Surface-induced nucleation strategies: seeking symmetries between self-assembly of heteronucleants and crystals

The present paper presents the application of surfaces having defined and controlled attributes as heteronucleants for the crystallization of a model pharmaceutical molecule. The synthesis of the substrate was optimized in order to relate surface features to the crystallization outcome. Extremely flat and topographically uniform glass supports bearing amino and thiol head groups were successfully synthesized and characterized by means of contact angle, AFM and XPS analyses. Such surfaces were then used as supports for aspirin (ASA) crystallization in order to investigate their influence on nucleation kinetics. Compared to untreated glass, amino-functionalized glass was dramatically nucleation-active, whereas thiol-functionalized supports strongly repressed ASA heterogeneous nucleation. The promoting or inhibiting action towards the stabilization of ASA nuclei on a functionalized surface and their successive growth into crystals was therefore related to the chemistry of exposed head groups.