Quantified analysis of 2D dispersion of carbon nanotubes in hardened cement composite using confocal Raman microspectroscopy

Dispersion of carbon nanotubes (CNTs) is the critical factor affecting the performance of nanocomposites; however, the quality of CNT dispersion could be indirectly understood due to the limitations of evaluation methods of the dispersion. This study aimed to visualize the macroscopic spatial distribution of CNTs in an as-is hardened cement matrix for the quantification of dispersion. Using a confocal Raman microspectroscopy equipped with an optical microscope, the major phases in cement, hydrates, and CNTs were identified from their characteristic Raman signals to construct the definitive phase map. The dispersion efficiency and heterogeneity were defined to quantify the fraction of CNT-affected region and the unevenness of CNT distribution. The experimental results demonstrate the importance of a well-dispersed stable state in CNT suspension and suggest that it is possible to evaluate the effectiveness of ultrasonication with superplasticizers that have been frequently adopted as a dispersion technique in hardened cement composites.