Cationic surfactants, didodecyldimethylammonium bromide (DDAB), 1-dodecyl-3-methylimidazolium bromide ([C(12)mim]Br) and DDAB/[C(12)mim]Br mixture were used to induce the formation of calcium carbonate (CaCO(3)) crystals at ambient temperature. The obtained CaCO(3) particles were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM). X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The morphologies of CaCO(3) crystals changed from laminated cube to sphericity and string shape with the increase of DDAB and [C(12)mim]Br concentration, respectively. Flower-shaped CaCO(3) crystals were synthesized in the mixed DDAB/[C(12)mim]Br system. More importantly, it was found that the complete conversion from calcite to vaterite was achieved at room temperature only through changing DDAB concentration. The regulations of DDAB and [C(12)mim]Br to CaCO(3) crystals have been compared with that of dodecyltrimethylammonium bromide (DTAB) in our previous work and possible mechanisms have been proposed. It is shown that the cationic surfactants can control the crystallization of CaCO(3) and the number of hydrophobic alkyl chains of cationic surfactants might be more effective in modulating the crystallization of vaterite than the head groups. (C) 2011 Elsevier B.V. All rights reserved.