::::THIS SECTION DESCRIBES SOME ESSENTIAL PRINCIPLES AND AS WELL AS SOME IMPORTANT EVERYDAY EXAMPLES

::::WHERE SURFACE CHEMISTRY APPLICATIONS ARE RELEVANT::::::::

I.....Distance Between Molecules:::

ALL MOLECULAR INTERACTIONS ARE
DEPENDENT ON THE DISTANCE BETWEEN MOLECULES--------

Example:::WATER ( at room temperature and pressure )

Volume of 1 mole water::::

Liquid = 18 cc

Gas = 22.4 Liters

Ratio of Volume of Gas:Liquid = ca. 1000

Ratio of distance in Gas:Liquid = (1000)exp 1/3 = 10

Actually, one may compare the states of solid - liquid - gas to how the people are arrnged in any football arena, as follows::

...SOLID state...People sitting in chairs.

...LIQUID state...People moving out of the arena.

...GAS state...Football players running around

II....SURFACE TENSION OF A LIQUID

The subject of physical chemistry concerns with properties which are needed to describe any system. Therefore one needs to describe the molecules in the system as accurately as possible. It is thus of interest to understand the situation about the near neighbour molecules in any system.

Molecules in the bulk water (for example) are surrounded by twice as many neighbor molecules than a molecule at the surface. The ratio of near neighbor molecules (surface:bulk phase) is thus half for these two states. Surface tension thus acts to compensate for this difference.

III....Adsorption of Surface-active substances (soaps; detergents)

Ethanol is soluble in water. The surface tension of water (72 nM/m (dynes/cm)) reduces slowly to about 30 mN/m when ethanol is added to water. However, when soap or detergent is added to water the surface tension also decreases to about 30 mN/m. One needs about 50% ethanol to achieve the same effect as 1 g/liter for a typical detergent,

About 100 years ago the dry cell battery was invented. It consisted of zinc + mercury (30%) and other chemicals. The role of mercury was to control the passive zinc system when the battery was not under use. The modern dry cell battery is now based on using detergents (about 50 ppm) instead of mercury. This shows that surface chemistry has an important application in battery technology.

V....OIL SPILL & CLEANUP

Oil spill is a very important example of surface chemistry application process.

Oil and water do not mix. However, by reducing the interfacial tension (IFT) at oil - water interface, one can achieve emulsions. The IFT of oil - water is ca. 50 mN/m. By adding surface active agents (SAA) one can reduce IFT to less than 1 mN/m. On abrupt shaking the oil drops break-up into very minute size thus producing an emulsion. Such emulsions are created, for instance, in the clean-up of oil spills ( as in the Mexico Gulf ).

However, when the reservoir is at a high pressure ( every 1 km depth gives rise to ca. 100 atm pressure), then one must make investigations under high pressures in order to treat such oil spills. High pressure instruments are available in labs which can guide the techs to use the correct treatment procedure. For instance, hexadecane becomes solid around 30 atm pressure.

Furthermore, since the composition of oil differs from place to place, the chemicals needed for such process will be different. Thus the role of surface chemistry is a vital application area in this field of pollution problem.