What is refractive index increment?
The refractive index increment (dn/dc) of a solution is a constant that indicates the variation of the refractive index with the solute concentration. It is used in the multi-angle light scattering technique to determine the concentration and the weight-average molar mass of polymers.
How is DN dc value calculated?
dn/dc values can be measured on-line with an RI detector, and also in a hyphenated GPC/SEC/gel filtration chromatography (GFC) light-scattering setup. This is a fast approach that often does not require additional sample.
Does molecular weight affect refractive index?
The molecular weight of polymers affects their refractive index, but its effect is not significant. In some polymers, as the molecular weight increases, the refractive index increases.
Why is DN DC important for GPC SEC?
Ultimately, the dn/dc value is important because it is the link that translates the raw RI signal to sample concentration. Taking advantage of the direct relationship between concentration and dn/dc value, there is a way to use the OMNISEC software to easily calculate an unknown dn/dc value.
What does the refractive index represent?
Refractive Index (Index of Refraction) is a value calculated from the ratio of the speed of light in a vacuum to that in a second medium of greater density. The refractive index variable is most commonly symbolized by the letter n or n’ in descriptive text and mathematical equations.
How is the index of refraction of a medium determined?
The refractive index of a medium (n) is equal to the speed of light (c) divided by the velocity of light through the medium (v). Rearranging the equation allows us to see the relationship regarding v. The lower the refractive index, the faster the velocity of light.
How does mass density affect refractive index?
Combined empirical and theoretical analyses show that a denser material generally tends to have a larger refraction index because the applied electric field induces a greater number of electric dipoles, and that the index–density relationship can be described reasonably well by the Lorentz–Lorenz relation.
Does refractive index depend on density?
As the density of a medium increases, its refractive index . As the density of a medium increases, its refractive index .
How does GPC calibration work?
Instrument calibration In GPC with light scattering, we calibrate the response of the concentration detector to a known concentration and the light scattering detector to a known molecular weight. Any time delay between the detectors, known as the inter-detector delay (IDD), is also determined at this point.
How do you increase refractive index?
It is obvious from the equation that increasing the refractive index by replacing the imaging medium from air (refractive index = 1.000) with a low-dispersion oil (refractive index = 1.515) dramatically increases the numerical aperture.
How is light affected by an increase in the index of refraction?
So as the index of refraction value increases, the optical density increases, and the speed of light in that material decreases.
How does refractive index relate to the density of a material?
Optical density is the measure of the degree to which a medium refracts light. Hence, if a material is optically denser then it will refract more light and will have a higher refractive index. Consequently, if a medium has lower optical density then it will refract less and will have smaller refractive index.
What happens to the refractive index when the density increases?
Answer and Explanation: The density of a substance will increase the refractive index of the substance (meaning light will travel slower through the substance).
Why does refractive index increase with density?
What is the difference between SEC and GPC?
It is exactly the same. Just two different ways to name it. It is the same thing. Gel permeation chromatography (GPC) is a type of size exclusion chromatography (SEC).