Nanoparticle size controls aggregation in lamellar nonionic surfactant mesophase

Ferrihydrite nanoparticles entrapped in shear-induced multilamellar vesicles

HYPOTHESIS

Ferrihydrite (Fh) nanoparticles are receiving considerable scientific interest due to their large reactive surface areas, crystalline structures, and nanoparticle morphology. They are of great importance in biogeochemical processes and have the ability to sequester hazardous and toxic substances. Here, the working hypothesis was to entrap fractal-like Fh nanoparticles, with a radius of gyration of 6.2 nm and a primary building block of polydisperse spheres with a radius of 0.8 nm, in a shear-induced multilamellar vesicle (MLV) state using a 40 wt% polyethylene glycol dodecyl ether surfactant.

EXPERIMENTS

Small- and Wide- Angle X-ray scattering revealed the equilibrium state of the non-ionic planar lamellar phase, the Fh dispersion, and their mixture. The MLV state was induced by using a shear flow in a Taylor-Couette geometry of a rheometer.

FINDINGS

The nonionic surfactant initially exhibited a lamellar gel phase with two distinct d-spacings of 11.0 and 9.7 nm, which collapsed into the MLV state under shear flow. The Fh nanoparticles induced bilayer attraction by suppressing lamellar layer undulations, decreasing the d-spacing. These results are helpful in the understanding of the relationship between nanoparticle size and nanoparticle-bilayers interactions and provides insight on Fh encapsulations in a kinetically stable MLVs state.

Preparation of Novel Mesoporous Silica Using a Self-Assembled Graphene Oxide Template

Novel mesoporous silicas rolled with silica sheets with 2D regular spacing were prepared using a self-assembled graphene oxide (GO) template formed by mixing GO with Pluronic123 (P123). Self-assembled GO templated mesoporous silicas (SGT-PMS) showed well-developed X-ray diffraction peaks with d-spacings of 9.8–10.8 nm depending on the amount of GO, indicating mesoporous structures. The specific surface areas increased from 603.8 to 861.2 m²g⁻¹ on adding GO. The pore size distribution was in the range 5.1–5.8 nm and pore volume in the range 0.80–0.99 m³g⁻¹. The SEM images of SGT-PMS showed irregular elliptical particles with various sizes. TEM images showed that the cross section of SGT-PMS particles comprises a roll of silica sheets with 2D regular spacing. The pore walls of SGT-PMS are firmer and thicker than those for PMS without GO as indicated by the corresponding intensities of Q³ and Q⁴ signals. These results were explained well by the self-assembled GO templating mechanism.

Preparation of Mesoporous Silica by Nonionic Surfactant Micelle-Templated Gelation of Na2SiO3 and H2SiF6 and Application as a Catalyst Carrier for the Partial Oxidation of CH4

Mesoporous silica (MSPN12) was prepared by nonionic surfactant micelle–templated gelation of sodium silicate (Na₂SiO₃) and fluorosilicic acid (H₂SiF₆) in aqueous solution, characterized by a range of instrumental techniques, and tested as a support for Ni and Rh catalysts in the partial oxidation of methane (POM). Calcined and sintered MSPN12 exhibited well-defined d_00l-spacings (3.5–4.39 nm), narrow pore distributions (2.4–3.1 nm), and large specific surface areas (552–1,246 m² g⁻¹), and was found to be highly thermally stable. Microscopic imaging revealed that MSPN12 comprised spherical particles with a uniform diameter of ~0.7 µm, with each particle featuring firm and regular honeycomb-type pores. MSPN12-loaded Ni and Rh maintained stable POM activity at 700 °C during almost 100 h on stream, which were comparable to those for the commercial Rh(5)/Al₂O₃ catalyst in terms of methane conversion and H₂ formation selectivity. Thus, the combination of structural stability and favorable physicochemical properties resulted in good POM performance.

Tuning the structure, thermal stability and rheological properties of liquid crystal phases via the addition of silica nanoparticles

The effects of adding silica nanoparticles of varying size and surface chemistry to a liquid crystal system were analysed using small-angle scattering and polarising light microscopy, with varying temperature and applied shear.

Structural and rheological changes of lamellar liquid crystals as a result of compositional changes and added silica nanoparticles

Lamellar liquid crystals comprising oil, water and surfactant(s) were formulated and analysed in order to examine how these materials responded to the inclusion of inorganic nanoparticles, in terms of their structural and rheological characteristics. Lamellar phases were formed from mixtures of water, para-xylene and Triton X-100, and analysis was performed via small-angle neutron scattering (SANS), polarising light microscopy (PLM), and amplitude and viscosity sweeps. The partial replacement of Triton X-100 with oleic acid appeared to cause an increase in bilayer thickness, attributed to less efficient packing of the different molecules. Addition of oleic acid also appeared to cause both a loss in lamellar repeat ordering, attributed to heterogeneity of the bilayers, and a rise in long range order, potentially caused by the stiffer bilayers. Adding silica nanoparticles of different size and surface chemistry caused a stiffening of the samples at the expense of a longer-range lamellar repeat order. This strengthening is attributed to aggregation at the domain boundaries, and it was found that hydrophobic particles tended to form stronger aggregates while for larger particles (20 nm as opposed to 10 nm) aggregation was apparently reversible. These results give a more comprehensive understanding of how to reliably control the structural and rheological properties of lamellar liquid crystals, and emphasise the importance of the size and surface chemistry of any inclusions, for applications in cosmetics, drug delivery, and microfluidics.