Viscosities of a bent‐core nematic liquid crystal

Viscosity measurements are reported for a bent‐core nematic liquid crystal, 4‐ chloro‐1,3‐phenylenebis{4‐[4′‐(9‐decenyloxy)benzoyloxy]} benzoate (ClPbis10BB). The rotational viscosity was measured by analysing the dynamics of director rotation in pulsed magnetic fields, and the flow viscosities were determined by employing a new electro‐rotation technique. The results show that whereas the rotational viscosity is more than ten times larger than for calamitic liquid crystals, the flow viscosity is more than 100 times larger. Even more striking is the difference between the ratio of the flow and rotational viscosities, which for calamitic nematics is typically 0.1, whereas in this bent‐core material it is ∼50. This suggests that the large shear viscosity is primarily due not so much to the molecular size, but rather the shape. A model is discussed that may explain the observations.