Determination of the quality of surfactants

 

SURFACTANTS:
Anionic Surfacants:
Acidic methylene blue test
Methylene blue is a cationic dye soluble in water and insoluble in chloroform. It can form a blue compound with anionic surfactants which is soluble in chloroform.
Acidic methylene blue solution.
Slowly add 12 g H2SO4 to 50 ml water; after cooling down, add 0.03 g methylene blue and 50 g Na2SO4 anhydrate; dilute the whole solution to 1 l.
Test
Add 5 ml of 1% sample surfactant solution into a mixture of 10 ml methylene blue solution and 5 ml chloroform in a test tube; shake vigorously then allow it to stand until two layers are formed. If the chloroform layer (bottom layer) shows blue, add another 2–3 ml of the surfactant solution. Shake well and leave for layers to form. The chloroform shows as dark blue and the water layer is almost colourless. This is a positive result of the existence of anionic surfactant in the sample solution. This test is suitable for alkylsulphate and alkylbenzolsulphonate surfactants. Soap cannot be tested because it would precipitate in the strong acidic medium.
Basic methylene blue test
Add 1 drop of 5% sample solution to a mixture of 5 ml 0.1% methylene blue solution, 1 ml 1 N NaOH solution and 5 ml chloroform. Shake well and observe the colour of the chloroform layer. If a blue-purple colour is shown, there is an anonic surfactant in the sample. This test is suitable for any type of anionic surfactant.
Thymol blue test
Thymol blue solution is prepared by adding 3 drops of 0.1% thymol blue in every 5 ml of 0.005 N HCl solution. For the test, add 5 ml neutralised sample solution to 5 ml thymol blue solution. Shake well and observe the colour of the mixture. A reddish-purple colour is the evidence of existence of anionic surfactants in the sample solution.
Precipitation test:
A few drops of sample solution are added into 5 ml of 5% p-toluidine hydrochloride aqueous solution. If a white precipitate appears, there is anionic surfactant in the sample solution.
Non-ionic surfactants
Methylene blue test
The test is conducted as in Section 4.3.1, acidic methylene blue test. If the aqueous layer is emulsified to a milk-like state, or both layers have the same colour, the existence of non-ionic surfactants can be confirmed.
Cloud point test


The solubility of polyoxyethylene surfactants is dependent on their hydrogen bonding with water. At a high temperature, the hydrogen bonds of the surfactants would be dissociated leading to lower solubility of the surfactant. Therefore, the solution of the surfactant becomes cloudy at the high temperature. Based on this principle, the polyoxyethylene surfactants can be detected.

Amphoteric surfactants
Amphoteric surfactants contain both anions and cations. They should show positive results when tested using either the basic methylene blue test for anionic surfactants or the alternative bromophenol blue test for cationic surfactants.
A saturated bromine aqueous solution can also be used to determine the type of amphoteric surfactant. Add 5 ml of 1% sample solution to 1.5 ml saturated bromine aqueous solution. Observe the colour of the precipitate. Heat the mixture and observe the change in the precipitate. If the precipitate is a yellow to yellow-orange colour and is dissolved to form a yellow solution after heating, the sample is an imidazoline or alanine type of amphoteric surfactant. If the precipitate is a white to yellow colour and insoluble after heating, the sample is the other type ofamphoteric surfactant.
Active matter content:  Procedures are complicated and mostly potentiometric that I do no know…
Solid Content:
Foaming Test: 
Formation of foam during processing especially in jet and soft-flow type of machineries is a big  headache for the dyer. So in these machines people prefer only no-foaming or very low foaming wetting agents only. Compare two wetting agents by making .01% solution, in two  500 ml measuring jars. Shake the jars for about 3 minutes and keep them intact for some time. Compare the height of the foam. Lower the height better the wetting agent.
Wetting Time:
Exactly weighed 1 grams of untreated grey yarn and wind it in to a small ball (make about 4 or 6 balls). Prepare 1 gpl solution of the wetting agent to be tested. Using a stop watch exactly note the full immersion time of 4 balls placed one after the other just on the surface of the solution. Take the average of this timeings.
Capillary Rise Test:
Prepare 1 gpl  solution of the wetting agent to be tested – use distilled water for preparation.  If you want to compare two samples, prepare the test solution in a two 100 ml beakers. 
Prepare two pieces of 1�? x 8�? size strip of a well scoured RFD poplin fabric. Clip the top edge perpendicular to a steal scale or long glass rod. Immerse 1�? depth of the other end of the strip by suitably holding the scale or glass rod in a stand. Note the time when you dip the fabric end. Watch after 5 minutes. Note how much length the fabric strip has got wetted out.  Higher the height of wetting region better is the capillary rise of the wetting agent.
pH of 1% solution in distilled water:
Solid Content: Evaporate 5 grams of the substance in a pre-weighed crucible at 100-1050C. Find the dry weight and calculate the %.
Specific Gravity: 10 ml of accuarately measured solution is weighed in an electronic balance.
Specific Gravity = weight/volume