On the nanoscale, particles flow in unexpected ways

Oct 25, 2011

Researchers studying how fluids travel through nanoscale channels were surprised to discover that the fluids don't flow equally well in all directions. Contrary to the behavior in the macroscale world, the researchers discovered that methyl alcohol, when it was placed in a network of nanoscale channels in a mineral known as a zeolite, diffused 1,000 times faster in one direction than another. This is the first known evidence of such highly unequal diffusion of molecules in a nanoporous material. This highly lopsided flow occurred despite the fact that the diameters of the respective channels are quite similar. In the mineral, two types of nanoscale channels are present: 8-ring and 10-ring channels. The numbers refers to the relative size of the pores in the material, though they are extremely close in size with only subtle differences in geometry. The methyl alcohol molecules were stored initially inside an optical cell.

At the beginning of the experiment, the pressure in the surrounding atmosphere is increased instantaneously and kept constant for the rest of the experiment. The molecules then enter the zeolite voluntarily since they naturally prefer to be in the zeolite than in the . Once inside the mineral, the researchers measured the particle concentration at various points along the pores. From these profiles, they were able to calculate the particle flux (number of particles that cross a certain area in a certain time) and observed the highly biased flow.

Earlier research reported that the diffusivity of a guest molecule inside a pore network is extremely sensitive to the ratio of the pore window and molecule diameter, particularly if both quantities are close to each other, as was the case with the channels and the methyl alcohol atoms. The researchers in this study speculate that since the 8-ring window is slightly smaller than the 10-ring window, a smaller diffusivity (and therefore a smaller flux) might be expected. Another reason might be the different (straight in the case of the 10-ring channels versus windows and cavities in the 8-ring channels).

Presented in the AIP's Journal of Chemical Physics, this apparently counterintuitive discovery has far-reaching implications for the understanding, development, and exploitation of novel microscopic materials, including nanotubes and "intelligent" cell membranes for purposeful drug delivery, the functionality of which is based on an extreme direction dependence of molecular mobilities.

Explore further: Tiny wires could provide a big energy boost

More information: "Micro-imaging of transient guest profiles in nano-channels" by F. Hibbe et al. is accepted for publication in the Journal of Chemical Physics.

Related Stories

Blueprint from the interior of a catalyst

Sep 22, 2009

Irregularities in industrial catalysts can inhibit the conversion of crude oil, Utrecht University chemists have concluded. They were the first to provide a detailed blueprint of the interior of a commercially used catalyst ...

New zeolite is discovered

Oct 18, 2006

A Spanish-led team of geologists has reported discovering a porous material with a new, highly open framework structure.

Revolution in understanding of ion channel regulation

Jan 30, 2008

A study at Rush University Medical Center in Chicago published this week in the online version of Biophysical Journal proposes that bubbles may control the opening and closing of ion channels. This new understanding of the ...

Recommended for you

Tiny wires could provide a big energy boost

1 hour ago

Wearable electronic devices for health and fitness monitoring are a rapidly growing area of consumer electronics; one of their biggest limitations is the capacity of their tiny batteries to deliver enough ...

Graphene sheets enable ultrasound transmitters

1 hour ago

University of California, Berkeley, physicists have used graphene to build lightweight ultrasonic loudspeakers and microphones, enabling people to mimic bats or dolphins' ability to use sound to communicate ...

Project uses crowd computing to improve water filtration

19 hours ago

Nearly 800 million people worldwide don't have access to safe drinking water, and some 2.5 billion people live in precariously unsanitary conditions, according to the Centers for Disease Control and Prevention. ...

Engineering the world's smallest nanocrystal

23 hours ago

In the natural world, proteins use the process of biomineralization to incorporate metallic elements into tissues, using it to create diverse materials such as seashells, teeth, and bones. However, the way ...

A stretchy mesh heater for sore muscles

Jul 03, 2015

If you suffer from chronic muscle pain a doctor will likely recommend for you to apply heat to the injury. But how do you effectively wrap that heat around a joint? Korean Scientists at the Center for Nanoparticle ...

Polymer mold makes perfect silicon nanostructures

Jul 03, 2015

Using molds to shape things is as old as humanity. In the Bronze Age, the copper-tin alloy was melted and cast into weapons in ceramic molds. Today, injection and extrusion molding shape hot liquids into ...

User comments : 3

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Oct 25, 2011
I cannot find which direction is the preferred direction. I would expect that to be the first thing revealed in an article with the very first sentence "Researchers studying how fluids travel through nanoscale channels were surprised to discover that the fluids don't flow equally well in all directions."

The title states "On the nanoscale, particles flow in unexpected ways" but I would like to get a clue as to what happened that was unexpected.

I am guessing that "direction" has nothing to do with what happened at all. And equally I am suspicious that the "unexpected" may have something to do with the channel diameters. To say the results of the experiment are unexpected and we have the 10 micron and 8 micron channels I just have to work out what was expected to have a guess as to what really happened. Unfortunately, I have no expectations therefore I would like to know which channel received the most flow.
not rated yet Oct 25, 2011
The smaller channel has greater capillary assistance but the larger channel would have less channel wall resistance so which one was expected and why? and which one got the flow?

Assuming that "direction" was a red herring and that the same results happened no matter the orientation.
not rated yet Oct 26, 2011
" fluids don't flow equally well in all directions " ..how could they in a material that doesn't have a geometry that exhibits equidistantly spaced walls ?

I'm not too up on FD, but Darcy's law..?

" the discharge rate of fluid will often be different through different formation materials (or even through the same material, in a different direction) even if the same pressure gradient exists in both cases. "


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.