Low-angle laser light scattering or LALLS is an application of

light scattering Scattering is a term used in physics to describe a wide range of physical processes where moving particles or radiation of some form, such as light or sound, are forced to deviate from a straight trajectory by localized non-uniformities (including ...

that is particularly useful in conjunction with the technique of

Size exclusion chromatography Size-exclusion chromatography (SEC), also known as molecular sieve chromatography, is a chromatographic method in which molecules in solution are separated by their size, and in some cases molecular weight. It is usually applied to large molecul ...

, one of the most powerful and widely used techniques to study the molecular mass distribution of a polymer. Typically the

eluent In analytical and organic chemistry, elution is the process of extracting one material from another by washing with a solvent; as in washing of loaded ion-exchange resins to remove captured ions. In a liquid chromatography experiment, for exa ...

of the SEC column is allowed to pass through both a

refractive index In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, o ...

detector A sensor is a device that produces an output signal for the purpose of sensing a physical phenomenon. In the broadest definition, a sensor is a device, module, machine, or subsystem that detects events or changes in its environment and sends ...

(that gives measures for the concentration in the solution as a function time) and through a laser scattering cell. The scattered intensity is measured as a function of time under a small angle with respect to the laser beam. The low-angle light scattering data can be analyzed if one assumes that the low-angle data is the same as the scattering at zero angle. For the relevant equations, see the article on

static light scattering Static light scattering is a technique in physical chemistry that measures the intensity of the scattered light to obtain the average molecular weight ''Mw'' of a macromolecule like a polymer or a protein in solution. Measurement of the scattering ...

. Under these conditions the laser signal together with the concentration data can be translated into a curve that yields both the M_n and the M_w, the molar mass weighted by number and by weight respectively. The combination of those two data gives information on the linearity of the polymer. The technique is sometimes complemented or combined with

viscometry A viscometer (also called viscosimeter) is an instrument used to measure the viscosity of a fluid. For liquids with viscosities which vary with flow conditions, an instrument called a rheometer is used. Thus, a rheometer can be considered as a s ...

and polystyrene standards are availablestandards
/ref> for validation of the results.

References

Polymer physics Scattering {{scattering-stub