To disperse carbon nanotubes (CNTs) Cheap Tubes recommend the following process.
Using the SONICS VCX750 ultrasonic equipment, from Sonics & Materials, Inc. or equivalent, Cheap Tubes Inc. find that adding the dispersant into the solution can accelerate the dispersion effect. The reagent polyvinylpyrrolidone (PVP) is a good dispersion agent. Some people like to use the reagent Sodium dodecyl benzene sulfonate, but we find that the PVP is a better dispersing reagent.
The solution is composed of CNTs, PVP, and water, in the proportions of 10 parts CNTs: ~1-2 parts PVP: 2,000 parts water. The required sonication time is ~2 to 8 minutes with an interruption of 10 seconds every 30 seconds. You must prolong the sonication time accordingly, if the power of your ultrasonic equipment is less than that of the SONICS VCX750 unit.
It should be noted that our OH and COOH functionalized CNTs can usually be readily dispersed in DI water and a brief sonication step. This dispersion is very stable and the CNTs can remain in solution for weeks or months.
Functionalization
Pristine nanotubes are unfortunately insoluble in many liquids such as water, polymer resins, and most solvents. Thus they are difficult to evenly disperse in a liquid matrix such as epoxies and other polymers. This complicates efforts to utilize the nanotubes’ outstanding physical properties in the manufacture of composite materials, as well as in other practical applications which require preparation of uniform mixtures of CNTs with many different organic, inorganic, and polymeric materials.
To make nanotubes more easily dispersible in liquids, it is necessary to physically or chemically attach certain molecules, or functional groups, to their smooth sidewalls without significantly changing the nanotubes’ desirable properties. This process is called functionalization. The production of robust composite materials requires strong covalent chemical bonding between the filler particles and the polymer matrix, rather than the much weaker van der Waals physical bonds which occur if the CNTs are not properly functionalized.
Functionalization Methods
Functionalization methods such as chopping, oxidation, and “wrapping” of the CNTs in certain polymers can create more active bonding sites on the surface of the nanotubes. For biological uses, CNTs can be functionalized by attaching biological molecules, such as lipids, proteins, biotins, etc. to them. Then they can usefully mimic certain biological functions, such as protein adsorption, and bind to DNA and drug molecules. This would enable medially and commercially significant applications such as gene therapy and drug delivery. In biochemical and chemical applications such as the development of very specific biosensors, molecules such as carboxylic acid (COOH), poly m-aminobenzoic sulfonic acid (PABS), polyimide, and polyvinyl alcohol (PVA) have been used to functionalize CNTs, as have amino acid derivatives, halogens, and compounds. Some types of functionalized CNTs are soluble in water and other highly polar, aqueous solvents.
This information has been sourced, reviewed and adapted from materials provided by Cheap Tubes Inc.
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