A new liquid crystal of a siloxane dimer with an achiral swallow-tail, C11Si2C11, D, was synthesized and mixed with a chiral material as a chiral dopant, 4'-[11-(1,1,2,2,3,3,3-heptamethyltrisiloxanyl)undecyloxy]biphenyl-4-carb oxylate, C11Si3, C, to prepare binary mixtures for this study. All mixtures possess the ferroelectric chiral smectic C phase over a broad temperature range. For respect compound C11Si3, the temperature range of the SmC* phase was only 72.6 degrees C, and was increased upon the addition of dimer C11Si2C11. The electro-optical properties of the SmC* phase, such as tilt angle, dielectric permittivity and switching behavior were also measured. It appeared that the mixtures had a similar viscosity, but the switching time was decreased due to the larger P-s, which was caused by an increased proportion of C11Si3, Therefore, the mixtures revealed a similar tilt angle at around 37.5 degrees at temperatures within their respective mesophase temperature ranges. As a consequence, the correlation between the electro-optical properties and mixture proportion was determined. (C) 2010 Elsevier B.V. All rights reserved.