The polarized-light micrograph in the attachment corresponds to an ionic liquid crystal material based on ion pairing of dicationic 4,4' bipyridinium capping two thymine groups with amphiphilic anion 3,4,5-tris(dodecyloxy)benzene sulfonate. The picture was recorded on the microscope after recrystallization from isotropic state (100°C). Which kind of texture i can speculate from this texture?
It looks like nematic LC dropplets with the director arranged in a radial structure. I'm not an expert on that but see papers by Miller and Abbott on LC dropplets.
Good Luck!
Well, it's not as simple as that, Marco. Of course the characteristic "maltese cross" texture indicates full rotational symmetry (see attached). But it's equally possible to have concentric-shells as the radial-director configuration. Even if they used phase contrast microscopy with the retardation plate (thus distinguishing radial from circular arrangement) - it will only tell the structure of birefringence axis, but who can tell whether this is a positive or negative dielectric anisotropy material?
It all must start from more clarity on what this molecule is doing. I am not sure how this material could form a nematic - perhaps only if it forms long aggregated filaments of stacked planes? But I can easily see a smactic, or a discotic / columnar conformation possible (Marius should know better what shape the molecule takes on assembly).
To be fair, I also think that these "droplets" are not liquid crystalline in the picture (they may have been at some stage of their life) - they look more like "spherulite" arrangement of lamellar crystals (which again is possibly more compatible with the structure of his molecule).
Dear Prof. Terentjev, thank you for your detailed comment! I come with some additional info:
The wedge-shaped anion 3,4,5-tris(dodecyloxy)benzene sulfonate (DOBS) when paired with cations such Li, K, Cs etc adopts columnar arrangement in LC state (http://www.tandfonline.com/doi/abs/10.1080/02678290802376107).
I may expect also an columnar mesophase for my compound?
In fact my deep effort is to understand how the "thymine" moieties attached to the bipyridinium core may affect the supramolecular arrangement in LC state by comparing with the1,1'.dimethyl-4,4'-bipyridinium analogue (see attached figure). This compound shows also columnar type mesophase according with some molecular modelling (http://dx.doi.org/10.1039/C2JM31830J).
http://www.tandfonline.com/doi/abs/10.1080/02678290802376107
http://dx.doi.org/10.1039/C2JM31830J
I agree Profesor Terentjev.
II can suggest to use X-ray diffraction(even wide angle technique) to distinguish nematic droplets (which must appear as a broad halo, or reflection missing on X-ray diffractogram) or spherulite (which must give clear reflections on X-ray diffractogram).
Hi there!
Well, from the picture, it looks like a crystalline sample which might arrange in lamellae or columns due to phase separation between the long alkyl tails and the aromatic moieties.
I would suggest performing X-ray, where in the medium angle region peaks should come up. The relation between these peaks will tell you whether you have lamellar or columnar phases (or even others). From the wide angle region, the crystalline or amorphous nature of your sample will show up.
SALUT!
Welcome!
Your sample is definitely not nematic.
Glad to assist you.
SALUT!
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