There is so much advice available on the internet these days (oh god, I sound like someones grandma) and not all of it is good. In fact, it is safe to say that the vast majority of it is bull crapola really, not because it is wrong, but because it isn’t really likely, possible, practical or applicable. When I’m talking like this I’m focusing on my pet subject, chemistry.
As far as I know chemistry still isn’t drawing in the crowds like other degrees seem to. Law and Medicine remain eternally popular but the humble old chemistry is just a bit too hard, too abstract and too……. full of chemicals I guess. So basically we live in a technically advanced world but one in which very few people know what the hell is going on. Interesting turn of events that.
To illustrate this I had a meeting today about a new cosmetic ingredient that is essentially a feat of chemical genius in spite of it being totally and utterly natural. In fact one could use this ingredient to make nature greater! Playing God or just being smart? I’ll take both and dunk my biscuit in it.
The trouble is that in a world that is almost chemically illiterate ingredient ideas like the above are poorly understood, supported and invested in until they can quite literally spell out their advantage in the kind of plain English that a 5-year-old would grasp which is a shame as there is so much more beauty, enjoyment and satisfaction to be had in life once we understand the detail.
But anyway, this type of situation plays out all over the net every day. In the past year or so I’ve noticed a marked increase in people who come along to the help desk I man overwhelmed and deeply confused after receiving (or reading) so many conflicting reports of what is what on the internet. This is not surprising, I’m sure I’ve blogged about this before but I do want to say it again.
Cosmetic chemistry is an applied chemistry, the devil is in the detail, there is usually more than one answer to a question and not everything that is possible is probable.
I find it relatively easy to discern between the ‘do’s’ and the ‘parrots’ and I think you should be in on this because it saves time:
- The ‘do’s’ will always be happy to say ‘you know what, I don’t really know but I think I know how we might be able to find out’ and no, they don’t mean they will ‘google’ it.
- They understand chemistry AND formulating enough (including how the product is to be manufactured) to be able to break down with you the reasons why certain ingredients will work well together and why others might not.
- They will give you confidence to try to explain what to look out for when (if) things have gone wrong.
- They ask you (and this is VERY important) LOTS of questions about what you are doing BEFORE they jump in with an answer.
- They pre-empt your ‘rookie’ questions and answer them pro-actively to save you the embarrassment.
- They tend not to give blanket ‘just use x’ type answers or use them with a caveat knowing that ‘x’ isn’t the answer for everything.
- They feel happy/ comfortable in sharing how they know what they know, where they went wrong and how they recovered their bad situation.
- They either have evidence to back up their suggestions based on their experimentation or can point you to real third-party science data that will do the same.
- They ask you questions and encourage your input into solving your own problems – teaching by empowerment.
On the other had there are the Parrots.
Parrots generally invest much of their time outside of the lab, listening in to what everyone else is saying before parroting it back louder and stronger so as to sound as knowledgable and authoritarian as possible. Questions you ask are given straight, direct no-if’s, no but’s answers ‘this is what you need’ type of thing and coming back with more questions quickly becomes tedious to them as it means they have to take that question on notice while frantically running around looking for the answer usually without ever setting foot in the lab.
So is what I’m saying nothing more than lab snobbery? ‘Im a chemist’ stuck-up-ed-ness?
No, you don’t need a chemistry degree to do this.
What I’m talking about is lab-reality.
We all know the scenario – we were all going to be perfect drivers that never changed lanes without indicating or daydreamed for a few too many seconds before catching up with the traffic jam BEFORE we got behind the wheel after a long and stressful day’s work…
We were all going to be the perfect pet/ human parent feeding only organic hand-made nourishment to our beloveds BEFORE we got ourselves a family.
We all knew how to make the perfect serum/ shampoo/ moisturiser/ sugar scrub BEFORE we tried to do it for ourselves and make a commercial go of it….
Life, it doesn’t always ‘go’ by the book.
And chemistry is no different.
I enjoy the fact that cosmetic chemistry has been accessible for so many more people and that it is easier than ever (in some respects ) to start-up your own brand – at least here in Australia. But what I do worry about is the growing reality that many people seem to be fumbling around in the dark looking for guidance. Sometimes it’s best to just turn the bloody light on.
Get into the lab as often as you can as there really is no better teacher than real, practical hands-on experience.
I graduated as a chemist a while ago now and have been working professionally in the beauty industry for over 18 years – a time that has, on the one hand gone in the blink of an eye but on the other feels like an eternity.
Anyway, I just wanted to share with you the main thing that keeps me getting up and doing this day after day, week after week, year after year. It is simple, I LOVE it.
The ‘it’ I’m talking about is chemistry, wearable chemistry.
I’m not the kind of girl who raves about a new brand of moisturiser or who wears all the new shades of lipstick or blush but I am the kind of girl who gets very excited about HOW all of this comes into being.
My whole professional world revolves around a joy of chemistry, of understanding what happens when this goes with that, of how it feels, spreads, lasts and ages. I love the detail and never tire of learning more.
