Charged Colloids Electrical Charge Distribution at Interfaces

1 Charged Colloids (Electrical Charge Distribution at Interfaces) 

It is obvious that the concentration of positive ions will decrease as one approaches the surface of the positively charged surface (charge-charge repulsion). On the other 

This shows that positive ions are repelled, while negative ions are attracted to the positively charged surface. At a reasonably far distance from the particle, n+ = ir (as required by the electroneutrality). Through some simple assumptions, one can obtain an expression for / (r), as a function of distance, r, from the surface as 

As expected, the D-H theory tells us that ions tend to cluster around the central ion. A fundamental property of the counterion distribution is the thickness of the ion atmosphere. This thickness is determined by the quantity Debye length or Debye radius (1/k). The magnitude of 1/k has dimension in centimeters, as follows  

FIGURE 7.6 Variation (decrease) in electrostatic potential with distance of separation as a function of electrolyte concentration (ionic strength). 

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