New ester-type banana (bent-shaped) monomers, 1,3-phenylene bis[4’-(alken-1-yloxy)-biphenyl-4-carboxylate]s Ia-Vb, with different substituent(s) on the central phenyl ring (H, CH3, Cl or NO2) and alkenyl tails in the side arms (decenyl or undecenyl) were prepared. The analogues IIIa-IVb with 4-chloro- or 4,6-dichloro-substituents exhibited a nematic phase, while Va,Vb with 2-nitro-substituent showeda B7 phase at relatively low temperature. All the compounds were stable, no degradation or polymerization was observed under applied electric fields or heat treatments. Electro-hydrodynamic instabilities were observed in the nematic phase of each sample. In the B7 phase of Vb there was an electro-optical switching in the range 112-114.5 °C with switching time of about 150 ms at 20 V/mm field. At lower temperatures no electro-optical switching occurred, but a ferroelectric-type spontaneous polarization of 22 nC/cm2 could be detected. The bend angle was calculated by the semiempirical CAChe/MOPAC/PM5 method.
|Autori interni:||GALLI, GIANCARLO|
|Autori:||K. Fodor-Csorba; A. Vajda; A. Jákli; C. Slugovc; G. Trimmel; D. Demus; E. Gács-Baitz; S. Holly; Galli G|
|Titolo:||Ester type banana-shaped liquid crystalline monomers: Synthesis and physical properties|
|Anno del prodotto:||2004|
|Appare nelle tipologie:||1.1 Articolo in rivista|