Polymorphism in aspirin

Abstract

Abstract In order to clarify the misconceptions and uncertainties concerning the polymorphism of aspirin a study using both Bragg and diffuse X-ray scattering was undertaken. A MC simulation model for aspirin has been developed which includes occupational disorder and SRO as well as the effects of local strain. By adjusting occupancy variables the model can be made to describe a whole range of structures varying from the pure form I to the pure form II structure. For all intermediate structures it is necessary to consider strain at the interfaces. The modeling shows that form II has a structure quite distinct from that of form I but contains plate-like inclusions that consist of thin layers of the form I structure.