from the scattering angle.