While investigating the flow of fluids via nanoscale channels, scientists unexpectedly found that the flow of the fluids is not the same in all directions, which is contrary to the macroscale world.
The discovery, reported in the Journal of Chemical Physics of the American Institute of Physics, is beneficial as it is possible to study, develop and use innovative microscopic materials such as intelligent cell membranes and nanotubes for drug delivery applications.
During the study, methanol is made to flow through a series of nanoscale channels in a nanoporous material called zeolite. The scientists discovered that the flow of methanol was 1,000 folds quicker in one direction when compared to the other. This highly asymmetrical flow happened even when the diameter of the nano-channels is equal.
The methanol molecules were stockpiled firstly within an optical cell. The nanoporous mineral consists of 8-ring and 10-ring nanoscale channels of which the numbers represent the comparative size of the pores in the mineral. The two kinds of channels are almost similar in size with only slight variations in their geometry.
During the start of the study, the surrounding atmospheric pressure is instantaneously increased and then maintained at a constant value throughout the experiment. Since methanol has the tendency to stay in the zeolite instead of the gas phase, the methanol molecules voluntarily enter the mineral. Once within the zeolite, the scientists measured the concentration of the particles at different points across the pores. They used these values to measure the particle flux and studied the highly lopsided flow.
Previous study revealed that a guest molecule’s diffusivity within a pore network varies with the ratio between the pore window and the diameter of the molecule, especially if both the amounts are almost the same. This was the case with the study between the methanol molecules and the zeolite channels. Since the 10-ring window is slightly bigger than the 8-ring window, the scientists believe that the diffusivity of the particle inside the 8-ring window is lower than that of the 10-ring window. The difference in the pore geometry of the respective nano-channels is also another reason, according to the researchers. The 8-ring channels had cavities and windows, while the 10-ring channels were straight.
Source: http://www.aip.org