Morphology,electro-optical and dielectric properties of polymer network liquid crystals in visible wavelengths

The correlations among electrical, optical properties and polymer morphologies of polymer network liquid crystals (PNLCs) constructed with various curing parameters are investigated. The experimental results indicate that high UV curing intensity, low curing temperature and high monomer-dopant concentration reduce the sizes of liquid crystal (LC) domains, thereby decreasing field-off response time and light scattering and increasing phase retardation of the PNLC cells. Photoinitiator concentration affects the LC domain size as well. For instance, increase in photoinitiator concentration results in the acceleration of polymerisation and thus decreases LC domain size. This effect increases driving voltages of the PNLC cells. Notably, excessive amounts of photoinitiator increases the LC domain size of the PNLC cell. Furthermore, dielectric measurement reveals that decrease in the LC domain size generally increases the dielectric relaxation frequency of the PNLC cells. When the LC domain size is small enough, the dielectric relaxation frequency of the PNLC cell is further dominated by the monomer concentration owing to the increased densities of polymer networks that facilitate the alignment of LC molecules.