Effect of pH on the control of molecular orientation in monolayer of bent-core liquid crystal materials by Langmuir–Blodgett method

Abstract

Control of molecular orientation at the substrate surface is significant to understand the surface science. Langmuir films of bent-core liquid crystals having alkyl chains at both ends were deposited on silicon substrate. Studies were carried out on air–water interface by changing pH of the subphase. On compression, molecules were arranged in stacks at high pH where as uniform monolayer was formed at lower pH. Limiting area increased at low pH, which resulted in the formation of monolayer after attaining a sustainable surface pressure. Langmuir films were transferred to silicon substrate, and atomic force microscopy images showed appropriate height profiles.

Keywords:

• Langmuir–Blodgett films
• bent-core liquid crystal molecules
• isotherm
• atomic force microscopy

Acknowledgements

The authors wish to thank Ms L.K. Brar for many helpful discussions during this work. The valuable comments and suggestions from reviewers are also gratefully acknowledged.