What Are the Standard Molecules Used in Twisted Nematic LCD Displays?

[matheyrichs]

I've been looking into LCD technology recently and have found a ton of sites that explain how twisted nematic crystals guide polarization of incident light and how LCDs work in general. But no one seems to explain which molecules are in fact twisted nematic crystals.

can anyone tell me what some standard molecules used as twisted nematics are??

thanks!

 

[GCT]

Have you researched liquid crystals yet?

 

[matheyrichs]

Yes -- i actually started digging deeper and found more specifics -- looks like 5CB is a standard molecule used in LCDs.

I kept finding info saying that polar nematic crystals were used, but not the specific molecules. I thought maybe LCD manufacturers keep trade secrets on which compounds work well and what their properties are...

 

[chemisttree]

Twisted nematics can also be called cholesteric nematic materials. This group of nematics rotates plane polarized light somewhat and is used between polarized (visible, not electrical) plates to change the reflectivity of the display. The changes in reflectivity are manifest as dark/light or as a color. The name cholesteric refers to the first compound in the series to exhibit the property of 'twist' in the liquid crystalline state.

The first paper describing the electro active behavior of these twisted nematics (cholesterics) is found http://prola.aps.org/abstract/PRL/v28/i10/p593_1" . Sorry it is only an abstract but it is highly retrievable at your local library and well worth your effort.

 

[matheyrichs]

Looks like a great article! Luckily I'm on a college campus that has a lot of subscriptions to online journals and I'm able to view the full text no problem.

So standard LCD displays have issues with even spreading of light (due to polarization), creating the effect where you are able to move your head to a weird viewing angle and the display dims / disappears. I've heard mention that using circular polarizing methods instead of guiding linear polarization might be one method of improving this.

It seems to me that if you use the exact same setup but with a circular polarizer (say left-handed) instead of a linear polarizer at the beginning, wouldn't the TN-LC cell create a certain phase shift in the light based on whether it is twisted and "guiding" or not?

This isn't something I've spent any time researching (too busy with classes ending and final exams :p) but I'd love to know more about it if anyone knows about this research!