Critical behaviour of the anchoring energy of the director at the free surface of a nematic liquid crystal

A new structural transition occurs at the free surface of some nematic liquid crystals when the temperature reaches a critical value T₀. In this work we study the temperature dependence of the anchoring energy of the director at the free surface close to the critical point. We find that the anchoring energy tends to zero with the critical exponent δ = 1 when the temperature approaches the critical value T₀. The experimental results are interpreted in terms of the Parsons and Mada theories.