Shampoo bar too soft/crumbly

Hello all !
I have been trying lately to make a nice solid shampoo bar, base on sodium coco sulfate surfactant that I get in solid form (small balls shape).
I have not been able to find the right texture but the cleansing effect is realy good and I am happy with that.
The problem is that it is rather soft (softer than a usual cold processed soap bar for instance), and that it sticks to the surface in the shower when you store it. Meaning when you pick it up the next time, you will lose some of the bar material that will remain on the storage surface.

Here is my formula, I would like to know if anything strikes out to you to get some ideas for improving it. Thanks a lot for your help !

sodium coco sulfate    56.1%
oat kernel powder (50 microns)    10.0%
coco glucoside (ca 50%)    7.0%
Emulsence (cationic emulsifier)    5.0%
Brassica alcohol    4.0%
Cocoa butter    3.5%
Rice bran wax    3.0%
citric acid (solid)    2.8%
Hydrolyzed rice protein (liquid ca. 30%)    2.0%
essential oils    2.2%
coconut oil    1.0%
carrot CO2 extract    1.0%
Vitamin E (ca 70%)    1.0%
Hydrolyzed wheat protein (solid/powder)    1.0%
D-panthenol (ca. 75%)    0.5%


  • lmoscalmosca Member
    You have got an incredibly large amount of fatty matter in your shampoo bar. 
    13+% (including the brassica alcohol). (softness, melting)

    You also have got a very heavy hygroscopic (water absorbing) load, 15+% (panthenol, oats, hydrolyzed proteins, citric acid). (stickiness)

    How do you manufacture your bars? Do you mix and compress everything together? Do you go through melt phase? (crumbly texture)

    Other question, how do you correct your pH? SCS and Coco-glucoside have very high pH which is destructive for hair and scalp. Adding solid citric acid will not change that. 

    Also, as a quick note, you do not have a preservative for something that regularly comes in contact with water (and, with all the bug food you have in there, will absorb a lot of it). Definitely unsafe.

  • Hello Imosca,

    Thanks for your constructive feedback, here are my comments points per points:

    - large amount of fatty matter:
    I thought this would be the main part that would hold the bar together. I added more fats that are solid at room temperature rather than liquid ones. Like cocoa butter and brassica alcohol which has a melting point of 57°C.
    I also add these fats so it can be nurrishing for the hair and scalp to try soften the harshness of surfactant.
    I tried to add rice bran wax also to help hardenning the bar, it does help a bit. But just a bit :)

    - hygroscopic load:
    I did not know the oat and hydrolized proteins where hygroscopic, thanks for the feedback. The 10% oat powder I did not put before and I tried here thinking it would help with compacting. Since the mainsurfactant has rather large ball shape, I thought I would add this as a small size "filler".

    - manufacturing process:
    To be honest this part is not yet figured out, but for now I keep the main surfactant (SCS) and oat powder in a bowl.
    Separately, I melt the oil phase with the cationic emulsifier, to which I add then the water phase (which include the citric acid in solution). I then pour this hot liquid into the bowl with surfactant and mix to get to and homogenous dough.
    I then add the essential oils and put in a mold.
    I have a manual press, but for now that is not satisfactory at all, I cannot remove easily the bar from the mold as it is too sticky, even though I put non stick paper on the mold parts (you know the one for cooking).

    Alternatively, I tried also to heat the oil part along with the main solid surfactant, but I did not see any difference, plus I only heat to 85°C max and SCS would not melt anyway at this temperature...

    - pH correction
    that is the purpose of the citric I add here, and like I said I dilute it in the water phase (coco glucoside + hydrolized rice protein + panthenol), making sure that I do not go over 55% concentration in the 'actual' water content of that phase.
    To check the pH, I dilute the final bar @10% in distilled water and measure. I did not do it on this one specificaly, but on similar recipe the dilution was showing pH of around 5.5 which I was happy with.

