Self-Organized Assembly of Copper Oxalate Nanocrystals

Copper oxalate has been precipitated in water and acetone. Raman spectroscopy is performed to validate the chemical composition of the obtained powders. Aqueous precipitation has led to micrometer-scaled agglomerates, whereas acetone precipitation has led to nanorods showing a two-dimensional (2D) self-organization when deposited on a Si substrate. Scanning electron microscopy (SEM) and atomic force microscopy (AFM.) show an anisotropic structure of the agglomerates with two kinds of faces. Nanoplatelets with self-assembly abilities are also detected in the copper oxalate aqueous suspension. These observations reveal a supracrystal line self-assembly process leading to micrometer-scaled three-dimensional (3D) superstructures. AFM measurements on nanoplatelets and nanorods are correlated to X-ray diffraction results. A kinetic study carried out by SEM highlights four main steps in the 3D self-assembly process. Each step corresponds to a specific assembly speed ratio between the two directions that define the superstructures. Additives like hydroxypropylmethylcellulose (HPMC) and glycerin modify this speed ratio and therefore allow the shape of the supracrystals to be controlled.