Electrostatic Theory Coulombs Law

The above five mechanisms for the formation of surface charges cover the great majority of examples encountered in colloidal system. In order to appreciate the significance of their formation and activity in the context of colloidal systems, it is necessary to return to some basic principles of electrostatics. 

The fundamental law governing interactions between charged species was introduced in the preceding chapter. As a reminder, however, for the interaction of two charges qi and Q2 in a vacuum (Fei) separated by a distance r, the law takes the form 

For charges of the same sign, w r) will be positive and the interaction will be repulsive if of opposite charge, it will be attractive. 

Consider for a moment that a charge is isolated in space. It will produce an electric field at a point r, such that the work necessary to bring a unit electrical charge from infinity to distance r from qi will be equal to qi/(4iTeoer). That quantity of work is defined as the electrical potential at r due to the 

When applied to the situation involving charged particles and Coulomb s law, Equation (5.3) predicts that if there exists a negative electrical potential ip at some point in an electrolyte solution, then in the region of that point the concentration of positive charges, c+, will be given by 

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