I put 1 microL of CB5 (LC) between two glass slides. No treatment was done on the slide surfaces. I viewed the sample under cross polarization condition. Attached is my observation at two different location on the slide. What puzzled me is why A differ than B?. From my knowledge A is called schlieren texture. I did some reference said that B is called thread-like texture. My questions are
(1) Is B called schlieren texture too?
(2) Why I got different texture, A & B, eventhough they are on the same slide.
*Both images are of the same scale.
Thanks
Both pictures show schlieren textures. You're using a cholesteric (CB5) so don't expect to see thread-like ('nematos' = nematic) structures.
The extent and form of the textures is dependent on bunch of factors. Glass cleanliness is important and it's easier to see that the textures on the right (picture B) are in an area of much higher particulate contamination or debris. The other factor is the distance between the 2 glass plates. This will allow the pitch of the cholesteric to unwind. What was your cell spacing (i.e. the thickness of CB5)?
Both A and B represent schlieren texture. There are several factors like cleaning status of glass slide, thickness, uniformity of sample if you are taking a large area on glass slides, which affect the optical textures as described by Dr. Alan F Rawle.
If you want to repeat the POMs, take a unaligned cell of uniform thickness and observe the POM. Cell thickness will also play a role wrt to pitch value.
TQ for your response: both Alan & Dharmanendra,
This is my first time handling LC.
As for the cell thickness, I did not measure. No spacer was used between slides.
So, lesson I have to learn
- slide cleanliness
- cell thickness control
Another question, Is CB5 nematic or cholesteric? The supplier (Sigma Alderich) state it is nematic.
You are correct - CB5 is nematic. I initially read CB15 which is cholesteric.
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