Experimental BLM systems

Typical BLM currents are of the order of 10-100 pA for applied dc voltages of about 20 mV. Given that the membrane covers an area of approximately 0.0075 cm and is of the order of 5nm thick, the following data are typical  

The technique described above results in bilayers containing trapped solvent which supposedly leads to poor reproducibility in electrochemical measurements. Accordingly, a number of designs have been generated in recent years to produce solvent-free bilayers. However, if measurement trends are all that is required the above will suffice. 

When the membrane is completely thinned and stable, various stimulants can be introduced into the electrolyte in one compartment with stirring, and the conductance can be monitored over a suitable period of time. One interesting variation of this experiment was the incorporation of a special flow-through cell to allow the system to be included in a flow injection apparatus (20). In this way, the conductance can be measured as plugs of stimulant flow past a bilayer membrane surface. 

In view of the difficulties usually experienced in producing BLM of area 0.008 cm, porous structures have been used to form mini-membranes. Two examples of this are nylon polymer films grown at an interface and polycarbonate films normally employed in organic chemistry for the purpose of filtration (21,22). In the former case, a nylon film was synthesized at the interface between water and an organic solvent. Electron microscopy showed that the polymer structure was close-packed on one with a Swiss-cheese structure on the other. Treatment of the films with lipid solution resulted in functional mini-membranes. Polycarbonate films can be employed in a similar manner. Although such systems are relatively simple to work with, one large imponderable is the overall area of membrane produced for study. 

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