Over the last month I’ve been building a new adventure to go along with what I’m doing here. I don’t know how it is going to turn out yet or when it will happen so I’ll leave you hanging on that but what it has done is opened my eyes to the fact that for many science just isn’t fun anymore. Since I started in the beauty industry there has been a feeling that ‘chemical’ is a dirty word and while I’ve never took that sentiment to heart I have to say I got on with it (that mentality) because that’s what was ‘in’. However, I’m becoming increasingly angry at how little interest and understanding exists around chemistry, its beauty and functionality. I make it my mission every day to try to put the fun, beauty and love back into this beautifully elegant science.
So my thinking and mental travelling has taken me back to somewhere around the 1930s when Art Deco was the fashion, an art inspired by brave geometry, new lines, science, the future, inventiveness and bold discoveries. I have gone back to a time when every little boy and girl got a chemistry set for christmas (well, not every one but you know what I mean), when making stuff didn’t involve fear, when great strides were being made in our understanding of the world and our place in it. While there are aspects of the ‘chemical revolution’ that have had less than exciting ramifications it is the energy and ‘can do’ mindset that I’m channeling, the optimism and fun that was to be had.
And on that note I have started to re-organise my office, inspired by the labs of the early part of the 20th century in the hope that I too can channel that enthusiasm and bring the joy back to chemistry.
I know there are lots of different types of emulsifiers but how do different emulsifiers make my emulsion feel?
After all the reading in my last article: The Secret Life Of The Emulsifier I feel it is time to bring things back to the lab again as we try out a very simple yet effective experiment to demonstrate how one might answer that very important question ‘This chemistry is all well and good but how do these emulsifiers FEEL?’
I developed a very simple formula based on a common non-ionic emulsifier – Cetearyl Alcohol and Cetearyl Glucoside. This formula was then replicated with different emulsifiers, one from each different class (except silicone). The products were evaluated by an expert panel of five people as well as having their viscosity checked before being evaluated under the microscope. The idea of this base formula was for it to be stable and easy, I wasn’t too bothered about anything else at that stage.
The formula and feedback is not presented to help sway a decision towards or away from a particular type of emulsifier, merely it is to illustrate a point, that the emulsifier can impact everything from viscosity to feel, efficacy to stability. It also demonstrates the importance of optimizing the whole formula so as to get the most out of the emulsifier of choice. Plus there is always room for pairing up on technologies or trying something new!
So the only difference between these formulations is the emulsifier except for the cationic version which was incompatible with the thickener Acacia and Xanthan gum blend. In the cationic I used a cationic guar at the same level.
Formula 1: Cationic (Brassicyl Isoleucinate Esylate (and) Brassica Glycerides (and) Brassica Alcohol)
Formula 2: Anionic (Potassium Cetyl Phosphate)
Formula 3: Non-Ionic (Cetearyl Alcohol, Cetearyl Glucoside
Formula 4: Mixed Anionic/ NonIonic. (Glyceryl Stearate (and) Cetearyl Alcohol (and) Sodium Stearoyl Lactylate)
Formula 5: Non-Ionic Synthetic (Cetearyl Alcohol, Ceteareth-20)
Formula 6: Polymeric (Acrylates/C10-30 Alkyl Acrylate Crosspolymer)
Formula 7: Liquid Crystal Emulsifier (Cetearyl Olivate, Sorbitan Olivate).
Formula 8: HLB balance (Sorbitan Monooleate, PET-20 Sorbitan Monostearate)
Viscosity @ 3.0 Spindle
Thin, high spreading, slightly tacky to touch at first drying to powdery.
Silky, takes a while to absorb, feels substantive after drying.
Easy to rub in
Very thick and creamy, light after feel
Ultra-light, quick break and high spreading. Tacky on drying.
Rich waxy texture, slow spreading
Very light and spreadable
Base formulation used.
|A. Water Phase||Deionised Water||71.95||143.9||Solvent|
|Acacia and Xanthan Gum||0.4||0.8||Thickener/ Stabiliser|
|B. Oil Phase||Jojoba Oil||8||16||Emollient|
|Shea Butter||8||16||Barrier Protection|
|Emulsifier of choice||3||6||Emulsifier|
|Cetearyl Alcohol||1.25||2.5||Emulsion Stabiliser|
|C. Finishing Touches||Natural Vitamin E||0.5||1||Antioxidant|
|Preservative (Phenoxyethanol, Ethylhexylglycerin)||1||2||Broad Spectrum Preservative|
As expected the polymeric emulsifier produced the largest dispersed phase droplets.
Top: Formula 6: Polymeric (Acrylates/C10-30 Alkyl Acrylate Crosspolymer)
Bottom: Formula 5: Non-Ionic Synthetic (Cetearyl Alcohol, Ceteareth-20)
The Cationic emulsifier Vs Anionic Emulsifier.
