Permeation of electroactive solutes through ultrathin polymeric films on electrode surfaces

this and the molecular size discrimination rule out transport through larger-than-moleculardimensional channels and pinholes in the film. The film permeability process is described as membrane diffusion. Relatively pinhole-free films are preparable as thin as 20 - 40 A.The rates of permeation of a series of electroactive solutes, bromide, ferrocene, benzoquinone, diquat, (Ru(bpy)2C12), [Fe(bpy)2 (CN) 2], and [Ru(bpy)2(py)Cl] have been measured through ultrathin, electrochemically polynerized films like poly-[Ru(vbpy)3 . The films are coated on Pt disk electrodes. The permeabilities, expressed as PDs pol , the product of a partition coefficient and a diffusion coefficient in the film, range from very fast (bromide, > 4 x 10" cm2 /sec.) to measurable and sensitive to solute size and charge (2 - 58 x 10" cm2/sec.) to immeasurably slow ([Ru(bpy)2(py)Cl] +, < 7 x 10 1 cm2/sec.). The permeation rates vary linearly with film thicknes