Viscoelasticity, dielectric anisotropy, and birefringence in the nematic phase of three four-ring bent-core liquid crystals with an L-shaped molecular frame

• Published in: Soft matter Vol. 9; no. 4; pp. 166 - 175
• Main Authors: Avci, Nejmettin, Borshch, Volodymyr, Sarkar, Dipika Debnath, Deb, Rahul, Venkatesh, Gude, Turiv, Taras, Shiyanovskii, Sergij V, Rao, Nandiraju V. S, Lavrentovich, Oleg D
• Format: Journal Article
• Language: English
• Published: 01.01.2013
• Subjects: Anisotropy; Asymmetry; Birefringence; Dielectric constant; Dielectrics; Liquid crystals; Nematic; Viscosity
• ISSN: 1744-683X; 1744-6848
• DOI: 10.1039/c2sm26448j

Molecular shape is an important factor in determining the material properties of thermotropic liquid crystals (LCs). We synthesized and investigated several LC compounds formed by asymmetrically bent molecules with a rigid four-ring core in the shape of the letter 'L'. We measured the temperature dependencies of dielectric permittivities, birefringence, splay K 1 and bend K 3 elastic constants, splay viscosity η splay and flow viscosities η || and η . The bend-splay anisotropy δ K 31 = K 3 − K 1 is negative, similar to the case of nematic LCs formed by symmetrically bent molecules of V-shape. The dielectric anisotropy Δ and birefringence are positive in the entire nematic range. The splay viscosity η splay and the flow viscosities η || and η are smaller than the viscosities measured for the symmetric V-shaped bent-core materials at similar temperatures. The ratio Γ = η splay / η ||, is in the range 5-4 that is typical for rod-like LCs. The reported L-shaped bent-core nematic LCs combine the useful features of bent-core LCs (such as a negative δ K 31 , suitable for formulation of broad-range blue phases) with the relatively low viscosities, a property typical for rod-like LCs and beneficial for electro-optic switching applications. New L-shaped bent core mesogens with four phenyls show a broad temperature range uniaxial nematic phase and properties intermediate between the rod-like and V-shaped bent-cores.