OBSERVATION OF TEXTURES OF NEMATIC POLYMERS AND ESTIMATION OF THE ELASTIC-CONSTANTS

The texture of a copolyesteramide, Vectra(R) B950, has been studied by optical microscopy. At rest, the defects are typical of a biaxial nem atic phase, but under the influence of a magnetic field or under shear , the nematic transforms into a uniaxial phase. The Freedericksz geome try yields a K(I) elastic constant of the order of 10(-8)N. The diffus ivities K(III)/(eta) and K(II)/(eta) are obtained by measuring the lig ht intensity transmitted through a sample during shear start-up and re laxation, and from this we estimate K(III) congruent-to 10(-9)N and K( II) congruent-to 10(-10)N. Since the biaxiality is small, these uniaxi al constants adequately describe the phase at rest.