Synthetic membranes relative permeability

Langmuir-Blodgett films may have value in many applied areas of traditional interest to the industrial chemist, such as adhesion, encapsulation, and catalysis. The permeability characteristics of monolayer assemblies may also find application as synthetic membranes for ultrafine filtration, gas separation, and reverse osmosis. For example, Albrecht et al. (44) proved the eflSciency of polymeric diacetylene monolayers on semipermeable supports in reducing the flow of CH4. One interesting possibility lies in using LB monolayers as lubricants in magnetic tape technology. Unpublished reports have indicated that frictional coeflScients can be reduced markedly when the tape is coated with a few monolayers. In applications such as those listed previously, difiSculties may well be encountered with the mechanical stability of the films. To date, relatively little research has been carried out in this area. 

Figure 1 Relative permeability spectra for synthetic and natural membranes. Curves (1) and (2) represent the glomerular membrane for neutral and anionic solutes, respectively (8), curve (3) hemofiltration membranes (.91, and curve (4) hemodialysis membranes (10), Reproduced with permission from Ref. 52. Copyright 1980 Kidney International.

The membrane must not be attacked by the solvent and must permit the solvent to permeate fast enough to achieve osmotic equilibrium in a reasonable time. If the membrane is too permeable, however, large leakage errors will result. Cellulose and cellulose acetate membranes are (he most widely used types with synthetic polymer solutions. Measurements at the relatively elevated temperatures needed to dissolve semicrystalline polymers are hampered by a general lack of membranes that are durable under these conditions. 

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