exploring the self-assembly of mesoporous materials in the gas

Heinz Amenitsch
Insitute of Inorganic Chemistry, Graz University of Technology, Graz, Austria &
Austrian SAXS beamline, Outstation – Institute of Inorganic Chemistry, Graz University of
Technology, c/o Elettra-Sincrotrone Trieste, Basovizza (TS), Italy
Simultaneous Small and Wide Angle X-ray Scattering (SWAXS) is considered as standard
tool for the structural characterization of nanomaterials in all states of matter: solution, solid,
surfaces and gas phase. By combining it with results from other complementary methods like
TEM, SEM, NMR or Crystallography, detailed structural informations, from atomic lattice up
to the supramolecular envelope, can be obtained by performing simple and fast experiments
under in situ conditions1. Different methods of analysis such as interferometry, IR- or Raman
spectroscopy can also be coupled to the SWAXS setups, to perform parallel characterization
of the samples and achieve a better and deeper understanding e.g. of the kinetics of chemical
reactions, or of the mechanisms of growth and organization of nanostructured materials.
Evaporation induced self assembly (EISA)2 provides an attractive method for the synthesis of
mesostructured materials. A fast and economically interesting process for the production of
mesostructured particles is the spray-drying process of aerosol droplets, in which the
mesophase formation proceeds within a few seconds, but still, a high degree of control on the
final mesostructure is possible by applying suitable process parameters. Besides the chemical
composition, also the external conditions influencing the evaporation rate (e.g. temperature,
relative humidity) have been identified as key parameters for the resulting structure of the
mesophase 3 .
Most of the previous studies have been performed on the dried aerosol and provided
information on the effect of such parameters on the final structure e.g. 4 or at the end of the
evaporation chamber 4,5. For the in situ study, various setups were designed that enables the
gas-phase measurements during the evaporation process6. In an elongated evaporation vessel
temperature gradients from a starting temperature (e.g. 5°C) to final temperatures up to
400 °C can be applied within a few centimetres in the axial direction and provoke a fast
evaporation of the volatile components of the ESIA process. X-ray measurements can be
taken at steps along the temperature profile in the dryer tube and the self-assembly process
can be followed with SWAXS.
This presentation should give an overview of the different experiments starting from the exsitu deposition, in situ experiments of mesoporous materials and finally hierarchical assembly
of more complex structures.
1. Amenitsch,H. et al. First performance assessment of the small-angle X-ray scattering
beamline at ELETTRA. Journal of Synchrotron Radiation 5, 506-508 (1998).
2. Brinker,C.J., Lu,Y., Sellinger,A. & Fan,H. Evaporation-induced self-assembly:
Nanostructures made easy. Adv Mater 11, 579-585 (1999).
3. Boissiere,C., Grosso,D., Chaumonnot,A., Nicole,L. & Sanchez,C. Aerosol route to
functional nanostructured inorganic and hybrid porous materials. Adv Mater 23, 599-623
4. Shyjumon,I. et al. Mesostructured Silica Aerosol Particles: Comparison of Gas-Phase
and Powder Deposit X-ray Diffraction Data. Langmuir 27, 5542-5548 (2011).
5. Boissiere,C. et al. First in-situ SAXS studies of the mesostructuration of spherical silica
and titania particles during spray-drying process. Chemical Communications 9, 27982799 (2003).
6. Jungnikl,K. et al. Aerosol Flow Reactor with Controlled Temperature Gradient for In
Situ Gas-Phase X-Ray Experiments-Measurements of Evaporation-Induced SelfAssembly (EISA) in Aerosols. Aerosol Science and Technology 45, 805-810 (2011).