Integrated X-Ray-Scattering Intensity Measurement of the Order Parameter at the Nematic-to-Smectic-A Phase Transition

Abstract

The temperature dependence of the square of the smectic order parameter, (\mid \psi \mid^2), was determined from the integrated x-ray scattering intensity. The data are described very well by the form (I(t)/I(0)=1 \mp A^{(\pm)}\mid t \mid^x), where (t=(T-T_{NA})/T_{NA}). The determined values for x do not agree with the theoretically expected value (x=1-\alpha), where (\alpha) is the heat-capacity exponent. This disagreement raises questions concerning the quantitative validity of the Landau–de Gennes free energy.