4 weeks in 40C oven pass at time of going to press.
There really is a lot to take in when developing complex cosmetic formulations including the ionic strength and polarity of your water phase, your marketing departments wishes, the viscosity and feel you are trying to achieve and the packaging you hope to sell in. That said, today we are lucky enough to have at our finger tips a wide range of different ‘drop-in-and-go’ technology to help us balance creativity with tight deadlines. My only hope is that we remain engaged and inspired by the chemistry that underpins this convenience so we can keep on innovating for centuries to come.
These days, one could be forgiven for thinking that creating an emulsion is child’s play. We have available at our fingertips tens, if not hundreds of self-emulsifying pre-blends that require no fiddly HLB calculations or secondary stabilisers. Well, that’s the theory anyway. You see, when you start making skincare formulations the chances are you will mostly be working on relatively simple oil-in-water concepts with stable, predictable actives and a simple vegetable-oil derived dispersed phases. Indeed, it is even possible to make some pretty exciting anti-ageing, brightening or cleansing formulations without hitting any hurdles all of which add to the general feeling of accomplishment for the freshly graduated chemist. But it doesn’t take long for that initial bravado and ‘beginners luck’ to fade and when it does it pays to have a few tricks up your sleeve.
I want to forget for a moment that we have these self-emulsifying blends and concentrate on working from first principals, not so we can do lots of math and get lost on somewhat superfluous detail but so we can design our creams from the ground up, so that we can make anything and so that it has at least a fighting chance of working out for us!
So let’s start by asking ourselves a few questions, what do you need to consider when selecting an emulsifier?
The way I see it there are four main categories that deserve consideration:
- Marketing/ Product Positioning.
- Physical Character
As Cosmetic Chemistry is an applied science I feel it is appropriate to start with the marketing as this is the main reason for us embarking on this formulation work after all – to sell something.
Emulsifier Free Claim.
Like every other aspect of cosmetic formulating trends in emulsifier selection abound. Right now we have an emerging niche of ‘emulsifier free’ creams designed around the philosophy that the emulsifier, being a surface-active ingredient may be a source of irritation for very sensitive skins and that avoiding the use of an emulsifier may make the product more suitable for this demographic. Now this may or may not work out to be true but nevertheless the concept is of interest as there is some truth in the idea that surface-active ingredients (of which emulsifiers are a part) can contribute to a products irritation potential.
So if you don’t use an emulsifier to hold the oil and water together, what do you use?
Small amounts of oil can be held in suspension with the use of thickeners/ stabilisers such as carbomer and even, to a lesser degree xanthan and sclerotium gums. These aren’t emulsifiers and neither are they forming an emulsion, more of a suspension but, if the oil phase is light enough and dispersed well enough these products can be made stable through stearic hindrance – the oil droplets are caught up, as if in a fishing net! Sometimes bentonite clays can also be used in this way to bring opacity to the formula and to provide an electrical repulsion layer into the structure to help repel agglomeration of the dispersed phase.
Another option in this space is a modified acrylate copolymers such as Acrylates/Beheneth-25 Methacrylate Copolymer. Although this particular polymer is best suited to surfactant formulations it does have a role to play in leave-on skincare as it has the benefit of being tolerant to a relatively high level of salt and other water-phase destabilisers making it a versatile choice for the ‘emulsifier-free’ concept developer. The fact that the polymer can stabilize a reasonably sized oil phase while remaining ‘emulsifier free’ paired with its low use levels add to the cost efficiency of this solution. Another interesting feature of these polymeric ‘emulsifier-free’ ingredients is their ability to be sprayed which opens up new doors for the formulator and marketing department.
But what if you are looking to create something a bit richer and with an oil phase more typical of a traditional moisturizer?
Modified lecithin chemistry has become accepted technology in the ‘no emulsifier’ space, especially because these lecithin fractions often have lipid enhancing properties and can be sold on their ‘skin compatibility’ and moisture binding powers. In addition, the phospholipid structure also lends its self to active delivery given how similar in structure they are to human cell membranes (well at least in terms of their chemical constituents). Lecithin chemistry tends towards forming a liquid crystal network in the continuous phase, which both traps and interacts with the dispersed phase in an ultra-stable and skin-compatible three-dimensional structure. A number of companies are now offering a range of modified lecithins suitable for everything from light hypoallergenic milk formulations through to super-rich balms which should please marketing departments the world over but from a chemists perspective it is hard to see how these ingredients have managed to escape the ‘emulsifier’ tag.
Ingredient Origin and Ethics.
Another important consideration for the general public and formulators alike is ingredient sustainability and/or ethics. There is a steady yet growing interest in ‘palm oil free or sustainable palm’ concepts the achieving of which is surprisingly difficult. That said, making an emulsion without adding any palm derived ingredients used to be easy – just use petroleum derived chemicals – but these days that is just as unacceptable for a growing number of brands. The reality is, our enthusiasm for embracing the natural revolution has increased demand for vegetable based feedstock and those of us who have been in the industry for a while know that means either palm (orang-u-tan habitat) or Rapeseed/ canola (pesticides and bees).
