Specific Heat Due to Smectic-C to Smectic-l Bond Orientational Ordering

Abstract
A high-resolution calorimetric study of methylbutylphenyloctyloxybiphenyl carboxylate (8OSI) has been carried out near the smectic-C to hexatic smectic-I transition. The excess heat capacity peak ΔCl , is large but clearly rounded over a 300 mK range. The ΔCp data and previously published Co order parameter data can be fit simultaneously using a phenomenological equation of state with a temperature independent tilt field H. Interpretation of the underlying effective critical exponents α = 0.47 and β = 0.077 is not clear, but one possibility is that the SmC‒SmI transition in the limit H → 0 would be weakly first-order.