Kulim KHT Critical Micelle Concentration UMT

 Critical Micelle Concentration Experiments

 Theory of Critical Micelle Concentration Experiments

 Definition

Certain molecules can be classified according to their affinity towards polar and non-polar solutes. An affinity towards polar substances such as water is said to be hydrophilic, conversely an affinity towards non-polar substances such as hydrocarbons is said to be hydrophobic. A molecule may be either completely hydrophobic or hydrophilic, or it could have portions that are hydrophilic and portions that are hydrophobic. Such a molecule is said to be amphiphilic.

Amphiphilic molecules are very interesting, especially in the way they interact with water. The behavior can be considered to be similar to that of a magnet- the two ends of the molecule have opposite polarity and the water has the same polarity as one of the ends. The end with the same polarity as water is repelled away from the water (hydrophobic) and the end with the opposite polarity is attracted towards the water (hydrophilic). Two optional configurations exist, surfactants and micelles.  

This type of arrangement occurs at the boundary between any polar or non-polar liquid and air, if a non-polar liquid is used then the hydrophobic portion points downwards and the hydrophilic portion points upwards. The presence of these molecules at the surface disrupts the cohesive energy of the surface and thus lowers the surface tension. Such molecules are called surfactants, short for surface active molecules.

The other possible arrangement is with a cluster of molecules forming a ball within the liquid, known as a micelle. In the case of a polar liquid such as water the hydrophilic portions make up the exterior of the ball and the hydrophobic portions make up the interior.

In a non-polar liquid the arrangement would be such that the hydrophilic portions are pointed towards the center of the molecule and the hydrophobic portions are pointed away from the center. The formation of micelles is less favored than surfactants, which allows the investigation of amphiphiles through comparing surface tension with the concentration