Refractive Index - A Mixing Question Answered

In summary, the refractive index for a mixture will be somewhere in the middle of the two individual refractive indexes.
  • #1
lionelwang
23
0
Hi all,

I am thinking about the refractive index, if I have two components with refractive index n1 and n2, respectively, then I mix them up (chemical reactions might happen after the mixing), and should I expect a mixture with refractive index:n=a*n1 + b*n2, where a+b=1.
In other words, should the mixture refractive index (n) be somewhere between n1 and n2?

Need help, thank you very much!

Regards
 
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  • #2
If the two substances are totally 'mixable' (? right word ?) then that would work, I think. For gases, I guess you could assume it. If there is a chemical reaction during mixing, or even significant bonding between the two sets of molecules then you couldn't rely on it I'm sure. Also, you could get an emulsion which could affect the optical properties by making the mixture cloudy.

The refractive index for microwaves works that way, though. Varying the density of foam by altering the bubble size ( your a and b, effectively) can alter the refractive index and is used in coax cable and some microwave lenses, I believe.
 
  • #3
After I did some google work, I found that, approximately, that equation works, but yes, as you said, the change of the solid states, nonuniform density, or phase separation, etc. which will make the equation not valid for caculation of the mixture refrective index.

Thank you very much for your great answer.


sophiecentaur said:
If the two substances are totally 'mixable' (? right word ?) then that would work, I think. For gases, I guess you could assume it. If there is a chemical reaction during mixing, or even significant bonding between the two sets of molecules then you couldn't rely on it I'm sure. Also, you could get an emulsion which could affect the optical properties by making the mixture cloudy.

The refractive index for microwaves works that way, though. Varying the density of foam by altering the bubble size ( your a and b, effectively) can alter the refractive index and is used in coax cable and some microwave lenses, I believe.
 
  • #4
When they make graded index optical fibres, they must be using some variable mixture to get the grading so I guess the answer must be "sometimes you can".
 
  • #5
lionelwang said:
Hi all,

I am thinking about the refractive index, if I have two components with refractive index n1 and n2, respectively, then I mix them up (chemical reactions might happen after the mixing), and should I expect a mixture with refractive index:n=a*n1 + b*n2, where a+b=1.
In other words, should the mixture refractive index (n) be somewhere between n1 and n2?

Need help, thank you very much!

Regards

Given this statement, then no, you would not expect the refractive index to relate to the reactants at all.

For a pure mixture though (no reactions), this does hold true to a degree. Check out Cargille's website; they make a whole bunch of calibrated refractive index oils.

Claude.
 

What is refractive index?

Refractive index is a measure of how much a substance bends light as it passes through it. It is the ratio of the speed of light in a vacuum to the speed of light in the substance.

What factors affect the refractive index of a substance?

The refractive index of a substance is affected by its chemical composition, temperature, and the wavelength of light passing through it.

How is refractive index measured?

Refractive index is typically measured using a refractometer, which measures the angle that light bends as it passes through a substance.

What is the significance of refractive index in chemistry?

Refractive index is an important property in chemistry as it can help identify and characterize substances. It is also used in various industries such as optics, pharmaceuticals, and food science.

What is the relationship between refractive index and concentration?

The refractive index of a substance is directly proportional to its concentration. This means that as the concentration of a substance increases, so does its refractive index.

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