An Investigation of Dielectric Permittivity as Related to Concentration in Mixtures of 7CB and MBBA

Michael Christopher Davis


This study measured the effects on dielectric permittivity by changing concentrations of a mixture between 4-n-heptyl-4'cyanobiphenyl, 7CB, and 4-methoxybenzylidene-4-butylanaline, MBBA. For each mixture, the phase transition was recorded using a digital video camera, while the temperature was monitored using a thermistor and the computer program LabVIEW. Using the reduced temperature of 0.015, we calculated a temperature for each mixture that was in the nematic phase proportionally equal to all the other concentrations. At the calculated temperatures we measured epsilon perpendicular and epsilon parallel by modeling the liquid crystal cell as a capacitor and resistor in parallel. Epsilon parallel and epsilon perpendicular gave reliable results when compared to the literature values of pure 7CB. Delta epsilon showed a distinct exponential decay as the concentration of 7CB in the mixture decreased. When compared to a similar mixture of 5CB-MBBA, the values for delta epsilon are almost identical for each concentration.