So today while it is still not that easy to create a palm free emulsion it is not impossible especially given that our previous ‘emulsifier free’ examples are predominantly palm free (lecithin phospholipids are frequently made from Rapeseed, Egg, Soybean and/or Sunflower). In fact, it would be fair to say that the hardest thing about making a palm free emulsion today is not over which emulsifier to choose but in which supporting ingredients can be used to increase stability, viscosity (without gumminess) and overall skin feel.
INCI Name – It Has To Look Good On The Label!
Still under the guise of marketing issues, the issue of INCI names also comes up here, while ingredient maufacturers do have to abide by a ‘truth in marketing’ legislation when they apply for their INCI names (they can’t just make them up) the reality that a natural sounding INCI will sell more and have better shelf appeal than a more chemical sounding ingredient. This reality has really hit home and that can be both good and bad. In some cases we have very average ingredients (in terms of performance) becoming popular because they have a nice name while outstanding ingredients (that are still natural in many cases) are overlooked.
Show Me The Money!
Another important factor in the marketing basket is price. Emulsifiers can make quite a dent in the formula budget and when comparing something natural to a stock-standard petroleum based emulsifier you can be looking at anything from three to five times the price which of course has to be justified. In many ways this is the acid test – will customers put their money where their ethical mouths are or do we have to sell them another benefit? Blending different technologies together can be a good way to increase performance while managing price and this philosophy has kept many of the older emulsifiers options such as glyceryl stearate SE alive and selling well.
Performance benefits of different technology will be looked at more in the chemistry section but as we are starting to see from some of the claims relating to emulsifier free formulations, the ingredient that holds the oil and water together is, in many cases expected to do so much more besides. When the Olive derived emulsifier Olivem 1000 first came onto the market there was a great deal of interest in its ability to act as an active delivery system as well as the ingredient that just happened to make an emulsion possible. That benefit contributed to the ‘emulsifier free’ marketing tagline (it isn’t an emulsifier, it is an active delivery system) while also helping the cosmetic chemist deliver oil-soluble actives deep into the skin (theoretically). This important dual functionality contributed to the immediate success of this technology, success that continues today in spite of the ingredients relatively high price point compared with older technology or ingredients like cetearyl alcohol which also form liquid crystal structures for a fraction of the price! In terms of intergrating new emulsifier technology into the laboratory these days the real question isn’t the price but how many benefits one gets for that price? Water resistance, barrier protection, long-wear characteristics, increased dispersion of actives, viscosity boosting and rheological benefits are all possible thanks to a combination of science and nature!
3) Physical Character.
Something that we may overlook when considering price is the emulsifier’s physical form and this is because we often just think of emulsions as hot process items and so the form of the emulsifier is not really a talking point. But it doesn’t have to be that way. Electricity prices are rising in many countries and even those with cheap power aren’t in the habit of wasting it so liquid emulsifiers that can be used in cold-process applications can help the formulator to tick a few boxes from sustainability through to the economic benefits of saving time and money. The range of liquid emulsifiers is steadily growing and is worth a look, especially for markets that demand an ultra-light touch finished product with little to no wax or butter content.
Of course we couldn’t talk about emulsifier selection without talking chemistry. The emulsifier is the heart of the formula and while it may often seem like, today the chemistry has all been done for you, as I mentioned in the beginning, there are some very challenging problems that await the professional cosmetic chemist that only an appreciation of the underlying chemistry will help solve!
Anionic emulsifiers are, in some ways the old-fashioned cousins when it comes to emulsifier technology given that soap and borax type emulsions were where the industry started but that doesn’t mean they don’t deserve a second look.
Soap-based emulsifiers can be extremely useful in cleansing formulations but can also form part of a very elegant high-end anti-ageing formulation just as long as your selection of actives is chosen carefully.
Anionic emulsifiers carry a net negative charge in solution and because of that they, like the cationics are sensitive to electrolytes. Anionics benefit from the presence of a little monovalent salt or acid up to a point (as the increased saltiness/ acidity increases the critical micelle concentration and activity of the water phase) but above that the formula can critically fail in a similar way to that which we see occurring in over-salted surfactant blends. Salt content can creep up on you in an active formula as ingredients such as Aloe, Sodium PCA, Seaweed Extracts, Sodium Hyaluronate and even some herbal actives can push the limits and as such, freeze/ thaw stability is an essential part of early anionic emulsion stability testing.
In terms of skin irritation potential, the old pharmacopeia driven Sodium Lauryl Sulfate and its ‘harsh on skin’ reputation has largely been replaced and when we talk about anionic emulsifiers we are now more often talking of the elegant phosphate esters renown for their skin compatibility or gentler surfactants such as the lactylates or glutamates making it entirely possible to make an anionic emulsion that is skin-kind and gentle.
