Copley-Scott Blair phenomenon and electric double layer

Abstract

The apparent viscosity of blood measured with a capillary viscometer is influenced not only by the size of the capillary tube (sigma effect), but also by its wall surface condition. Copley, Scott Blair et al. reported that the apparent viscosities always showed a decrease when blood, plasma or serum were in contact with fibrin as compared with glass and other surfaces such as silicone (Copley-Scott Blair phenomenon). In order to offer a reasonable explanation of the Copley-Scott Blair phenomenon, the role of the electric double layer existing at the interface between the fibrin-coated glass surface and blood, plasma or serum has been emphasized. The influence of an electric double layer upon the Poiseuille flow of an electrolyte solution has been treated theoretically. The effect of an electric double layer is expressed through a nondimensional parameter $\mathit{\alpha }=\mathit{\epsilon }\mathit{\sigma }\mathit{\zeta }\mathrm{/}\mathrm{(}2\mathit{\pi }\mathrm{K}\mathit{\eta }\mathrm{R}\mathrm{)}$ where σ and ζ are respectively the surface charge density and zeta potential of the electric double layer, ε, K and η are respectively the dielectric constant, specific conductivity and viscosity of the Newtonian liquid, and R is the radius of the tube. The parameter α becomes significant when the product $\mathit{\sigma }\mathit{\zeta }$ is large, as is expected for fibrin surfaces, while it will take small values for glass, silicone and polyethylene surfaces. Moreover, the parameter α becomes significant for small values of R, showing that the effect of an electric double layer becomes especially significant in capillaries and microvessels. Experimental confirmation of our theory and the extension of our theory to blood are desirable.