The crystal habits and length–breadth aspect ratios of sulfathiazole crystals produced by the 11 pure single solvents and 13 solvent mixtures of acetonitrile, n-propanol, and water by cooling are shown in Figures 10 and 11, respectively. In general, Form I possessed a needle-like morphology. Form II had a cuboid morphology. The morphology of Form III was a truncated hexagon and Form IV had a plate-like hexagonal morphology (9). If crystal habits alone are used as a visual guide, the major phases grown from the 11 pure single solvents were: Form I in MEK, acetone, benzyl alcohol, acetonitrile, and n-propanol; Form III in THF, DMF, ethanol, DMSO, and water; and Form IV in methanol. Clearly, the observation that Form I appeared with the same crystal habit from more than one solvent suggested that none of the available solvent–surface interactions could inhibit the addition of sulfathiazole molecules to the {010} face (9). A similar conclusion could be drawn for Form III and its fast-growing {110} face (9).

Figure 8

Figure 9

Figure 10