Defects induced by anchoring transitions of nematic fluids at solid and gas interfaces

•Anchoring transitions were found in nematic fluids at solid and at air interfaces.•A method to find anchoring transitions was established based on sessile droplets.•Optical simulations were done to understand the restructuring of director field.•Discontinuous, continuous, and re-entrant anchoring transitions were identified. Temperature triggered anchoring transitions in nematic liquid crystals have been investigated at solid, as well as at air interfaces. We established a searching algorithm based on sessile droplets allowing an efficient discovery of compounds that show orientational transitions. We have identified two types of the transition, one on the coated substrate and another at the free surface bounded by air. As a consequence of the two types of anchoring transitions, we revealed two distinct textures involving topological defects in spherical caps of nematics governed by the reorganisation of the director field. In order to understand this surface induced restructuring of the director field, we performed optical simulations of the sessile droplets. Apart from the known discontinuous interfacial orientational transition we have also identified continuous director restructuring. Moreover we have also detected a double transition, involving a re-entrant behaviour.