Ordered structures in carboxymethylcellulose-cationic surfactants-copper ions precipitated phases: in situ formation of copper nanoparticles.

Small-angle X-ray scattering has been used to investigate the nanostructures in precipitated phases of carboxymethylcellulose/oppositely charged C(n)TAB surfactants mixtures in interaction with bivalent copper ions. In copper-free precipitates, a transition from a 2D hexagonal phase H(I) to a micellar cubic surfactant structure Pm3n was found on increasing the polymer concentration (n = 14, 16). By addition of small amounts of copper ions, the internal structure also changes from H(I) to Pm3n cubic and finally turns into a less-ordered phase. The concentration at which this transition occurs strongly depends on the surfactant tail length. The presence of copper ions in the precipitated phase leads at the same time to a disorganization of the surfactant micelles' order and to the formation of a lamellar ordering, revealed by the presence of additional diffraction peaks above 10 mM copper. We used the polymer/surfactant networks as template systems, controlled by the copper ion content, for preparing embedded copper nanoparticles via in situ reduction of copper sulfate by sodium borohydride. The zerovalent copper particles formed in the cubic lattice are well-defined in size (less than 10 nm) and have a homogeneous distribution, whereas they are very polydisperse when the reduction is performed in the unorganized phase because the lack of order in the matrix does not protect them from aggregation.