Dispersion and distribution are different.... I am not into CNT-cement composites, but speaking from CNT-polymer composite experience, best way of improving distribution of CNT is by functionalizing CNT, lowering the viscosity of polymer solution and increasing the mixing time. 

While different, all the answers by our colleagues are correct. That is because CNTs are an heterogeneous material which requires a multi-instrumental characterization protocol able to describe its complexity and to support computational modelling, synthesis and application of CNT materials. In the past 4 years, we have developed a characterization protocol including TGA, UV-vis, Raman, and ATR-IR spectroscopies and dynamic light scattering for the characterization of CNTs and graphite derivatives in solution. Briefly,

1) sample of CNTs were extracted with 5.0 mL on an organic solvent (e.g., DMF, chlorobenzene, chloroform, N-methylpyrrolidone, methanol) by means of a sonication (Misonix 3000; power: 1 W/mL, pulse on: 3 s, pulse off: 3 s, time: 1 min) and a centrifugation (MR23i Jouan ultracentrifuge equipped with a SWM 180.5 swinging bucket rotor - Thermo electron corporation, 5 min @ 3000 rpm) procedure.

2) The supernatant was characterised by UV–vis-NIR absorption spectroscopy (Varian Cary5000, 280-1400 nm, SBW: 2 nm, scan rate: 300 nm/min). Given the extinction coefficient of CNTs, you can determine their concentration in solution (https://www.researchgate.net/publication/239631373_Optical_absorption_spectroscopy_for_determining_carbon_nanotube_concentration_in_solution).

3) A portion of the supernatant (500 microliters) was drop casted and annealed at 140 °C on platinum crubicle for TGA analysis (Q5000IR TGA - TA Instruments -

under air and nitrogen by an isotherm at 100 °C for 10 min followed by heating at 10 °C/min rate till 1000 °C) . After complete solvent removal, the TGA analysis will give you both the thermal behaviour of the CNTs and their effective concentration in solution (weight after solvent removal/500 microliters) (see: https://www.researchgate.net/publication/260566448_An_Insight_into_the_Functionalisation_of_Carbon_Nanotubes_by_Diazonium_Chemistry_Towards_a_Controlled_Decoration).

4) Another portion of the supernatant (100 microliters) was dropcasted on pre-cleaned glass micro slides (Corning) for ATR-IR (Nikolet 5700 spectrometer on a germanium window between 600 and 4000 cm-1 with a resolution of 0.5 cm-1) characterization. The resulting thin film was also characterised with an Invia Renishaw Raman microspectrometer (50 x objective) using the 633 nm line of a He–Ne laser at room temperature with a low laser power. (see comment above for Raman characterization).

5) Dynamic light scattering (DLS) was also used to obtain some information about the size distribution of CNTs in solution. It should be pointed out that DLS analysis is based on the assumption of spherical particle geometry; therefore, it cannot be used to obtain absolute size values for CNTs. Nevertheless, DLS allows comparing changes in the solvodynamic diameter of aggregates od CNTs prepared in different conditions (larger or smaller than...). DLS samples were obtained by diluting 50 microliters of the supernatant contianing CNTs to 2 mL of the same solvent. Then DLS measurements were performed with a Zetasizer Nano S (Malvern Instruments) at 20 °C setting 20 runs of 10 s for each measurement. (see: https://www.researchgate.net/publication/51466112_The_continuous-flow_cycloaddition_of_azomethine_ylides_to_carbon_nanotubes)

The combination of these five different and easily accessible techniques can indeed help you to "assess the dispersion level of CNTs within a solution" in terms of concentration (UV-vis and TGA), "size" of the aggregates (DLS), defects induced by the dispersion procedure (Raman and TGA). This protocol was indeed particular useful to us in comparing the results of different functionalization processes (see: https://www.researchgate.net/publication/261923267_Chemistry_of_Carbon_Nanotubes_in_Flow) and the behaviour of different carbon nanostructures (see: https://www.researchgate.net/publication/254261135_Synthesis_and_characterisation_of_a_trithiocarbonate_for_the_decoration_of_carbon_nanostructures?ev=prf_pub)

Moreover, if you prefer to rely on morphological analysis of the dropcasted material (NOT in solution!), we sometimes included the following techniques in our evaluation protocol:

6) AFM measurements were performed using a microscope Nanoscope IIIa, (Digital Instruments, Santa Barbara, CA) equipped with an extender electronics module in tapping mode in air at room temperature. Etched-silicon probes with a pyramidal-shape tip having a nominal curvature of 10 nm and a nominal internal angle of 35 were used. During the analysis, the cantilever, about 125 lm in length, with a nominal spring constant in the range of 20–100 Nm1, oscillated with its resonant frequency (about 330 kHz). Height images were recorded by collecting 512 · 512 points for each scan and maintaining the scan rate below 1 line per second. For AFM measurements, all samples were prepared by casting a 10–20 lL droplet on mica substrate and allowing it to dry.

7) X-ray photoelectron spectroscopy (XPS) was performed by using a VG Microtech ESCA 3000 Multilab spectrometer, equipped with a standard Al Ka excitation source

(hm = 1486.6 eV) and a nine-channeltrons detection system. The hemispherical analyser operated in the CAE mode, at a constant pass energy of 20 eV photoemission spectra were collected in an ultrahigh vacuum (UHV) chamber with a base pressure in the range of 10-8 Torr during data collection. The binding energy (BE) scale was calibrated by measuring C 1s peak (BE = 285.1 eV) from the surface contamination and the accuracy of the measure was ± 0.1 eV. Data analysis was performed by a nonlinear least square curve-fitting program (VGX900 software) using a properly weighted sum of Lorentzian and Gaussian component curves, after background subtraction according to Shirley and Sherwood.

Last comment: prolonged sonication in aqueous media in the presence of surfactant may lead to defects in the sp2 lattice of single-walled carbon nanotubes. You can check it in you sample by comparing the D/G ratio in the Raman spectra of pristine and dispersed CNTs and by looking at variation of in the thermal behaviour during thermogravimetric analysis. (see: https://www.researchgate.net/publication/259442648_Study_of_Photoluminescence_Properties_of_Single-Walled_Carbon_Nanotubes)

http://www.chimica.unipd.it/lab205/pubblica/

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Dear Sridhar Vadahanambi, Abderrahmane Benchirouf, Ayar Ayad Al-zubaidi, Patrizio Salice,

I just wanted to thank you a lot  for all the advices and information, am really appreciate your efforts.

Abderrahmane, the important aspects in my research are to study the mechanical and chemical behavior, and adequate mechanical performance of CNTs when introduced in a cement matrix and exposed to tensile strengths.

Best regards 

Salam 

Salam,

please be aware that quality of dispersion largely depends on starting material leading to huge differences.

http://appliedcolloidssurfactants.blogspot.de/2010/06/characterization-of-dispersion.html

Use ethanol as a disperson medium. and fix the sonication time.