The variation of helical pitch in multicomponent liquid crystal mixtures is derived using the concept of the longhyphen;range distortions induced by chiral molecules in a nematic matrix. The pitch in a mixture is a quadratic function of the number densities of component molecules of given molecular twisting powers. The pitch variation becomes a linear function of number densities only when the twisting powers satisfy certain special conditions. The nonlinear pitch relation formulated herein is shown to describe typical experimental data on nematicndash;cholesteric mixtures and allows determination of experimental values of the molecular twisting power.
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