Stearic Acid by Polarized Light Microscopy


Stearic acid is a saturated fatty acid which contains an 18 carbon chain. It has the IUPAC name octadecanoid acid and a chemical formula of C17H35CO2H. Stearic acid is typically obtained from fats and/or oils by a processed called saponification, which is conducted using hot water usually above 200 Degrees C. Typically fats and oils which are rich in Stearic acid are far more common in animal fat than vegetable fats.

Typically Stearic acid is used because of its bifunctional character, it has a polar head group which can attach to metal cations, whilst also having a nonpolar chain that allows for solubility in organic solvents. This combination see’s the compound used as surfactant’s and softening agents.


How it was done:

Since the melting point of Stearic acid is fairly low (<70 Degrees C), it can easily be melted by a Bunsen burner. In order to achieve this the slide was progressively passed through the flame being careful not to either burn the Stearic acid, or break the slide. Once the acid had melted it was left to cool and re-solidify.

The image was then captured using my normal polarized microscopy setup, which included;

Because the depth of field is relatively small, some images did require focus stacking which is where Helicon Remote & Focus came into the picture (pardon the pun).


Images: (Click to enlarge)

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