    - Preservation
    I have not yet made lab tests on it, but I would like ideally to make a self preserving bar.
    I am thinking of testing the water activity, hoping that it is below 0.7, and possibly do challenge test to see if even after going under the shower it can resists.

    I hope I was clear, please do no hesitate to tell me if it was not :)
    I really appreciate your help! I am looking forward to reading your comments.
  • AgateAgate Member
    How long did you let it dry before use?
  • Hi Agate,

    I would say I mostly tried a day or two after making. I have some older sample but they do not seem to get much better (harder) with time.
  • lmoscalmosca Member
    The main problem that I see is that you've put yourself in a catch-22 situation.
    It's a multivariate type of problem.

    You have opted for very strong surfactants (SCS and CG), those are typically very cleansing. To compensate for the stripping of oils from your hair and scalp, you resort to adding hard fats. Now, those also have the effect on the surfactant, by pre-maturely trapping some of it (and vice versa) and reducing its ability to clean the hair (concomitantly, they reduce foam). You can see that you cannot change one without changing the other.

    The second issue that you have is the homogeneity of your mixture.
    There you have beads of SCS. You cannot melt them (too high of a melting temp). There is no way out of this, as you cannot dissolve it in the oil phase, and you have a too little of a water phase (otherwise loaded with other stuff) to dissolve a large amount of it. At this point you have an non-homogeneous mixture that needs a binder. That is why most opt for butters low melt oils and fatty alcohols.

    What you have here is a continuous matrix made of hard waxes, oils, intespersed by insoluble powders (SCS beads, then all your hydrolyzed proteins, water soluble ingredients). Upon contact with water, water will migrate towards the regions of your bar that contain the most hydrophilic ingredients (humectants, proteins, surfactants) and will dissolve them at different rates.

    Now, some of those surfactant will dissolve whatever lipophilic compound they see. In an homogeneous case scenario your oil phase would be completely homogeneous, but it's not. You poured melted fats over a large amount of room temperature solids. The fats slowly cool down as you mix them with the powders. What happened here is that you obtained a fractional crystallization of the higher melting point components (mainly the stearic fraction of cocoa butter). Whatever is left behind solidifies amorphously and will be the first one to be dissolved by the surfactants. 
    This will create preferential channels where water will accumulate during use and continuing dissolving your bar from the inside out. That's why you are obtaining a crumbly texture (I suppose it gets worse during use? if not, there might be another reason).

    I personally do not agree with your choice of fatty matter. Cocoa butter is comedogenic and clogs pores. You don't want that on your face, and you want that even less on your scalp, as it may increase the rate of hair loss, it is also draggy, and this increases the forces to which your hair are subjected to when brushing/combing/drying. If you stick with fatty alcohols, they have lower comedogenicity and they improve lubricity of the scalp/hair.

    I also noticed that you have Carrot extract and vitamin E oil both at 1%. 
    If you are adding them for claim, then reduce them to 0.1%  (or less, even).
    If you are adding them not for claim, there is no scientific evidence that they do anything to hair.
    If you are using vit E as anti-oxidant, then at 1% it will have the opposite effect, potentially promoting rancidity (by shuttling electrons and protons back and forth). Reduce below 0.5, or even better 0.25%

    Regarding you pH, you are unfortunately limited by the fact that the SCS is not homogeneous to the mixture. I am glad to see that your final mixture after neutralization is 5.5.
    Which method did you use to determine this amount?
    What I do is: I take away a certain amount of mixture and record its weight (W1), dissolve it water to a 10% final concentration, to that add solution of citric acid (V1) (or NaOH if I need to go the other way, but it rarely happens for shampoos and syndets bars), until I reach the pH I want. Then, I calculate residual batch size (what remains after the sample, W2) and from there calculate how much solution of citric acid to add to the mixture (W2/W1)*V1. 
    You can do that on the initial surfactants+water soluble ingredients without oil phase (oils will never change pH, unless they are really bad).
    Proteins and aminoacids usually act as buffers of pH, but depending on manufacturers, you may have slightly more alkaline or acidic batches.

