Characterisation of nano-assemblies inside mesopores using neutron scattering*

Abstract

Adsorption of molecular and nanoscale matter in mesoporous materials is important in filtration and chromatography as well as membrane processes. However, the morphology and distribution of self-assembled structures of adsorbate formed within nanoconfined environments is largely unknown. Small Angle Neutron Scattering (SANS) with porous matrix matching the neutron scattering length density of the solvent has the potential to provide detailed information on the self-assemblies formed in pore spaces. However, analysis of such SANS profiles remains a challenge. In this study, we extend the SANS analysis method previously developed by Findenegg and co-workers to include interparticle correlations, providing a qualitative characterisation of the adsorption state of surfactants and nanoparticles in the cylindrical pores of silica nanomaterials. We find that the pore filling fraction and the self-assembled state of the adsorbate governs the scattering profile. We apply the model to two materials namely, triethyleneglycol monohexyl ether (C₆E₃) surfactant and gold nanoparticles adsorbed in SBA-15 mesoporous silica. In contrast to the C₆E₃ system, Bragg scattering dominates the diffuse scattering in gold nanoparticle system, which we attribute to the immobile internal structure of the nanoparticles. This new SANS analysis method has potential to elucidate structures of soft matter nanoassemblies inside mesopores.

GRAPHICAL ABSTRACT

KEYWORDS:

• Adsorption
• neutron scattering
• mesoporous materials
• nanoparticles
• surfactants

Acknowledgements

Acknowledgment is made to the Donors of the American Chemical Society Petroleum Research Fund for partial support of this research. SANS experiments were supported by U.S. Department of Energy (DoE), Office of Science, Basic Energy Sciences, under EPSCoR Grant No. DE-SC0012432 with additional support from the Louisiana Board of Regents. Contributions to measurements and manuscript preparation by G. R. were supported by the DoE, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences and Biosciences Division. This research used resources at the High Flux Isotope Reactor and the Spallation Neutron Source, DOE Office of Science User Facilities operated by the Oak Ridge National Laboratory.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by American Chemical Society Petroleum Research Fund; Louisiana Board of Regents; U.S. Department of Energy [grant number DE-SC0012432].