Measurement Principles
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.
Dynamic & Static Light Scattering (DLS/SLS)
In the SLS mode, time-averaged intensity measurements are made – at either fixed or variable angles – in the range from 8° to 155° 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 such topics as:
- Mw Molecular weight determinations
- Rg Radius of gyration
- A2 Determination of second virial coefficient
- Micro-emulsion technology
- Colloid behavior
- Complex fluid characterization
- Emulsion polymerization
- Particle size growth
- Nucleation processes
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).
From these DLS measurement many interesting subjects may be explored, among them:
- Particle size distributions
- Particle aggregation phenomena
- Micellar systems
- Micro-emulsion technology
- Colloid behavior
- Vesicles & liposomes
- Plasmid DNA’s
- Particle size growth
- Nucleation processes & protein crystallization
Specifications
Beam Focus and Steering | Includes mounts, adjustments, and apertures |
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Turntable | 200 mm O.D. turntable, worm gear, and ball bearnings; manual or automatic selection of angles in 0.01° steps; precision machine base with mounting holes; positioning table with micrometer adjustments (power supply and controller for stepping motor is optional) |
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Specimen Cell Assembly | Including thermal enclosure, centering adjustments, seperate plumbing for temperature control and index matching liquids, round cell holders, square cell holder and alignment cell |
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Index Matching Vat | With optically flat and specially polished entrance window, precision machined and annealed to minimize stray light |
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Periscopic Beam Stop | Located inside vat to prevent flare from exit window; provided with coupling for use with optional, zero-angle reference detector |
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Main Detector Optics | - Entrance aperture 3 mm
- Coated, adjustable achromat for focusing scattered light onto 200 micron slit; slit position adjustable
- Reflex mirrow and high quality eye piece for viewing scattering region through slit
- Filter turret with 637, 532, 633, 514 and 488nm narrow band pass filters and 100, 200, and 400 micron, 1, 2, and 3 mm pinhole for SLS & DLS measurements.
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A policy of continual improvement may lead to specification changes.