    Your stickiness problems is dual, on one side you have wet, sticky stuff (oats, proteins, panthenol). On the other you have fatty materials that have not completely solidified (maybe). 
    You can help unmolding by freezing the mold. However, as you remove the bar from the mold, it will start condensing water (if you live in humid climate, even more so).

    As @Agate said, you will have to wait until most water has evaporated from your bar (this may take anywhere from 24 hours to a few days).

    Undoubtedly, you solid bar will have a very low water activity. However, there is no way you can monitor said water activity during the use of the shampoo bar. And since a shampoo bar touches not only water, but dirty hair, hands, surfaces, and is exposed to air all of the time, you have an explosive cocktail of microbial contamination and food. Remember that mold grows even when there is no apparent food (think about the grout on your bathroom tiles), just because they get wet every day. Better safe than sorry, add a preservative!

    In my opinion you will have a better chance at reformulating this bar from scratch. 

    - Change surfactants, and change their forms (powders vs beads or noodles), If you want to keep SCS, you can increase mildness by using Cocamidopropyl betaine (CAPB), instead of Coco-glucoside (it's one of the worse surfactants in terms of sensorials, if you ask me). Or go for blends containing AOS, SCI, SLSA.

    - By increasing mildness, you won't need all that fatty cargo, and by not using coarse materials, you won't need a binder, as the amount of water during your manufacturing will be enough to cement everything together. If you want to keep some as a binder, switch butters and waxes for fatty alcohols and cationic emulsifiers as substantive conditioners. 

    - If you want to keep oils/butters, reduce them to a claim ingredient (0.5% or less, even 0.01%), they are only detrimental to a shampoo. If you opt for liquid oils, steer clear from those that have high comedogenic ratings and with high levels of oleic acid (Malassezia loves oleic acid). Opt for liquid waxes instead, or polyunsaturated oils with high linoleic / linolenic fractions (but those are more prone to become rancid).

    - Decrease the complexity of your formula, you have two hydrolyzed proteins and panthenol there, use only one. They are film formers, but this is also a rinse off, so not much of them will stay. Plus, you have a protein/polysaccharide powder (oat), that adds to the water retention ability of the shampoo bar.

    - Use a preservative!
  • BelassiBelassi Member
    ^^ Fantastically good analysis. ^^
    Cosmetic Brand Creation. Concept to name to IMPI search to logo and brand registration. In-house graphic design inc. Pantone specs. Cosmetic label and box design & graphics.
  • deneuxbendeneuxben Member
    edited April 8

    I feel very honored that you are taking some of your time to answer to me in great depth. I really appreciate a lot. I am very detailed oriented and very keen on understanding the science that is at play here to help me further master the formula and process. So your answers look just amazing to me :)

    Here are my comments:

    Surfactant choice:

    My aim is to have a blend of surfactant that are accepted by organic certification body. If I am not wrong, SCS along with sodium lauryl sulfate are the only solid ones that are accepted. But I do not have access to sodium lauryl sulfate right now that is why I stick with SCS. Plus, I do not know if blending sodium lauryl sulfate with SCS would be beneficial.

    Secondary surfactant: I was under the impression that Coco glucoside was on the softer side amongst surfactants. Would lauryl glucoside be softer? (Aren’t long chain surfactants softer than the short chained ones ?). I could also have access to sodium cocoyl glutanate or Disodium/Sodium Cocoyl Glutamate, but I do not know how this one compare to the others?

    Preferential channel/fat solidification: I understand what you are saying here, but I am not 100% sure this is what is happening. I think I have both type of samples, some got crumbly, but some feels like they get harder with use. So I am curious, what may be the other reason, you seemed to have something in mind ?

    But if this is what’s happening, and given the fact that I probably cannot change the process in a way that does a quick cooling to have homogenous fats in an amorphous state. What can I do better here? Reduce or remove the virgin oils/butter in favor of the fatty alcohol?

