Prominence of the Instability of a Stabilizing Agent in the Changes in Physical State of a Hybrid Nanomaterial

Abstract

Shaping ability of hybrid nanomaterials is a key point for their further use in devices. It is therefore crucial to control it. To this end, it is necessary that the macroscopic properties of the material remain constant over time. Here, we evidence by multinuclear Magic‐Angle Spinning Nuclear Magnetic Resonance spectroscopic study including 17O isotope exchange that for a ZnO‐alkylamine hybrid material, the partial carbonation of amine into ammonium carbamate molecules is behind the conversion from highly viscous liquid to a powdery solid when exposed to air. This carbonation induces modification and reorganization of the organic shell around the nanocrystals and affects significantly the macroscopic properties of the material such as it physical state, its solubility and colloidal stability. This study, straightforwardly extendable, highlights that the nature of the functional chemical group allowing connecting the stabilizing agent (SA) to the surface of the nanoparticles is of tremendous importance especially if the SA is reactive with molecules present in the environment.

Mechanistic insights into the anisotropic growth of ZnO nanoparticles deciphered through 2D size plots and multivariate analysis

“…The isotropic NPs are consumed to the benefit of the length of the rods that increases concomitantly. 29 …”

“…Whereas initial nucleation reaction is fast (after 1 minute solutions became luminescent which demonstrate the formation of ZnO NPs), growth mechanism seems to be stopped only after 5 days. This halt in the growth is certainly due to the partial carbonation of alkylamines into ammonium carbamates which, as we have recently shown, 29 leads to a complete modification of the organic stabilizing agents on the surface of the NPs. When NPs are only stabilized by alkylamines, these latter are localized only along the lateral faces leaving the basal faces accessible for growth by oriented attachment, [31][32][33] whereas in the presence of ammonium carbamates, these are located both on the lateral and the basal faces with a very strong affinity preventing the growth from continuing.…”

“…The isotropic NPs are consumed to the benefit of the length of the rods that increases concomitantly. 29 Furthermore, C. Ribeiro et al suggest that growth of nanorods through an oriented attachments mechanism can be described as a "polymerization" reaction. 30 In that case and following various simplifications, the number of NPs, x max , which have undergone a coalescence process leading to a nanorod should follow the equation: where t is the time of reaction,  is a constant parameter between 0 and 1, k 0 a kinetic constant and [S] 0 the initial concentration of active surfaces on the isotropic NPs (i.e.…”

“…When NPs are only stabilized by alkylamines, these latter are localized only along the lateral faces leaving the basal faces accessible for growth by oriented attachment, [31][32][33] whereas in the presence of ammonium carbamates, these are located both on the lateral and the basal faces with a very strong affinity preventing the growth from continuing. 29 Fig. 2 TEM images and associated 2D size plots (left).…”

Anisotropic growth of ZnO nanoparticles driven by the structure of amine surfactants: the role of surface dynamics in nanocrystal growth

“…From a geometrical perspective (Scheme 1), multiple H-bonding reduce the mobility of primary amines at the surface of the NC. This additional network mainly localizes along the lateral faces of the NCs (left), 91,92 and is directly responsible for the 1D anisotropic growth of ZnO NCs. Conversely, the secondary amine surfactant does not form such hydrogen bonding network, or to a much limited extent (right).…”