Cationic technology for skincare arose from the wool industry and then transferred into hair care. As hair and skin are both keratin derived it didn’t take long for the benefits of cationics to be harnessed in moisturiser technology. Cationics function very well in formulations that are desired to stay on the skin for a long time such as sunscreens, long-wear make-up and barrier creams. This is because their positive, cationic charge adheres them strongly to the surface of the skin, resisting wash off and wear. A practical example of where Cationic emulsifiers have proved very helpful is in preventing sand from sticking to a freshly-sun-screened body thanks also to its anti-static capacity. Like anionics, cationics are also sensitive to what is going on in the water phase and cope best with a relatively quiet external phase rather than one loaded with additives.
Due to their natural capacity for skin adhesion cationic emulsifiers can be more likely to irritate than other chemical families but that said, in many cases the formulator can work around this – formulating to an acidic pH is advisable. New generation cationic emulsifiers tend to favour long hydrophobic tail (s) as these have the effect of reducing the charge density of the headgroup and thus minimizing irritation potential. This, of course, has to be balanced by the ingredients capacity to form and hold an emulsion. As with anionic emulsifiers, cationics do benefit from a little monovalent salt as this can boost the CMC and as a consequence of that, the viscosity, but beyond a certain point the salt becomes detrimental to stability.
It is important to note that in using a cationic emulsifier system the formulator does rule out the use of pretty much all grades of carbomer and even anionic thickening agents such as xanthan, unmodified guar and tragacanth.
Non-ionics remain the first choice go-to emulsifiers for the majority of applications due to their flexibility and low potential for chemical interaction. It is often a non-ionic emulsifier blend that is chosen first when creating creams with high activity levels or hard-to-stabilise ingredients such as salicylic acid, AHA’s, Zinc Oxide or high strength vitamin C. It was ingredients such as Seppic’s Montanov 68 that first got us hooked on the self-emulsifying blend of non-ionic and freed us from the trials of calculating HLB in a complex oil-phase world. The key benefit of a non-ionic emulsifier is its robust salt tolerance. In fact, the addition of a little non-ionic is recommended in ionic emulsions as the mixed micelles that will form tend to display a dramatically enhanced salt tolerance over the ionic alone. While the presence of self-emulsifying blends has made things easier it doesn’t for a moment mean we shouldn’t consider what is going on inside of our product.
The HLB system is alive and well in the non-ionic world and gives us a great insight into where the emulsifier will orient its self and whether it is able to bring any other features to the product. That said, it is also important to mention the existence of more than one HLB system so that one can compare like with like. Between 1949-1954Griffin developed a pretty robust yet simple HLB system and that is the standard upon which the Span and Tween pairings from ICI were arranged. The method produced a scale ranging from 0-20 indicating what percentage of the emulsifier was hydrophilic. The number given was the percentage hydrophillicity / 5 (so the maximum number 20 related to a molecule being 100% hydrophilic). This simple system was expanded upon by Davie’s in 1957 who, thought that some weight should be given to the functionality of the chemical groups on the molecule. This makes sense given the variety of structures available to give a hydrophilic character. This method is widely used today and is one of the reasons that ionic emulsifiers can be assigned a HLB value, it is also the reason that HLB numbers in their 30’s are found (the maximum HLB in this system is 40).
In both systems both the emulsifier and the oils to be emulsified have a HLB attached to them – the emulsifiers have a real HLB whereas the oils have a required HLB. It is widely accepted that the best emulsifier pairings are formed when a high HLB emulsifier is combined with an emulsifier with a low HLB rather than just selecting the emulsifier with the exact HLB you want to achieve. This combination effect serves to best fill the interface surrounding the continuous and dispersed phase, leaving less room for gaps and therefore increasing stability.
Liquid Crystal Emulsifiers
Liquid Crystal Emulsifiers work on the principal of forming a lamella network in the cream, which most closely mimics the skin barrier thus facilitating the effective delivery of actives. Lecithin naturally works this way as does Olivem 100 and various other combinations available to purchase today.
Because of their skin-like structure, liquid crystal emulsifiers are often desired because of their beautiful aesthetics. While it is possible to create a range of textures using almost any emulsifier, depending on what goes into the rest of the formula, it would be reasonable to say that the liquid crystal generating emulsifier is the most fool-proof way of creating a beautiful texture without too much additional work.
Polymeric emulsifiers are a really good option for those looking for elegant and quick cold-process solutions. Often sold as liquid polymer suspensions these emulsifiers can create anything from lightweight sprayable milks through to thicker, richer creams depending on what they are paired with. While not for the natural market these can be quite a sustainable option due to their low addition rate, the speed with which they can form an emulsion and their cold-processing capabilities. That said, polymeric emulsifiers won’t work in every situation. Often these emulsifiers are acrylic acid polymers that tend to form complexes with cationic species. In addition, the general salt tolerance of acrylates is low (reflecting the overall intolerance of ionic substances). But one large advantage over ionic and, to a certain point the non-ionic emulsifiers is their ability to form highly stable emulsions with a very low level of polymer with a non-polar or very slightly polar oil phase. This makes them the perfect emulsifier for a silicone-based emulsion, even those containing cyclomethicone.