     Choice of fatty matter: I thought cocoa butter will help in hardening my bar and aso be good for the hair, isn’t stearic acid supposed to be a bit conditionning?

    I understand fatty alcohol would be more effective that way. But I would like to incorporate virgin oils/butter in my product. Noted for the comedogenicity, I thought it was not critical for hair and scalp.

     Carrot extract: this is to color the product. I found that any colored vegetal powder, like some ayurvedic plants, or even clay, tend to not be stable and the product turns to an ugly brown after use. I found that coloring the oil fraction with that extract is more stable.

     Vitamine E: I have heard a lot that vitamine E can be pro-oxydizing if added in too large quantity, but I am a bit shooting in the dark here, trying anything between 0.25 to 1% max usually. I thought up to 1% was still safe. I will reduce the amount then. Just to make sure, the percentage you proposed are based on my 70% ca concentration or you talk in term of active matter ?

     pH adjustment:

    To determine the amount, it has just been trial and errors, I have not done it the way you do. But I have well understood it I think and I will test this protocol. I guess I should aim for a 4 – 5.5

     Stickiness: I understand your point for unmolding, I’ll try that. But the other problem is that the bar would stick to the surface you depose it on (in your shower), and when you next pick it up, some material gets ripped off. Would reducing the amount of hygroscopic material would help reduce this problem?


    I get your point, but if I try to be critic here, wouldn’t the preservative preserve only the “inside” of the product, and here the main exposure is the water that will surround the bar. So would that be any effective against this risk here? Note that I would be using naturally derived preservative which may be a little less effective maybe than some synthetic ones.

     Reformulating from scratch: I agree with you, I have been doing little changes for some time on this already complex formula without much success. I need a fresh start.

    I do not think I understand fully the following: “and by not using coarse materials, you won't need a binder, as the amount of water during your manufacturing will be enough to cement everything together”

    What is the coarse material you are refering to? my surfactants?

     Also, can you help me understand how the water present in the process, which will then eventually evaporate (will all of it evaporates given enough time ? my guess would be NO since we have hygroscopic material and the surfactant which is mainly hydrophilic) helps in binding the whole thing together ? I mean I heard that already once, but I do not understand the science that is at play here. I think this would help me understand better what I need to change in my formula: more water phase ? more oil phase ? so far that is not clear to me, I was just trying to avoid too much water in it, relative to my concern for preservation.

     Reduce complexity of the formula: Got it, I will keep only one of these ingredients.

     Preservative: I will start researching what type of preservative would be compatible for that type of product and risk exposure.

  • AgateAgate Member
    I've not yet made a shampoo bar myself, I have just read in multiple places that many shampoo bars benefit from extended drying time. One example:
    Something I’ve learned in my solid shampoo experiments is the benefit of extended drying periods. Much like soap, the shampoo bar lasts longer if it dries longer. While a day or two is fine, I find at least a week is great. I’ve made some particularly soft bars that seemed like they were destined to be shower slop, but after 6 weeks of aging they turned into brilliant hard bars that are surviving just fine in the shower.

    I'm not confident that this alone will resolve your problem, but did want to point it out in case the fix is just that simple.

    I don't have much else to say about all of the above, only that Disodium/Sodium Cocoyl Glutamate is a very popular choice in the German natural cosmetics market, giving a better hair feel than Coco glucoside, though I don't know how these properties change when interacting with SCS.

  • Hello Agate,
    Thanks for pointing that out, the drying time. It will surely help. At least, it cannot hurt :smile: 

    and thanks for the feedback on the sodium cocoyl glutamate since I never used it, im glad to hear from you that it is giving good hair feel and better than coco glucoside. I will buy some next time I purchase ingredient ;)

  • lmoscalmosca Member
    @deneuxben absolutely, I am glad you were not overwhelmed by it :wink:

    I am not the best person to ask about Organic certifications et similia. Perhaps someone else can chime in regarding surfactants. It will likely depend on your geographic area and which kind of standard you want to adhere to. 
    USDA regulates the label "Organic" in the US for what concern agricultural products. So there are no true organic surfactants, you can use "organic ingredients" or "raw materials" but every surfactant needs some kind of physical and chemical process to produce, and the "Organic" label will disappear. You can adhere to the use of organic ingredients (as in agriculturally derived) and organic manufacturing / traceability, according to the NOP (national organic program) and have your product certified.

