Although this method is extremely versatile, there are numerous key factors that cannot be ignored when employing light scattering to characterize high-concentration solutions.Īlthough it is feasible to take measurements on high volume-fraction samples without dilution, additional questions arise regarding the meaning of the hydrodynamic size. Static light scattering assumes that each detected photon has only been scattered exactly once.Sponsored by Brookhaven Instruments Corporation Abstractĭynamic Light Scattering (DLS) is an efficient method of measurement employed for calculating the hydrodynamic size of common nanomaterials consisting of nanoparticles, colloids, polymers and proteins. In macromolecule solutions, for instance, it can assume negative (particle-particle interactions are favored), zero, or positive values (particle-solvent interactions are favored). This parameter describes the interaction between particles and the solvent. An advantage of the Debye plot is the possibility to determine the second virial coefficient. For polydisperse samples, the resulting molecular mass from a static light-scattering measurement will represent an average value. The intercept of the fitted line gives the molecular mass, while the slope corresponds to the 2 nd virial coefficient.Īs the Debye plot is a simplification of the Zimm equation, the same limitations of the latter apply, i.e., samples should present a monodisperse nature. By acquiring data on concentration and scattering intensity, the Debye plot is constructed by plotting Kc/ ΔR(θ) vs. Note that this is also the result of an extrapolation to zero scattering angle. It is convenient to normalize all the detectors to the 90° angle detector. Since isotropic scatterers scatter the same intensity at any angle, the detector efficiency and gain can be normalized with this procedure. Then an isotropic scatterer is added to the solvent. To normalize the detectors, a measurement of a pure solvent is made first. In this case, a normalization of the detectors is absolutely needed. Usually, detectors will have slightly different quantum efficiency, different gains, and are looking at different geometrical scattering volumes. 2.6 Composition-gradient static light scatteringįor a light scattering instrument composed of many detectors placed at various angles, all the detectors need to respond the same way.Since this is impractical, all commercial instruments are calibrated using a strong, known scatterer like toluene since the Rayleigh ratio of toluene and a few other solvents were measured using an absolute light scattering instrument.
#Dynamic light scattering continuous full#
To measure the average molecular weight directly without calibration from the light scattering intensity, the laser intensity, the quantum efficiency of the detector, and the full scattering volume and solid angle of the detector need to be known. Additional details on the history and theory of MALS may be found in multi-angle light scattering. Hence simultaneous measurements at several angles relative to the direction of the incident light, known as multi-angle light scattering (MALS) or multi-angle laser light scattering (MALLS), are generally regarded as the standard implementation of static light scattering. The angular dependence is required to obtain accurate measurements of both molar mass and size for all macromolecules of radius above 1–2% of the incident wavelength. One or many detectors are used to measure the scattering intensity at one or many angles. Static light scattering is also commonly utilized to determine the size of particle suspensions in the sub-μm and supra-μm ranges, via the Lorenz-Mie (see Mie scattering) and Fraunhofer diffraction formalisms, respectively.įor static light scattering experiments, a high-intensity monochromatic light, usually a laser, is launched into a solution containing the macromolecules. By measuring the scattering intensity for many samples of various concentrations, the second virial coefficient, A 2, can be calculated. Measurement of the scattering intensity at many angles allows calculation of the root mean square radius, also called the radius of gyration R g. Static light scattering is a technique in physical chemistry that measures the intensity of the scattered light to obtain the average molecular weight M w of a macromolecule like a polymer or a protein in solution.
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