4.a) The Chemistry of the Water Phase.
I have mentioned a few de-stabilising and stabilizing factors while talking about emulsifier chemistry and marketing considerations but now it is time to really focus on this. An emulsion is a combination of two immiscible phases held together by what to many looks and feels like magic! What is really going on is a physical rearrangement of components, all trying to get themselves into a position that means they are exerting the lowest possible amount of energy – those dispersed phase droplets are lazy! The dispersed and continuous phases are influenced by everything that comes into the formula and some things are more disruptive than others.
Lowering the Surface Tension.
The surface tension between oil and water is so high they don’t mix unless you add a surfactant (emulsifier in this situation). We understand that and have discussed the different types of emulsifier that we could add but do we understand what other ingredients do to the products surface tension?
Preservatives and solvents can dramatically alter the surface tension between the oil and water droplets. As we see with our emulsifier, some reduction in surface tension is required to facilitate the development of an emulsion but in other cases the changes are catastrophic and can result in viscosity and emulsion collapse.
Glycerin, Propylene Glycol and Ethanol are common additives in a cosmetic product and can all impact on surface tension. All of these ingredients decrease the polarity of the water phase and the influence of that decrease changes depending on the quantity of additive present although the relationship between dose and effect is not strictly linear. Reducing water phase polarity loosens the grip the water has on the dispersed phase somewhat by toning down the intramolecular forces that make water behave as it does – Van Der Waals, Dipole-Dipole and hydrogen bonding. While all emulsifiers depend on these forces to some degree to stabilize the product, the Ionic emulsifiers depend on them more strongly and are therefore most likely to be influenced by their presence.
A Flood Of Ions
We often talk about salt and saltiness in formulating but what we are really talking about much of the time is the ionic strength of (often) our continuous phase. While we all accept that swapping Demineralised Water for sea water might cause us formulary issues, we are less likely to accept that the actives we carefully measure into our water phase are doing the same. Be they acids, bases or salts an ion rich water phase can cause havoc for the stability of a product.
Ionic charge in the water phase can help increase intramolecular bonding and can also help in the formation of an electronic double layer around the dispersed phase which increases stability but things can go too far, especially with divalent salts such as zinc and with strong acids and oxidizing agents such as glycolic and peroxide. In general the cosmetic chemist is looking to minimize chemical reactions in their formula and so any addition of ions should be thought of as fuelling the fire of chemical rebellion. Every emulsion has its limits plus adding too many ions into the continuous phase will give the product a sticky/ tacky/ salty feel when applied.
4B) Tricky Oil Phases.
When compared to vegetable oils, silicones demonstrate practically no polarity as well as a very different chemical structure – flexible chains vs bulky triglycerides. Because of these differences silicone fluids such as dimethicone and cyclomethicone tend to mix poorly or not at all with vegetable oils in the same formula. If the formulator wishes to create a silicone rich emulsion, the influence of this low polarity should be considered and steps to reduce the polarity of the continuous phase would increase stability and take some of the pressure off the emulsifier as the surface tension between the two phases would be lessened.
Silicone emulsifiers are available from the major silicone manufacturers should be the first port of call for all those looking to create a silicone-dominant emulsion, especially where the silicone phase will be large or even dominant. That said, with careful consideration it is also possible to create a silicone-rich emulsion with non-silicone emulsifiers if the chemistry of the whole product is considered and accounted for.
|Solvent||Polarity||Solubility Parameter (A difference of <2 indicates mutual structural solubility). Based on the theory of ‘like dissolving like’ Journal SCC 1985.
|Cetyl Alcohol / Stearyl Alcohol||8.94 – 8.90|
|White Mineral Oil||7.09|
Is your emulsion going to be salty, acidic, basic or contain a high proportion of solvents that are less polar than water or does it contain Hydrogen Peroxide? If so the best starting point is a non-ionic.
At this point I think it’s best if we head into the lab and do some experimenting.
Catch up with those experiments by clicking through here.
