Hydrophobic Intercalation of Layered Silicate Clays and Hierarchical Self-Assemblies via Platelet-Shape Directing

Most clay research in recent years has centered on the development of polymer/layered-silicate nanocomposites besides the conventional applications such as catalyst and adsorbents for organics. Recently, we have reported the hydrophobic modification of the naturally-occurring sodium montmorillonite clay (d spacing = 12 A) by exchanging with hydrophobic poly(oxypropylene)-diamine salts (POP-salt) to afford the space-enlarged silicates (d spacing up to 50-60 A). Owing to the geometrically plate-like shape and surface ionic charges, the organoclays enabled to self-assemble into rod-shape morphologies. For example, unique formation of lengthy rod (ca. 0.3 μm in diameter and up to 40 μm in length) was observed by using scanning electron microscopy (SEM). The self-assembling mechanism may involve the piling of the primary stack units by face-to-face and edge-to-edge alignments. The clay primary stacks intercalated by POP-salt and the hydrophilic analog of poly(oxyethylene)-diamine salts were observed by AFM.