Structural study of a bent-core liquid crystal showing the B1-B2 transition

An experimental study of the B-1-B-2 transition is carried out in a bent-core liquid crystal. The study is essentially based on x-ray measurements as a function of temperature. The B-1-B-2 transition is extremely unusual and implies a deep structural change from a columnar phase to a lamellar phase. We have found that the B-1 phase in our compound is similar to the so-called B-1 reversed phase, with an additional splay of the polarization in the columns. On approaching the B-2 phase the width of the cross section of the columns increases. The transition is clearly first order, with a large hysteresis though the enthalpy content is very small. A possible mechanism for the transition is briefly sketched.