offzuloo.blogg.se - Dynamic light scattering theory

Differential cross section measurements were commonly made, for example, to study the structure of the atomic nucleus by scattering from them nucleons, such as neutrons. The then-conventional use of a single detector rotated about an illuminated sample with intensities collected at specific angles was called differential light scattering after the quantum mechanical term differential cross section, σ(θ) expressed in milli-barns/steradian. It permitted the entire range of scattered intensities to be recorded on the film with a subsequent densitometer scan providing the relative scattered intensities. An interesting system based upon the use of high speed film was developed by Brunsting and Mullaney in 1974. Multiple detectors having different quantum efficiency have different response and hence needs to be normalized in this scheme. Since the collection of data was made as the detector was placed at different locations on the arc, each position corresponding to a different scattering angle, the concept of placing a separate detector at each angular location of interest was well understood, though not implemented commercially until the late 1970s. Measurements were generally expressed as scattered intensities or scattered irradiance. The first commercial instrument (formally called a "scattered photometer") was the Brice-Phoenix light scattering photometer introduced in the mid 1950s and followed by the Sofica photometer introduced in the late 1960s. Historically, such measurements were made using a single detector rotated in an arc about the illuminated sample. The measurement of scattered light from an illuminated sample forms the basis of the so-called classical light scattering measurement.

3.3.3 Branching and molecular conformation.

A discussion of the physical phenomenon related to this static light scattering, including some applications, data analysis methods and graphical representations associated therewith are presented. The "multi-angle" term refers to the detection of scattered light at different discrete angles as measured, for example, by a single detector moved over a range that includes the particular angles selected or an array of detectors fixed at specific angular locations. In recent years, since all commercial light scattering instrumentation use laser sources, this need to mention the light source has been dropped and the term MALS is used throughout. Until the advent of lasers and their associated fine beams of narrow width, the width of conventional light beams used to make such measurements prevented data collection at smaller scattering angles. The insertion of the word laser was intended to reassure those used to making light scattering measurements with conventional light sources, such as Hg-arc lamps that low-angle measurements could now be made. A collimated beam from a laser source is most often used, in which case the technique can be referred to as multiangle laser light scattering ( MALLS). It is used for determining both the absolute molar mass and the average size of molecules in solution, by detecting how they scatter light. Multiangle light scattering ( MALS) describes a technique for measuring the light scattered by a sample into a plurality of angles.

( May 2014) ( Learn how and when to remove this template message) Please help improve it to make it understandable to non-experts, without removing the technical details. This article may be too technical for most readers to understand.