    COSMOS allows for surfactants like the ones you and @Agate mentioned. In addition, you will find lauroamphoacetate is also ECOcert compliant. I don't think AOS, SCI, and SLSA are COSMOS compliant (SLSa is ECOcert).

    In terms of coco-glucoside, among the series of glucosides, is perhaps the harsher. Decyl glucosides is usually regarded as the mildest of all. If you have access to that it gives more consistent results and it's going to be "toning down" the SCS (or SLS if you have it).
    Blending SCS and SLS will not change much (if the final % ASM stays the same). 
    As a side note, most SLS is an "enriched" mixture of lauryl sulfate. See a thread from Agate a couple of days ago.

    As secondary surfactants, my favorite is, hands down, CAPB. It is COSMOS-Okayed. Very mild, and support foaming of the primary surfactants.

    It's interesting that you are observing both some samples going crumbly, and some going hard. I still think that the homogeneity of your mixture is a problem here. As for why some your bars go hard, then I will try to explain it as a cementing effect. Water goes in, dissolves some of your water solubles, redistributes through the bar, and when it evaporates, it deposits them back.

    Stearic acid is not available as free fatty acid in cocoa butter, but as a triglyceride. At low percentages, stearic acid helps lubricity of the hair, however, I find it draggy above 1-2%.

    Comedogenicity is as important for the hair. Clogging the scalp, or allowing detritus and sebum accumulation in the scalp are common factors in hair loss. 
    The health of the hair follicle is of paramount importance in all cases of alopecia. If your follicles are dying out or are damaged then your hair start thinning out.
    Fatty alcohols and "lighter" oils with low oleic fractions are preferred (because of Malassezia proliferation, you want to go light on oils, this commensal ubiquitous fungus thrives on oils and spits out free fatty acids from its metabolism, the one that has been found most irritating for the skin is oleic acid).

    It's interesting that carrot extract gives you a stable coloration. How long have you had the samples colored with carrot extract maintain their coloring for? Whenever I tried to use natural colorants they inevitably go brown or gray after a couple of months at best. Now I just embrace whatever color (mostly white or off white), or use synthetics dyes or pigments if I want a color.

    For vit E, just reduce it below 0.5 or even 0.1%. It really does not do much to hair and the more you put, the more you risk rancidity and off-smells. Ultimately, you could just leave it out if you don't have many unsaturations.

    For the stickiness problem, one way to go would be reducing hygroscopics. Also, just do not put it on a flat surface. You will always have some material getting dissolved and gluing back your bar to the surface. Use a soap dish with tall ridges or bumps, so that all the water drains and air circulates all around the bar. A dry shampoo bar should not feel tacky. It must feel like touching chalk or have a smooth surface with a waxy appearance (if you use high contents of butters and oils).

    In terms of homogeneity and coarseness, it looks like you have pellets of SCS. Those will not dissolve fast enough during your formulation phase to disperse the surfactant in the mixture. Having coarse / non uniform particle sizes is a common problem in compounding solids. The more uniform the particle sizes are, the better the mixing and homogeneity of the final product. Here you have a heterogeneous amphiphilic part (SCS) which is bound together with a mixture of hydrophilic and hydrophobic matrices (other surfactants and water solubles, and fats, respectively), that usually do not like each other, won't completely mix, and will likely form separate domains (or phases) upon solidifying. Wherever you have two solid phases touching each other, you have a "fault" it is called a continuous boundary defect in chemistry. That's where your material is more likely to break apart, hence the crumbly texture.
    If you reduce the size of particles you maximize homogeneity and reduce the possibility of it being crumbly.

