Anisotropic surface properties and wettability of disperse dye single crystal

The anisotropic surface properties of macroscopic single crystals of C.I. Disperse Yellow 114 have been investigated. The changing contact angles between the facets of the crystal and water by drop contact angle measurements are associated with chemical heterogeneities present on the surfaces. The surface free energy on four indexed crystal facets, calculated by using Wu's method, indicated the dispersive components of the surface energies for the different crystal facets are close to each other, while its polar components are quite distinct. The anisotropic nature of the physical properties of the dye crystals is attributed to the functional groups and their densities on the individual crystal surfaces. Moreover, the surface hydrophobicity of compressed discs of milled crystalline dye powder was increased in comparison to that of crystal facets to such an extent that it is very difficult to predict the crystal surface properties from the compressed discs. (C) 2012 Elsevier Ltd. All rights reserved.