DOES MICROGRAVITY INFLUENCE SELF-ASSEMBLY

The templated syntheses of TMA(2)Sn(3)S(7) and TBA(2)Sn(4)S(9) (where TMA is tetramethylammonium and TEA is n-tetrabutylammonium) microporou s layered tin(Iv) sulfides have been carried out under both microgravi ty (mu G) and earth (1G) conditions in order to elucidate the influenc e of gravity on the self-assembly and crystal-growth processes of this class of materials. The mu G experiments were conducted on board the May 1996 Endeavour STS-77 NASA space-shuttle flight. It was determined that the long-range ordering of the porous layers and the population of defects but not the short-range ordering within the layers is influ enced by gravity. Bulk and surface crystallinity, smoothness of crysta l faces, optical quality, crystal habits, registry of the porous layer s, and accessible void volume to adsorbates were found to be improved in the space-grown crystals. This is probably because the forces assoc iated with the organization of the porous layers are expected to be we ak and sensitive to the elimination of buoyancy-driven convective flow s and Stokes sedimentation effects in a microgravity environment, One can draw an analogy to the weak forces between protein macromolecules and the established effect of microgravity on improving the diffractio n quality of crystals harvested in space.