Surface and flexoelectric polarization in a nematic liquid crystal directly measured by a pyroelectric technique

An alternative, pyroelectric effect based technique was developed for the direct measurement of the surface polarization in homogeneously and homeotropically oriented nematic cells as well as for the measurement of the flexoelectric polarization in hybrid aligned nematic cells. The pyroelectric response was measured with a modulated beam of a diode laser, absorbed by a dye incorporated in a standard liquid crystal 4-pentyl- $4^{\prime }$-cyanobiphenyl. The dye provided a gradient of the temperature increment along the cell normal, which allowed for the separation of pyroelectric contributions from both the opposite surfaces and the bulk. The signs and absolute magnitude of the polarizations mentioned have been found over the entire temperature range of the nematic phase.