SOLVENT EFFECT ON THE ROUGHENING TRANSITION AND WETTING OF N-PARAFFINCRYSTALS

The solubility parameters, roughening temperatures and edge free energ ies have been measured as a function of temperature and interpreted fo r n-C23H48 and n-C25H52 crystals. The crystals have been grown from so lutions consisting of n-hexane and toluene mixtures. The dissolution e nthalpy is used to determine the strongest bond in the bulk of the cry stal Phi(str)(bulk) and the roughening temperature is used to determin e the strongest bond in the crystalline interface Phi(str)(int). The r atio of these two bonds is called the wetting kappa of the crystalline interface. It turns out that the solutions containing mixtures of n-h exane and toluene behave according to a regular solution, which follow s directly from thermodynamics with the use of a mean field approach. The strongest bond in the bulk of the crystal has the same dependence on the composition of the solution as the dissolution enthalpy. In con trast with this, the strongest bond in the interface stays approximate ly constant and, therefore, the dependence of the wetting re on the co mposition of the solution follows that of the enthalpy of dissolution. (C) 1998 Elsevier Science B.V. All rights reserved.