Reflection coefficient nonselectivity

These equations correspond, respectively, to the set of Eq. (10.87) for the case of dilute solutions. The value of reflection coefficient cr must depend on the nature of both the solute and the membrane. For the case of volume flow in the absence of the concentration gradient in the permeant solute (AIIS = 0), we see that the quantity (1 - cr) is a direct measure of the extent of coupling between the solute flow and the volume flow. If the membrane is completely nonselective, then a = 0 if the membrane is perfectly selective, permeable only to the solvent, then cr = 1. In most cases, a will lie between 0 and 1. 

A reflection coefficient characterizes some particular solute interacting with a specific membrane. In addition, oy depends on the solvent on either side of the membrane — water is the only solvent that we will consider. Two extreme conditions can describe the passage of solutes impermeability, which leads to the maximum value of 1 for the reflection coefficient, and nonselectivity, where ay is 0. A reflection coefficient of zero may describe the movement of a solute across a very coarse barrier (one with large pores) that cannot distinguish or select between solute and solvent molecules also, it may refer to the passage through a membrane of a molecule very similar in size and structure to water. Impermeability describes the limiting case in which water can cross some membrane but the solute cannot. 

---