Carbon nanotubes speed up fluids

Researchers from the University of Kentucky have shown that carbon nanotube (CNT) membranes "permit a fluid flow nearly 10,000 to 100,000 times faster than conventional fluid flow theory would predict because of the nanotubes' nearly friction-free surface." These membranes could soon be used for drug patches.

According to a University of Kentucky news release, researchers have shown that carbon nanotube (CNT) membranes with pores measuring 7 nanometers in diameter "permit a fluid flow nearly 10,000 to 100,000 times faster than conventional fluid flow theory would predict because of the nanotubes' nearly friction-free surface." As the fabrication process of these CNT membranes can easily scale to large areas, this new discovery could allow for "sophisticated chemical separations, trans-dermal drug delivery and selective chemical sensing."

But why are fluids going so fast? Here is a short explanation.

Membranes composed of manmade carbon nanotubes permit a fluid flow nearly 10,000 to 100,000 times faster than conventional fluid flow theory would predict because of the nanotubes' nearly friction-free surface.

Below is an illustration of a carbon nanotube membrane (Credit: University of Kentucky).

A carbon nanotube membrane

This research work has been published as a brief communication by Nature under the title "Enhanced flow in carbon nanotubes" (Vol. 438, Issue 44, November 3, 2005). Here is a link to this full paper. Below are two short quotes taken from the conclusions.

We conclude that these high fluid velocities are possible because of a frictionless surface at the carbon-nanotube wall. This result could be explained in conventional terms of slip lengths, which are remarkably long.
The membrane fabrication is scalable to large areas [...] and each side of the membrane can be independently modified with different functional groups. These advantages also make the aligned carbon-nanotube membrane a promising mimic of protein channels for transdermal drug delivery and selective chemical sensing.

Nature adds that the University of Kentucky has filed a US utility patent application concerning the fabrication of carbon nanotube membranes. This patent has been filed by Dr. Bruce Hinds who worked on these membranes with his research group.

This document from the University of Kentucky tells us more about these "Aligned Nanotubule Membranes" and how they can be used for carrying drugs, like in drug patches.

A drug patch is a thin sheet of material, or membrane, that is coated on one surface with a pharmaceutical. When the uncoated surface is affixed to a person's skin, the pharmaceutical passes through the membrane to contact and enter the person's skin. Ideally, the membrane would allow only the pharmaceutical to pass through the patch, but not other substances, so that the pharmaceutical would not be contaminated by substances like skin perspiration.
The inventors have devised a process for producing membranes that allow some molecules to pass from one side of the membrane to the other, while blocking the transit of other molecules. The membranes may be chemically treated to further limit which molecules can pass.

Several years will pass before before the patent can be approved and applied to real patches.

Sources: University of Kentucky news release, via EurekAlert!, November 3, 2005; and various web sites

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