- The stability of emulsions in the presence of additives. GA[I]1#, B. JOVANOVI]2# and S. JOVANOVI]2# 1Institute for Plant Protection and Environment, Teodora Drajzera 9, YU-11000 Belgrade and 2Faculty of Technology and Metallurgy, Karnegijeva 4, YU-11000 Belgrade, Yugoslavia, 2001. http://www.doiserbia.nb.rs/img/doi/0352-5139/2002/0352-51390201031G.pdf
- Solute and Solvent Structure/ Polarity. The Pharmaceutics and Compounding Laboratory. UNC Eshelman School of Pharmacy: http://pharmlabs.unc.edu/labs/solubility/structure.htm
- Using Solubility Parameters in Cosmetics Formulation. C.D Vaughan, Cosmair Inc, 285 Terminal Ave, Clark, NJ, 07066. Jan 1985 http://journal.scconline.org/pdf/cc1985/cc036n05/p00319-p00333.pdf
- Introducing Pemulen Polymeric Emulsifiers. file:///Users/amandafoxon-hill/Downloads/TDS-114_Introducing_Pemulen_Polymeric_Emulsifiers%20(2).pdf
- Emulsion Formation, Stability and Rheology. Tharwat F Tadros. https://www.wiley-vch.de/books/sample/3527319913_c01.pdf
- Cationic emulsifiers: An emerging trend in skin care. Angela Paez and Anna Howe, Degussa Goldshmidt Chemical Company. http://personal-care.evonik.com/product/personal-care/Documents/cosmetic-toiletries-manufacture-worldwide-cationic-emulsifiers-for-skin-care-applications.pdf
- Macol CSA 20 Polyether. BASF data sheet. http://worldaccount.basf.com/wa/NAFTA~en_US/Catalog/ChemicalsNAFTA/doc4/BASF/PRD/30093528/.pdf?asset_type=pi/pdf&language=EN&urn=urn:documentum:eCommerce_sol_EU:09007bb28006d4c2.pdf
- Emulsions – Part 2. Klaus Tauer. MPI Colloids and Interfaces. Am Muhlenberg, D-14476 Golm, Germany. http://www.mpikg.mpg.de/886743/Emulsions_-2.pdf
- A Quantitative Kinetic Theory of Emulsion Type 1. Physical Chemistry of The Emulsifying Agent. J T Davies, University Lecturer in Chemical Engineering, Cambridge. http://www.firp.ula.ve/archivos/historicos/57_Chap_Davies.pdf
- Intermolecular Forces. Forces. http://chemed.chem.purdue.edu/genchem/topicreview/bp/intermol/intermol.html
These things have GONE OFF like a frog in a sock over the last two years as men all over the world grow and groom their face furniture with a pride and enthusiasm second only to a high school girl on the night of her sweet 16th birthday party!
While I’ve formulated a few of these in my time I’ve never used one as try as I might my beard is just not long and luscious enough to warrant the investment but as there are plenty of people who do meet the facial hair criteria for a beard oil I thought it would be good to delve into the claims that beard oils make in order to answer the question ‘what makes a good beard oil?’
So here we go!
Beard Oil Claims.
These are some of the most popular claims made by beard oil brands about their products. In most cases these claims will have been constructed from ingredient literature or from the brands own small-scale experimenting rather than from any formal laboratory testing but that doesn’t necessarily matter given that no beard oils I have looked at make claims relating to the percentage improvement one will get after using said product. So we have a set of claims that are largely subjective but with a side serving of science thrown in for good measure!
- Soften the beard
- Nourishes the hair
- Moisturise the skin
- Non Greasy
- Smell great
Softening and Nourishing
Softening the beard and nourishing the hair kind of go together so I’ll talk about them together. Beard hair is coarser and thicker than the hair on our heads, that said the coarseness of the hair on our heads varies from person to person too so we need to take a few measurements to get an average before jumping to conclusions. After doing that I’ve taken a microscope slide picture of a beard hair vs a head hair from the same person to illustrate my point:
Left hand side: Head hair, Right hand Side: Beard Hair
In terms of softening the hair beard hair can feel coarser and dryer than the hair on our heads and so ‘softening’ it is highly desirable, not least so it can be ‘tamed’ somewhat. However, when it comes to nourishing the hair I think we need to think about more about what we mean by this. All our hair is dead and so it doesn’t need nourishing as in feeding but it can benefit from the application of ingredients that might smooth the cuticle or lock-in moisture. Leave-on vegetable oils can be a reasonable way to do this but there is always the worry that these oils will just slide off and not grab or penetrate. Cationically functional silicon’s are undoubtedly the best way to get a good long-term ‘nourishment’ but are only suitable in products that aren’t being sold as natural or organic. In terms of validating this claim I think it is safe to say that because of the low-level, low-risk nature of these claims most people would be happy with these claims being based on the feedback of a test panel – qualified anecdotal evidence – rather than relying on a hard set of science based numbers. That said, the word ‘nourishing’ is deeply contentions in the world of cosmetic claims and one would be wise to either drop it entirely or replace it with the more fluffy ‘conditions’ and leave it at that.
Moisturising the skin.
As the hairs come out of the skin it is reasonable to use a product that will benefit the skin – healthy skin= healthy hair! In the case of most (but not all) beard oils the moisturising comes not from adding moisture but from locking moisture in. To do this the beard oil has to form an occlusion barrier on the skin surface to lock-in or slow-down the evaporation of water from the skin’s surface. This is a really good plan for people with dry, flaky skin but for those who suffer break-outs or oiliness it can feel a little oppressive and greasy. The greasiness is somewhat reduced by the use of light weight oil fractions, esters and silicon’s rather than pure vegetable oils but as each persons skin is different there will be no one-size-fits-all. In terms of measuring this claim moisture levels in the skin can be measured via a number of methods so this could be tested. Whether test results are required or not is another matter. Again I feel that moisturising in this context is more subjective than scientific and testimonials and expert panel results might do just as well as long as the results are free of bias.