    For water content, you will never be able to completely remove it. There will be always a residual content of water. This is what is called the hydration water. Imagine things like salt, sugars, alcohols, and charged compounds (cationic, anionic, amphoterics) all come with a few molecules of water that are bound to the polar group with some sort of weakish bond (electrostatic, hydrogen bonds). Unless you heat, and apply vacuum for a long period of time you will never remove them. What you can remove is the "solvation" water, the water that was there as a solvent. There is a lot of chemistry beyond that, but in general the content of "solvated" water in a material will depend on its vapor pressure and the vapor pressure of water in the air surrounding your material (which can be approximated by relative humidity). 
    Overall, most of the water loss happens during the first few days. You can check that by weighing a sample bar on a scale every 12 hours. Eventually, you will see the weight stabilizing around a certain value (it will still go down, but less so). You can do a couple of tests on your samples to see an optimal "drying time" and compare it other properties, like hardness, foaming ability etc...
    Now the good news, the hydration water, the one that doesn't go away just by air drying, is not important for you. It won't promote microbial growth, because it's tightly bound and cannot be utilized effectively by microbes.

    That's why solid products can virtually be unpreserved, for theoretical purposes, as their water activity is so low that nothing can grow on them - while from the practical point of view a preservative is needed when there is even the possibility of an accidental contact with water, and even more so with those products that for sure will be in contact with water. That water in excess will permeate into the bar and will be your growth solvent for microbes.
    The preservative will be dispersed all within you mixture, if you choose one that has both lipophilic and hydrophilic growth inhibitors. You need that so both the lipophilic and hydrophilic parts of your bar are protected, and at the same time it is not just "leached" away by water. 

    Please keep us posted on updates of your formulas!

  • deneuxbendeneuxben Member
    edited April 10

    Hello @Imosca,

    I read your comment on Agate’s thread and it was interesting to read that SCS would be more energy efficient than SLS since you do not have to purify the lauric fraction.

     I have the same experience as you for natural colorant, I found them not stable. So far carrot extract seems to be stable, I use it in other products as well, but also I cannot say I run proper stability test, it is more of personal observation over few weeks, sometimes months. Sometimes I put some sample at 40/50°C also. But then I am stuck with orange ! Well, I have hope I can play with the green from tamanu oil, I love that shade of green. Maybe play one day with blue hue of chamazulene.


    SCS is found only in beads right ? or can I find it as a smaller size or powder ? The current one I have is about 1mm in diameter.

    I understand your point regarding the heterogeneity in terms of polar affinity. To make it better, since the main surfactant is high HLB, I should probably favor a larger water phase rather than a large oil phase isn’t it ? I will test this theory by making two simple formulas (6 ingredients): one with high oil phase, one with larger water phase


    Very interesting your comment on hydration water. I was not familiar with the concept, but I totally get it now.

     So today: doing two batches to test the knew knowledge you taught me ;)

    I’ll post again if you are interested by the results. Thanks a ton again !

  • PerryPerry Administrator, Professional Chemist
    @deneuxben - FYI on colorants.  It is illegal (at least in the US) to use colorants in cosmetics that are not approved by the FDA. Plant derived colorants that are not listed on the FDA approved colorant list cannot be use.

  • Thank you @Perry, but I am in Europe, and not planning to play with synthetic colorant. I'll try my best with the natural ones :smile:
  • PerryPerry Administrator, Professional Chemist
    Ah.  Well, here is the EU regulations on colorants. They also have a list you are supposed to follow.

  • lmoscalmosca Member
    @Perry this is an interesting issue (approved colorants).

    Carrot SCO2 extract, depending on source or raw material (peels or flesh) and conditions of extraction (pressure, flow and eventual co-solvent), can have a different content of beta-carotene (usually other carotenes and other xanthophyllins). In some cases, it can be up of the majority of the extract. 

