In reality if we know the activity non-ionic surfactant have on the skin, they are more skin-friendly . On the other hand anionic surfactants are more accepted from the consumers because of their foaming activity, considered the mayor mean of their effectiveness as cleansing agent,also if this is not true. Cationic surfactant have an antiseptic power but are more irritative for the eye  mucous membranes. In my opinion the best way to formulate  a cleansing agent is to balance the non-ionic with anionic surfactants mixture.

Thanks morganti for the comment. I still wonder why anionics have better foaming ability than cationic and non ionic. Do u have any comments on that? Thanks 😊 

Probably it is all about their HLB and water loving ability. 

An interesting question which opens up more questions - foam is very much dependent on the conditions in which you make your measurement. Cationic, nonionic and anionics surfactants all produce a lot of foam at low concentration in pure clean water. However the level of foam is much reduce by antifoam in real systems where dirt and water hardness are present. The amount of foam will then depend on how the surfactant responds to the antifoaming agent.

To make comparisons between surfactants you will need to be very specific about the conditions in which you make your measurements.

Tariq: if I am not wrong hlb is irrelevant to anionic surfactants.?? 

James: Good point that u make. However  I am comparing them in DI water. So I guess factors that u mentioned play only minor roles. 

an important point is that the foaming is not necessarily a reason for being good cleaner! actually cationic surfactants are much more activated than the others. but the reason for using non-ionics is that they are more skin- and environment-friendly. if you use any industrial cleaner, they foam less, and clean more. because they are cationic!!! Cationics are even more active than anionics and non-ionics that they can adsorb on the surface in presence of these two, desorbing them. this is what we have in some shampoos. anionics makes the hair dry and mat. adding some cationic surfactant in recipe helps to wash out the remainings of anionics on hair. this is also the same for clothings (softeners). The simple reason for us to use non-ionics is ECONOMY!!!  they are available in nature and they are cheaper than cationics.

Hassas: thanks for detailed comment. I also accept that foaming doesn't reflect cleansing. However I am curious to know why anionics are better than non ionics in terms of foaming. Please advice. Thanks 

Hi can you be more specific about the surfactants you are using. APGs for example are high foaming nonionics which can match anionic actives. 

Are you studying height and stability or dynamic foaming? Stability is dependent on surface activity, stability of the surfactant layer at the interface and the speed at which surfactant can be transported to the interface. The last factor will depend on the size of the micelle aggregates which are present. Cationic actives can form large worm like agregates with poor transport properties. 

I hope this help. 

Dear James - You mentioned that stability of foam depends on surface activity, interface stability and micelle mobility. Can these explain why anionics are better in terms of foaming and cleansing? Can you share some articles/books for that ? Thanks :) 

The stability of the foam depends on avoiding the colapse of the bubbles, and it's possible because the surfactant adsorbs in the air-water interface and can promotes electrostatic repulsion or steric hindrance between two interfaces. In this context, it's possible to make some general considerations:

- Anionic surfactants are better foamers than nonionics, the presence of charge promotes the electrostatical repulsion;

- Nonionics can be foam stabilizer if have a great polar portion to act in the steric effetc (the case of APGs and Poloxamers);

- Cationic have performance worse than anionic due to the higher apolar portion that difficult their packing (they are mostly derived from tertiary amines);

- The cationic surfactants are not that bad in cleansing, they are used in hard surface cleaners/all-purpose cleaners in combinations with alcohol etoxylates.

Sodium alkyl sulfate

Sodium dodecyl sulfate

Sodium dodecylbenzenesulfonate

Sodium laurate

Sodium laureth sulfate

Sodium lauroyl sarcosinate

Sodium myreth sulfate

Sodium nonanoyloxybenzenesulfonate

Sodium pareth sulfate

Sodium stearate

Sulfolipid

 can use any of them Sodium alkyl sulfate

Sodium dodecyl sulfate

Sodium dodecylbenzenesulfonate

Sodium laurate

Sodium laureth sulfate

Sodium lauroyl sarcosinate

Sodium myreth sulfate

Sodium nonanoyloxybenzenesulfonate

Sodium pareth sulfate

Sodium stearate

Sulfolipid

They have different properties and have to be selected depending on the purposes for which we think to use them. The majority may be used as cleansing hair agents with different purposes and different kind of hair,while ,for example, sodium stearate is an emulsifiers agent that give more consistente to an emulsion also .

Foaming is a complex dynamic process. At the heart of it is the need to prevent the thin films of liquid from breaking. If looking at long lived foams the static surface forces between the liquid/air interfaces are important. If the interaction forces are repulsive this will inhibit the film from thinning and improve the foam stability. For anionic surfactants (eg SDS) the adsorption of the surfactant leads to a surface charge and surface potential. This results in an electrostatic repulsion between the surfaces - which will promote stability by maintaining the thickness of the liquid films - thicker films are less likely to break in response to a mechanical disturbance. However, the range of this interaction is dependent on the ionic strength of the solution (characterised by the Debye length). So when the salt concentration gets above mM concentrations the range of the repulsion can become insufficient to stabilise the liquid film - so ionics might not work well in the presence of high salt concentrations such as waste water or sea water. Of course non-ionic surfactants also adsorb to the air-water interface -but they do not provide a charge/potential/electrostatic repulsion. However if the hydrophilic group is bulky it can lead to a steric/hydration repulsion that stabilises foams. Think of this as a repulsion due either to they physical size of the head groups or due to the energy required to dehydrate them. Non-ionis are largely unaffected by electrolyte so they may be better foaming agents when salty water is used.

Note dynamic effects are always important. So the particular effects of each surfactant on the viscoelasticity of the surface are important. These effects are also strongly concentration dependent. So the situation is complex and it is difficult to predict the foaming properties of a surfactant based only on its structure

To some extent, the amount of foaming is enhancing the cleansing for he detergent. Furthermore, the anionic character of it making it more powerful for better detergency actions.