| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 608361 | Journal of Colloid and Interface Science | 2012 | 10 Pages |
Langmuir films of facial T-shaped amphiphilic liquid crystals were studied at the air–water interface. The liquid crystals were composed of three incompatible segments: a central rigid rodlike p-terphenyl (TP) group, two flexible hydrophobic n-alkyl terminal chains of identical length linked through ether bonds, and one hydrophilic lateral chain of three ethylene oxide units with a carboxyl end group. In order to determine the influence of the alkyl chain length on the characteristics of condensed films three TPs having n-alkyl chains with eight (TP8/3), ten (TP10/3) or 16 (TP16/3) carbon atoms were investigated. Surface pressure – mean molecular area isotherms revealed clear differences. TP8/3 and TP10/3 exhibit an extended plateau region where a phase transition from monolayer to multilayer takes place. On the other hand, the TP16/3 isotherm showed a distinct maximum (‘spike’) corresponding to a surprising surface crystallization process which is reported for the first time for a Langmuir film of a liquid crystal. Brewster angle microscopy clearly confirmed these differences: TP8/3 and TP10/3 formed circular domains with liquid crystalline order, while TP16/3 formed well-defined two-dimensional polycrystalline spherulites which are fractured after further compression. The film thickness determined by X-ray reflectivity measurements correlated with a multilayer formation for TP10/3. The morphology of Langmuir–Blodgett (LB) films transferred onto silicon wafers and studied by atomic force microscopy also confirmed the striking different behavior (multilayer formation vs. 2D crystallization) of the TPs under investigation.
Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (90 K)Download as PowerPoint slideHighlights► Facial T-shaped p-terphenyl derivatives amphiphilic liquid crystals studied at air–water interface. ► Different behavior of liquid crystals depends on their n-alkyl chain lengths. ► Liquid crystals with short n-alkyl chains form fluid multilayers at air–water interface. ► Liquid crystals with long n-alkyl chains crystallize in spherulitic structures. ► Spherulitic surface crystallization process reported for the first time for a Langmuir film of a liquid crystal.
