Colloidal nanoparticle suspensions

In academic research as well as applied work with nanoparticles, the particles are typically handled as colloidal dispersions. Hydrophobic nanoparticles, such as carbon nanotubes or graphene flakes, are typically dispersed in a water-based continuous phase with the help of surfactants (or amphiphiles) that adsorb at the particle-solvent interface and stabilize the system from particle aggregation [1]. Since these systems are almost always thermodynamically unstable such kinetic stabilization is absolutely essential for being able to work with these particles in an efficient way.

A carbon nanotube dispersion that allows macroscopic organization of the tubes by shearing.

Although the surfactant-based stabilization is a well established approach to achieve nanoparticle colloids there are actually many issues that have not been well investigated. In our research on this topic, which is a long-term research thrust together with the LC Nano Lab of Prof. Giusy Scalia, we have taken some quite original directions to improving nanoparticle dispersion quality, stability and processability. We also take a special interest in dispersions with high surfactant concentration, required for liquid crystal formation by the surfactant solution. A liquid crystalline host phase provides many interesting benefits but it also poses some unique challenges. The general lack of studies of colloidal suspensions at high surfactant concentrations leaves many interesting questions to be addressed, of applied as well as fundamental physicochemical interest.


A dispersion with well exfoliated carbon nanotubes forms a physical gel at the relatively low nanotube concentration of 3 wt.-%.

Some of our key publications on the topic are the following:

• Carbon nanotubes in liquid crystals (Review article)
  Jan P. F. Lagerwall, Giusy Scalia
  J. Mater. Chem. 18, 25, pp. 2890-2898 (2008), special issue on ‘Liquid crystals beyond display applications’.
• Filament formation in carbon nanotube-doped lyotropic liquid crystals
  Stefan Schymura, Sarah Dölle, Jun Yamamoto and Jan Lagerwall
  Soft Matter, 7, 6, 2663 - 2667 (2011)
• Tailor-designed polyphilic promotors for stabilizing dispersions of carbon nanotubes in liquid crystals
  Martin Kühnast, Carsten Tschierske and Jan Lagerwall
  Chem. Commun., 46, pp. 6989-6991 (2010)
• Towards Efficient Dispersion of Carbon Nanotubes in Thermotropic Liquid Crystals
  Stefan Schymura, Martin Kühnast, Vanessa Lutz, Stefan Jagiella, Ursula Dettlaff-Weglikowska, Siegmar Roth, Frank Giesselmann, Carsten Tschierske, Giusy Scalia, and Jan Lagerwall
  Adv. Funct. Mater., 20, 19, pp. 3350–3357 (2010)
• Macroscopic-scale carbon nanotube alignment via self-assembly in lyotropic liquid crystals
  S. Schymura, E. Enz, S. Roth, G. Scalia, J.P.F. Lagerwall
  Synth. Met., 159, 21-22, pp. 2177-2179 (2009)
• Spontaneous macroscopic carbon nanotube alignment via colloidal suspension in
  hexagonal columnar lyotropic liquid crystals
  G. Scalia, C. von Bühler, C. Hägele, S. Roth, F. Giesselmann, and J.P.F. Lagerwall
  Soft Matter, 4, 3, pp. 570-576 (2008)
• Nanotube alignment using lyotropic liquid crystals
  Jan P. F. Lagerwall, Giusy Scalia, Miroslav Haluska, Ursula Dettlaff-Weglikowska, Siegmar Roth, Frank Giesselmann
  Adv. Mater. 19, 3, pp. 359-364 (2007)

References

[1] H. Wang, ‘Dispersing carbon nanotubes using surfactants’, Curr. Opin. Colloid Interface Sci., 14, pp. 364-371 (2009)
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