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

Hexane, dodecane, hexadecane, and OMCTS to (octamethylcyclotetrasiloxa ne) were forced to flow through track-etched mica membranes in a serie s 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 accu rately estimated, permitting the flow through a membrane to be predict ed and compared to measurements. If the alkanes and OMCTS had strongly physisorbed to the pore walls, this physisorption would have been exp ected to lower the flow rate expected for a given pressure drop and bu lk fluid viscosity. No such results of strong physisorption were obser ved, even in the smallest mica pores, where they would be expected to manifest themselves if present. These results are contrasted with resu lts from the surface-force apparatus, where strong physisorption effec ts have been reported for fluids confined in molecularly narrow region s between sheets of mica.