    According to FDA regs, both beta carotene and carrot oil can be used for food coloring, but only beta carotene only is allowed for cosmetics. In case of beta-carotene it should pass certain tests (or titers, purity and minimum of 96% spectrophotometric assay). That means that not all of the SCO2 carrot extracts might qualify, but some may.
    Another reason to always check / ask for a certificate of analysis.

  • deneuxbendeneuxben Member
    edited April 10

    In my case the raw material are the roots, it is what is called a total extract (I think it relate to the process pressure, here I think total is for high pressure)

    Here is what the supplier documents says:

    0,15 -0,21 % total carotenes calculated as beta-carotene corresponding to 2500 - 3500 i.U. provitamin A, alpha, beta-, gamma-, delta-, epsilon-carotene in natural isomerical distribution, lycopine, traces of essential and fatty oil, lipophilic flavones, jojoba oil.

  • AgateAgate Member
    edited April 11
    @Perry Do the same regulations apply for colour(ed) materials which have another purpose in the formula, either functional or as a claims ingredient? Could one argue that carrot oil is a claims ingredient or has some sort of benefit for the formula, but just happens to turn the product orange in the process?
  • PerryPerry Administrator, Professional Chemist
    @Agate - I can't confidently speak about EU regulations.  But for the FDA, it's written in the regulations that you can't do this. Technically claims ingredients are not allowed either but that gets ignored. 

    This is however, a legal question not a scientific one. If you do this, you better have a good lawyer as you would face significant fines if the FDA decides they want to go after you.

  • AgateAgate Member
    @Perry Thanks for the warning, I definitely don't want to set myself up for trouble with the FDA.
  • deneuxbendeneuxben Member
    edited April 13
    Hello @Imosca,
    One question I meant to ask. I learnt that we normally do not mix anionic surfactant with cationic ones. But here it seems to be fine. Do you confirm it is ok in this type of formula to mix all sorts of surfactant ? In my case I will have anionic (SCS), non ionic (coco glucoside) and cationic (Emulsense: Brassicyl Isoleucinate Esylate).
    My guess is that since they are not part of a solution, it should be fine. But since there is some water content in the formula (like 4-7%), so I guess some get part of a solution and hence precipitate (so they become inactive) ?
    Thank you, have a great day !
  • lmoscalmosca Member
    @deneuxben, while it is widely accepted that you should never mix cationic/anionic surfactants, that's a generalization based on factual evidence. 

    Indeed, there are cases where cationic and anionic mixtures can interact and precipitate from a solution, thereby removing themselves from the product or seriously reducing their "detergency". 

    Not unlike you would use CAPB or decylglucoside to reduce the "harshess" of SDS. What you aim at achieving here is forming a mixed surfactant system that has a synergistic effect, thanks to the presence of a mixture of anionic/cationic/amphoteric/non-ionic surfactants.

    There is evidence that the largest synergy is achieved by mixing anionic/cationic. This is because the structures formed in solution are more tightly packed and can emulsify more "dirt" per number of micelles formed.

    Unfortunately, those are also the mixtures that most likely form precipitates.

    So it's a matter of a delicate balance between the types of surfactants used and their relative ratio, in order to impede or slow down the formation of insoluble materials.

    In your case, you have a solid mixture containing non-ionic, anionic, cationic. These work well together because the non-ionic surfactant helps stabilize the mixture of the other two. Furthermore, the solid state of these limits the ability of these surfactant to form the structures that cause precipitation. 

    One, very basic experiment that I am thinking might help as a way to determine whether a combination of surfactants is suitable would be to prepare solutions of the selected surfactants in DI water at concentrations equal to 1x, 10x, 25x, 50x, 100x (the first or the last two might be difficult to achieve with some surfactants) the CMC of the surfactant and mix them together in the ratio that you would expect to be using them in your final product. Stir for a little bit without making the product foam and let stand. You can observe your mixtures over hours or days to see if they change. Some mixture might flocculate, some may produce powdery precipitate at the bottom (or top of the liquid), some may not change much. In this way, you could build yourself a rough "phase diagram" for mixture of surfactants.
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