CheapTubes has been supplying nanomaterials to consumers for over a decade and possess a wide range of nanomaterials, including carbon nanotubes (CNTs), graphene (and its various derivatives), amongst various other nanomaterials. CheapTubes has just added another product to its arsenal, which has been realized through a recent patent, it is a graphene-based surfactant nanosheet that can disperse a wide range of other nanomaterials.
Who Are CheapTubes?
Founded by Mike Foley in 2005, and based in Vermont, USA, CheapTubes has been supplying nanomaterials for 13 years now and has supplied nanomaterials to over 5000 customers worldwide. Some of their notable customers include 3M, MIT, NASA, Harvard University and the U.S. Army.
CheapTubes started out as a supplier of some of the cheapest CNTs on the market (back when they were very expensive), hence the name, and have since expanded out into graphene, boron nitride, functional inks, nanowires, fullerenes, and most recently, tunable surfactant nanosheets – i.e. Flexiphene.
The recent Flexiphene patent from CheapTubes, has been officially assigned to its sister (IP holding) company – CTI Materials.
Photo by jhuang / CC BY 2.0
What Is Flexiphene?
Flexiphene is an amphiphilic and tunable surfactant sheet that can be used to efficiently disperse a wide range of nanomaterials, including graphene, CNTs and nanowires. It is an easy solution for those who need to disperse nanomaterials into a certain medium (even if they are not traditionally dissolvable in that solvent).
Flexiphene sheets have a graphene-based backbone, with oxygen-rich functional groups on the edges and basal plane. These can be used to disperse various nanomaterials into both aqueous and organic solvents (as well as solid hosts) and can tune the dispersion by changing the pH, size of the surfactant sheet and the degree of reduction on the sheet.
Flexiphene can be used for a wide range of applications, including general dispersions, emulsions, membranes, sensors, monolayers-Langmuir-Blodgett films, conductive and transparent-conductive films and electrodes, to name a few.
How Flexiphene Works
Flexiphene works by specifically tuning the degree of amphiphilicity in the sheets so that the desired nanomaterial becomes dispersed into a choice of solvent/host. Flexiphene possesses distinct amphiphilic regions, with the edges and the functional groups in the basal plane being hydrophilic while the rest of the sheet is hydrophobic.
Flexiphene acts in a similar manner to ionic type surfactants, so changing the pH has a big effect on the Flexiphene sheets because it changes the degree of ionization on the carboxylic acid groups (–COOH). Therefore, the use of higher pH values increases the amount of edge charges, which increases the hydrophilicity of the sheet.
Aside from tuning the pH to change the amphiphilicity, the degree of hydrophilicity is also highly dependent upon the size of the sheet, with smaller sheets possessing a higher hydrophilicity because of a higher edge-to-area ratio.
Photo by tliu / CC BY 2.0
The final way that Flexiphene can be tuned is through the degree of reduction on the Flexiphene sheet. This can be done by removing some of the oxygen-based functional groups from the edges and basal plane of the Flexiphene sheet. This in turn reduces the amount and size of the hydrophilic nanographene regions making them more conductive. The charge density of the Flexiphene sheets will also vary depending on the pH values, sheet size and degree of reduction.
The Properties and Specific Workings of Flexiphene
The most obvious, and vital, property of these Flexiphene sheets is their amphiphilicity. Moreover, it is the ease and many ways in which the sheets can be tuned that make it an ideal material for dispersing many different materials.
Flexiphene is a highly adherent material that can stabilize a solid-liquid interface by wrapping itself around a nanomaterial of interest, even if they are conventionally insoluble. This is achieved through a combination of its large lateral dimensionality, multiple adhesion sites and π-conjugated nanopatches in the basal plane. Moreover, in its highly reduced form, Flexiphene can act as a particle separator and stop nanoparticles from agglomerating.
How Flexiphene interacts with the solvent and nanomaterial of interest depends on both constituents. For aqueous based solvents, the Flexiphene sheet will adhere to the surface of water, whereas in oil-water solvent mixtures, the sheet will stabilize the interface between the two immiscible regions and form a Pickering emulsion. This approach is also capable of dispersing other π-conjugated materials, such as organic semiconductors and conducting polymers.
The amphiphilic nature of Flexiphene also enables it to be solution-processed for use in spin coating, drop casting, spraying, and dip coating methods. As well as coating methods, Flexiphene can be employed in nanoparticle assembly methods and can be used to create a defined layer thicknesses, including monolayers, without any occurrence of wrinkling, crumpling or non-uniformities across the surface.
Some other properties include its ability to form pillars in hybrid structures, no by-product formation, and reducing the number of induced defects when preparing a material and/or dispersion. One final property of Flexiphene is its very high aspect ratio, which enables it to form a liquid crystal phase. In its liquid crystal form, Flexiphene also exhibits an optical birefringence and has an anisotopic light scattering effect.
Why Use Flexiphene?
Dispersion is critical if you want to take full advantage of a nanoscale additive’s properties. Traditionally, surfactants, or highly functionalized materials, have been used with mixed results.
The problem with surfactants is that they are very difficult to remove and usually leave residues behind. They are beneficial for dispersing a species, but their residues interfere with their conductive and mechanical properties. Some surfactants, like PVP, wrap the nanomaterials and are harder to remove.
Researchers often try to remove them, which is very difficult and can add additional processing steps and add defects to the films or coatings. One method to remove surfactants involves multiple solvent washes and a gas treatment.
The problem with functionalized materials is that they are often damaged by aggressive functionalization, which does promote dispersion, but also reduces the nanomaterial’s conductive and mechanical properties.
Flexiphene puts the functionality where it belongs, i.e. on the dispersant, and effectively disperses non-functionalized nanomaterials, thus preserving the nanomaterial’s unique properties. Colloidal dispersions of SWCNTs in deionized (DI) Water are easily produced with Flexiphene. CTI has produced Flexiphene/SWCNT dispersions which measured -70 eV with dynamic light scattering, 9 days after sonication – thus showcasing that they can be colloidally dispersed in DI Water.
Sources and Further Reading
- CheapTubes: https://www.cheaptubes.com/product-category/flexiphene-surfactant-sheets/
- “Graphene oxide as surfactant sheets”- Huang J. et al, Pure and Applied Chemistry, 2011, DOI: 10.1351/PAC-CON-10-10-25
- “Graphene Oxide-Assisted Dispersion of Pristine Multiwalled Carbon Nanotubes in Aqueous Media”- Liu T. et al, Journal of Physical Chemistry C¸ 2010, DOI: 10.1021/jp103745g
This information has been sourced, reviewed and adapted from materials provided by Cheap Tubes Inc.
For more information on this source, please visit Cheap Tubes Inc.