Self-Assembly of Diacid Molecules: A Theoretical Approach of Molecular Interactions

Abstract

Dicarboxylic acids have been recently found to provide a significant improvement of the mechanical properties of hard materials such as bitumen when added at low concentration. To understand such properties, periodic DFT calculations combined with empirical van der Waals corrections have been performed on crystals of dicarboxylic acid molecules with various chain lengths. Our calculations allow us to understand the interactions governing the cohesive energy of the crystal and to qualitatively correlate diacid transition phase properties (fusion, vaporization, and sublimation) to their behavior when mixed in bitumen. The molecules are distorted because of structural constraints in the crystal packing and that distortion is found to be larger for odd diacids than for even diacids, explaining the usual odd−even alternation of their properties related to the solid state. In particular, the relative fusion temperature of diacids as a function of chain length is dominated by distortion effects. In contrast, mos...