The effects of the shqpe and size of soil particle and fiber, as well as the effects of zeta potentials en the interaetion between a seil particle and fiber were theoretically investigated. An equation for potential energy of the interaction between dissimilar electrical double iayers was derived on the basis of a sphere/cylinder model. Equations of the interaction for three different models, i.e., sphere/cylinder, sphere/infinite flat plate and sphere/sphere were compared. As far as practical sizes of a soil particle and fiber in detergent solution is concerned, the difference of the potential energy among three models is very small (Table 1). The difference in the zeta potentials between a soil particle and fiber (Ci, Cs) has a large influence en the maximum value of the total potential energy (iVT, .). Despite a constant CieCz value, VT, . decreases rapidly with the increase of C2/Ci ratio (Figs. 2, 3). The effect of C2/Ci ratio on VT, max was expressed by an exponential function (Fig. 3), and the stability parameter for heterocoagulation, OH, was defined as
OH= 2, exp(-1 ( 1-1, )), 1
The relation between eH ancl VT, ... is linear (Fig. 4) and the value of OH corresponds to the amount of deposited Fe203 onto fabrics (Fig. 5).