Can someone please elaborate on the concept behind "surface charge density" in regards to ionic bond strength?

Surface Charge Density is the
electrical charge present on the Interface of two or more
materials, organic or inorganic. There are variances of surface charge depending on
whether the materials are solid, fluid, or gaseous. For example, if you mix oil and
water in a jar, they will not mix and form an interface with a specific surface charge
density; if you mix water and salt, the salt will break down and attach to the water,
forming a different surface charge density.

Ionic
Bond Strength is the measurement of the attraction between oppositely-charged
metallic and non-metallic Ions. One ion loses one or more
electrons, which transfer to the other ion, causing an attraction and an
electrostatic bond between two differently charged ions. Salt
itself is an example of an ionic bond between Sodium and
Chlorine; salt in water is a different ionic bond, this time
between two substances. Also, although Ionic Bonds are technically different from
Covalent Bonds (sharing electrons vs. attractions between
differently charged ions), all ionic bonds are covalent to some
degree.

Briefly, you would use a measurement of Surface
Charge Density to measure the strength of an Ionic Bond, and to figure out if two or
more materials are similar or dissimilar in their individual electrical charges. Any two
materials will have a surface charge at their interface, and substances have charge at
the molecular or atomic level, depending on their covalency.