PRESSURE-DRIVEN FLOW EXPERIMENTS IN MOLECULARLY NARROW, STRAIGHT PORES OF MOLECULAR DIMENSION IN MICA

Hexane, dodecane, hexadecane, and OMCTS to (octamethylcyclotetrasiloxane) were forced to flow through track-etched mica membranes in a series of pressure drop-flow rate experiments. The sizes of membrane pores ranged from semiaxis sizes of about 30 Angstrom to about 300 Angstrom. The track-etched pores in a particular mica membrane are practically identical in cross section and in length, and their number can be accurately estimated, permitting the flow through a membrane to be predicted and compared to measurements. If the alkanes and OMCTS had strongly physisorbed to the pore walls, this physisorption would have been expected to lower the flow rate expected for a given pressure drop and bulk fluid viscosity. No such results of strong physisorption were observed, even in the smallest mica pores, where they would be expected to manifest themselves if present. These results are contrasted with results from the surface-force apparatus, where strong physisorption effects have been reported for fluids confined in molecularly narrow regions between sheets of mica.