I am confused about the terms of “pitch distance" and “visible wavelength” in chiral nematic structure as cellulose nanocrystal (CNC).
When we see the iridescent color from CNC film, this is because of “half-pitch” or “pitch” distance that fall into visible wavelength (Bragg reflection)?
From the equation lambda=nP, it seem like the distance of “full turn pitch” is the answer.
However, with the chiral nematic structure, some literature said “half-pitch” is the answer, because the repeating band is every single “half-pitch”.
So, is there anyone suggest me that which one is the right relationship.
For example,
the chiral nematic film is blue color (absorb wavelength @ 620–750 nm). It means that the structure of this chiral nematic film should have “pitch at about 620–750 nm” or “half pitch at about 620–750 nm” ?
The pitch is the distance along z and perpendicular to the pseudo-layer over which the molecules rotate 360 degrees. p/2 is the distance where molecules rotate 180 degrees (as seen in the attached picture). In cholesteric liquid crystals, one handedness of light (either right-handed circularly polarized right or left-handed circularly polarized light) reflects over a certain spectrum range. The reflective spectrum is :
pitch*ordinary refractive index < Lamda < pitch*extraordinary refractive index
-ordinary refractive index is called "no" and extraordinary refractive index is called "ne"
Pitch is the total distance by which molecules rotated by 360 degree.In the formula pitch is full length.
- Badges
- Science topic
- Similar topics
- Biological Science
- Bioecology
- Systems Ecology
- Landscape Ecology
- Connectivity