Date of Award


Degree Type


Degree Name

Departmental Honors


Plants, Soils, and Climate


Sharma and de Lima (1992) have proposed a model based on Fixman's theoretical development of charged macromolecules in external fields (1980). There are three types of charges considered: the fixed surface charges that are covalently bonded, the layer of bound counterions, and the diffuse layer (Fixman, 1980, Lyklema, 1983 ). Figure (1) shows these different layers. Other common theories, such as Schurr's only consider the bound counterions and the diffuse layer. Schurr assumes that the diffuse layer ions can exchange with the electrolyte. A consequence of this assumption is the lack of polarization of the diffuse layer. This leads to an over estimation of the conductivity and permittivity of clay suspensions (Lima 1992). Fixman's model allows polarization of the diffuse layer, shown in figure (2). Fixman's model is different from other models because it accounts for the motion of the ions tangentially and radially in the diffuse layer around a macromolecule. Other models neglect this tangential motion (Lima, 1992)



Faculty Mentor

Dani Cir

Departmental Honors Advisor

Rouph W. MacAden