THE RELATIONSHIP BETWEEN YOUNG MODULUS OF ELASTICITY OF ORGANIC-SOLIDS AND THEIR MOLECULAR-STRUCTURE

Young's modulus of elasticity of organic drugs and excipients as determined by 3-point beam bending can be predicted from cohesive energy density. However, the moduli are lower than expected from theory due to specimen effects or to temperature differences between the theoretical treatment and measurements made at room temperature (i.e., compacted beams, 3-point beam bending). When experimentally determined single crystal elastic constants are used to calculate Young's modulus for a number of molecular solids, agreement between experiment and theory is improved. For Aspirin, there was good agreement between the lattice dynamic approach, the theoretical equation based on cohesive energy density and experimental measurements based on the flexure of compacted beams.