Surfactants for dispersion of carbon nanotubes applied in soil stabilization

The discovery of the unique properties of carbon nanotubes (CNT) did grow interest to its application in nanocomposites, for a wide variety of purposes. However, the greatest challenge for its application is associated with the natural tendency to aggregate, resulting in the loss of its beneficial properties. To overcome this problem it is common the use of surfactants and/or ultrasonic energy to promote their dispersion in suspension. This work is focused on the influence of surfactants’ properties on the dispersion of carbon nanotubes and on the influence of the quality of the dispersions on the mechanical properties of stabilized soil. Two surfactants (Glycerox and Amber 4001 differing in molecular weight and charge) were fully characterized, followed by the study of which surfactant concentrations were more efficient on the dispersion of the CNTs. The characterization methods were based on light scattering techniques: Dynamic Light Scattering (DLS) for the hydrodynamic diameter and Static Light Scattering (SLS) for the molecular weight. Suspensions of CNTs were prepared in solutions of the aforementioned surfactants, with different concentrations, and further dispersion was promoted using ultra-sounds (20 kHz during 5 min). The dispersions of CNTs in these two surfactants were then fully characterized using again DLS. Finally, the dispersions of carbon nanotubes were added to the main agent responsible for soil stabilization, the binder (Portland cement type I 42.5R), and the mechanical behavior of the new composite material was studied by unconfined compression strength (UCS) tests. The results of the UCS tests led to conclude that the introduction of CNTs in the binder can have huge impact on the mechanical properties of the stabilized soil. Furthermore, the quality of the dispersion of CNTs has got a very high impact on the performance achieved. It was verified an improvement up to 77% on the compressive strength of the material and 155% on Young's modulus, referred to the reference test where no carbon nanotubes nor surfactant were added, fundamentally dependent on surfactant type and concentration used.

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