Growth of Mesoporous Silica Nanoparticles Monitored by Time-Resolved Small-Angle Neutron Scattering

Abstract

Since the first development of surfactant-templated mesoporous silicas, the underlying mechanisms behind the formation of their structures have been under debate. Here, for the first time, time-resolved small-angle neutron scattering (tr-SANS) is applied to study the complete formation of mesoporous silica nanoparticles. A distinct advantage of this technique is the ability to detect contributions from the whole system, enabling the visualization not only of particle genesis and growth but also the concurrent changes to the coexistent micelle population. In addition, using contrast-matching tr-SANS, it is possible to highlight the individual contributions from the silica and surfactant. An analysis of the data agrees well with the previously proposed "current bun" model describing particle growth: Condensing silica oligomers adsorb to micelles, reducing intermicellar repulsion and resulting in aggregation to form initial particle nuclei. From this point, the growth occurs in a cooperative manner, with condensing silica filling the gaps between further aggregating micelles. The mechanistic results are discussed with respect to different reaction conditions by changing either the concentration of the silica precursor or the temperature. In doing so the importance of in situ techniques is highlighted, in particular, tr-SANS, for mechanism elucidation in the broad field of materials science.

Nanocontainer‐Based Anticorrosive Coatings: Effect of the Container Size on the Self‐Healing Performance

“…For this reason, the scattering length density ρ sld , which is among others proportional to the electron density of the material, its molar mass and mass density, directly influence the scattering contrast. Therefore, the scattered intensity, which can be directly measured, relates to the Fourier transform of the scattering length density distribution in the sample 23, 24 . Figure shows a comparison of the scattering length densities ( ρ sld ) of the materials present in the studied samples.…”

Practical applications of small-angle neutron scattering

“…For soft dispersed media, the ability to measure the structure of solutions in situ, even in pressurized solvents 63 The ability to do this in real-time in situ is almost exclusive to small-angle scattering techniques, with SANS of particular benefit in studying the growth of materials around an organic template. 54 Given the number of materials for which this true,…”

A New Insight into Growth Mechanism and Kinetics of Mesoporous Silica Nanoparticles by in Situ Small Angle X-ray Scattering

“…[22][23] The mechanism of MSN growth has recently been studied through time-resolved small angle neutron scattering (SANS). 18,24 Even though the unique contrast variation provided by SANS can separate the scattering contributions from silica and surfactant phase, deuterated surfactants did not provide an adequate proxy for the normal synthesis of MSNs. 18 Due to much higher fluxes, synchrotron small angle X-ray scattering (SAXS) offers similar capabilities to SANS to make in-situ measurement but with greater sensitivity and can therefore reveal the growth of MSNs under real conditions without any special treatment of reaction ingredients.…”

“…The determination of reaction stage during MSN growth is complex and requires the simultaneous knowledge of a number of parameters. Multiple models are involved, in order to interpret those structural changes in terms of pore formation, particle growth and micelle reshaping 18. …”