Self-assembly of copper succinate nanoparticles to form anisotropic mesostructures

Uniform cylindrical rods of copper succinate dihydrate of several microns in length and 200 nm in diameter were obtained by the reverse micellar (microemulsion) method at room temperature using CTAB as the surfactant. The rod-like structures are formed by an ordered assembly of spherical particles of 4-5 nm, which is facilitated by water molecules. The copper succinate particles, in the absence of the microemulsion or surfactant, show only spherical geometry, while in the presence of the surfactant, thicker rods (compared to as obtained by reverse micellar method) of varying length were obtained. The formation of the rod-like structure is driven by the permanent dipole moment of the succinate ion, which leads to the oriented attachment of the nanoparticles in the presence of the surfactant. A new phase (anhydrous copper succinate) is obtained upon heating the dihydrate at 75 degrees C, which shows branched and corrugated rods assembled from a random arrangement of nanoparticles. The water molecules appear to control the morphology of the rods giving smooth rods (ordered arrangement of nanoparticles) for the dihydrate while branched or disrupted rods with random arrangement of nanoparticles are obtained for the anhydrous phase. The chain length of the dicarboxylic acid (ligand) appears to have a role in controlling the aspect ratio of these anisotropic mesostructures. The ability to generate suitable conditions for self assembly into ordered nanostructures and to control the anisotropy would lead us towards a proper design of nanodevices.