CRITICAL-BEHAVIOR AT NEMATIC SMECTIC-A(1) PHASE-TRANSITIONS .2. PREASYMPTOTIC 3-DIMENSIONAL XY ANALYSIS OF X-RAY AND CP DATA

X-ray data are reported for the nematic phase near the nematic (N)-smectic-A1(Sm-A1) transition in a binary mixture of pentylphenylcyanobenzoyloxy benzoate (DB5CN) + cyanobenzoyloxypentylstilbene (C5 stilbene). These data and x-ray data from four other N-Sm-A1 systems, plus the corresponding high-resolution C(p) data, are analyzed using the exact solutions of preasymptotic three-dimensional (3D) XY theory. The correlation volume xi(parallel-to)xi(perpendicular-to)2, smectic susceptibility sigma, and heat capacity C(p) are in good agreement with preasymptotic theoretical predictions. First-order corrections-to-scaling terms were known previously to be important for describing C(p); their importance for xi(parallel-to)xi(perpendicular-to)2 and sigma is demonstrated here. Many universal features of the 3D XY model are confirmed by the present self-consistent analysis, but the critical anisotropy of the individual lengths xi(parallel-to) and xi(perpendicular-to) and the fact that C(p) exhibits a normal XY amplitude ratio rather than the theoretically predicted inverted ratio are still unresolved issues.