- A novel family of silica-based mesoporous molecular sieveM41Swas synthesized by one of the Mobil research groups. Surfactant molecules were mixed with a silica solution, resulting in a regular array of uniform mesopores, 2−10 nm in diameter, capable of acting as a potential catalyst. The final long-range ordering of the silica−surfactant biphase composite material was found to be, depending on the reaction conditions, hexagonal, cubic, or lamellar. In this paper, we present an insight into the intermediate structures present in the solution during the synthesis of the hexagonal derivativeMCM41before long-range ordering is obtained. Cryo-transmission electron microscopy provides direct information on the primary building unitsclusters of elongated micelleswhich appear at the very early stage of the hexagonal mesophase formation, while small angle X-ray scattering is used for accurate structural analysis.