Homeotropic orientation behavior of nematic liquid crystals induced by copper ions

• The copper ions are coated on the surface of substrates directly without self-assemble, the cost is dropped remarkably.
• Optical images are characterization by MATLAB, which provide a base for quantitative analysis in further experiment.
• The proposed film is simple and can detect DMMP with good reversibility.

A homeotropic ordering film of nematic liquid crystal (LC) induced by copper ions (Cu2+) had been developed. The Cu(ClO4)2 was directly spin-coated on the glass substrate without any other chemical modification. A homeotropic orientation of LC thin-film was generated by the interfacial chemical interaction between nitrile-containing LC and copper ions on the surface. Results showed that an appropriate density of Cu2+ could shorten the response time of orientation, but a shelf-time was prolonged. The LC film fabrication not only offered a simple process, but also presented a great repeatability to detect organophosphonates (DMMP). This study provided guidance for the design of LC films responding to organic molecules as a biosensor.