Next Generation Models for Predicting the Shape of Solution-Grown Organic Crystals in the Presence of an Additive Michael F. Doherty, Chemical Engineering Department, University of California Santa Barbara Our research deals with the use of tailor-made additives as growth inhibitors for manipulating the shape of organic crystals. The most problematic shapes for many crystal growers are needles and flakes. We have focused our attention on needles because they are commonly encountered in pharmaceutical manufacturing. Para-aminobenzoic acid (PABA) is known to grow as needles from all solvents tested, therefore, it is not expected that its morphology can be altered by changing solvent. We have found that the tailor-made additive 4-propylbenzoic acid (4pBA) changes the crystal shape to a rod. We are currently using these and other data to develop models that are capable of predicting the effect of both solvents and additives on the shapes of organic crystals. PABA grown from pure water by quick cooling (scale bar = 1.0mm) – left figure. PABA grown from water plus 4pBA by quick cooling (scale bar = 1.5mm).