Pattern formation in Langmuir–Blodgett films of tricycloquinazoline based discotic liquid crystal molecules

• Tricycloquinazoline based amphiphilic discotic liquid crystal (AmTCQ) molecules.
• Langmuir–Blodgett (LB) films of AmTCQ molecules at different surface pressures.
• Nucleation and aggregation of the molecules leading to triangular domains.
• Triangular domains increase in number with increasing deposition pressure.
• Triangular domains remain undistorted till the deposition pressure <20 mN/m.

The assembly of molecules on the surface has drawn considerable attention because of its potential to tailor the physicochemical, electronic, and magnetic properties of materials. The structure of aggregates of molecules can be influenced by the molecular interactions and the external parameters like temperature, pressure and ion contents. We have found a stable Langmuir monolayer of amphiphilic tricycloquinazoline based discotic liquid crystal (AmTCQ) molecules at air–water (A–W) interface. The monolayer exhibits gas phase, low density liquid phase and high density liquid phase. The structural evolution in Langmuir–Blodgett (LB) films of the AmTCQ molecules as a function of target surface pressure is studied using an atomic force microscope. We found aggregation of the discotic molecules leading to nucleation sites at a lower surface pressure. With the increasing surface pressure, each nucleation site grows to form a stable triangular structure. The shape and size of the triangular structure remain stable till the target surface pressure for LB films deposition exceeds the equilibrium surface pressure of the AmTCQ molecules. The number of triangles in the film increases with increasing target surface pressure of LB deposition. The target surface pressure of LB deposition acts as a controlling parameter for obtaining desired number of triangular domains in the film.

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