(+) 10E4M6 : a critical A-C* and the first C*-hexatic B liquid crystal phase transitions

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Abstract
We have determined that the C* phase in (+)10E4M6 (4'-(4-methylhexyloxy)phenyl 4-decyloxybenzoate) occurs between two orthogonal phases : an A phase above 70 °C and a hexatic B phase below 31.3 °C. The C*-A transition shows very little temperature hysteresis and seems continuous with a large anomalous heat capacity. X-ray measurements of the tilt angle, θ, in the C* phase could be described by θ ∼ (TCA - T)β with β = 0.32 ± 0.08, TCA, the C*-A transition temperature. In comparison, a non-chiral analogue of (+)10E4M6 called 10E6 (4'-hexyloxyphenyl 4-decyloxybenzoate), exhibited a much smaller specific heat jump at the C-A transition and β = 0.35 ± 0.07. The C*-hexatic B transition is monotropic and discontinuous. Two lengths coexist in the transition region corresponding to a change in tilt angle from 23° to zero. Strong anchoring conditions of the director orientation by surface treatment forces the layers to reform at the C* to B transition. This is the first unequivocal observation in the polarizing microscope of the reformation of smectic layers at a transition between two smectic phases