Non-Greasy and Lightweight.
So we touched on this above and mentioned that silicon’s and fractions of oils often feel less greasy and lighter than whole oils (Triglycerides) but not always. Each vegetable oil comes with its own grease-factor and then there is the other factor to consider with cosmetics subjectivity. What one person thinks is greasy and heavy another will lap straight up. It depends on the skin type, the dose of product used and what else is blended into the product. So we try our best knowing that science is only half of the answer! With regards to silicon’s being ‘lighter’ than vegetable oils, the density of dimethicone is around the 965 Kg/M3 mark or more depending on the length of the polymer whereas olive oil is 930Kg/M3 and caster oil is 956 Kg/M3. So weight wise silicone isn’t light. What is is though is flexible and it is that flexibility paired with its ultra-low surface tension that help it to glide evenly across a surface. So the lightness of silicone has more to do with its ability to spread out and leave a thin-film than it does its weight. As an aside the vegetable oil ester Isopropyl Myristate has a density of only 853Kg/ M3 which technically makes it the lightest option I’ve mentioned!
It stands to reason that if guys were used to getting their aromatic loveliness from after-shave that once they stop shaving they need to satisfy that need elsewhere and what better place than a beard oil. Beard oils can be fragranced with perfumes, essential oils or a combination of the two depending on the end result required. As the phrase ‘smells great’ is subjective there’s not a lot else I can add here except to say that it is wise to ensure the fragrance element of a beard oil isn’t likely to irritate and with a leave-on facial product that includes any potential for a phototoxic reaction (reaction between the fragrance/ essential oil and sunlight). The International Fragrance Association (IFRA) classifies beard oils as category 3 along with eye products so that tells me they need to be formulated for delicate skin. Why? Because skin that is actively producing hairs is more permeable than non-hair producing skin as product can travel down the active hair follicle where it may cause trouble.
So Let’s have a look at an example and see what a beard oil can do!
So I took a few drops of beard oil and warmed it in my hands before spreading it through the beard and massaging it in. This is my husband and as you can see he only has a tiny beard (bless him) but you can also clearly see the curls and wayward nature of the beard in the before treatment. I have to admit to not having taken much notice of this before but not I’ve seen how neat it can look with a bit of product I’m impressed!
The after picture was taken after the roughing up that took place in order for me to get the product into the beard. I didn’t comb it but as you can see just one little application tamed the fuzz somewhat! Very happy with that.
A close-up of beard hair pre-treatment. As you can see the hair shows signs of roughness around the edges and is slightly dull in colour.
A close-up of beard hair cuticle after application. No visible build up and pretty shiny as you can see by the reflection on the image.
So let’s have a look at an example product and see what’s in it!
This time I tested the New Directions beard oil as this article is going on their website as part of their resource package. The ingredients New Directions use are listed below. The whole vegetable oils have been chosen for their quick spreadability and light feeling without greasiness, the vitamin E protects the product from oxidising and the caprylic/capric triglyceride plus Oleyl Oleate help to spread the product evenly through the hair. Lastly the naturally derived copolymer helps to both thicken the oil blend and give it a rich but drying feeling on the hair, again so the oily look is avoided.
New Directions Beard Oil Ingredients:
Caprylic/Capric Triglyceride, Grapeseed Oil, Almond Oil, Jojoba Oil, Sunflower Oil, Oleyl Oleate, Vitamin E, Capryloyl Glycerin/ Sebacic Acid Copolymer, Diheptyl Succinate, Soya Bean Oil.
And what’s the verdict on the skin feel?
Having not used a beard oil before I thought my husband might find it a bit greasy on the skin but he didn’t, instead he felt it was nice and soft (his words) and on feeling his beard again myself I’d tend to agree.
Given the coarse nature of beard hair it makes sense to use a grooming product that can soften and ‘condition’ the hair a little and it looks like this product can do just that. From a scientific perspective I see no reason why beard oils made of any slippy, high spreading non-irritating oil won’t work so the exact combination of ingredients you choose to buy or create would be down to personal taste rather than outright functionality. That said some of the minor claims brands want to make about skin health and benefits (anti-microbial, healing, soothing etc) sometimes do require a specific addition such as those listed below. But outside of that anything goes!
Speciality Oils and their specific claims.
Seabuckthorn Oil – Omega 7 anti-inflammatory.
Macadamia Nut oil – Omega 7 Anti-inflammatory.
Tamanu oil – Anti-microbial
Chamomile Oil – Anti-inflammatory.
Acai Oil – Anti-Ageing benefits due to antioxidants and vitamins in oil.
Borage – High Gamma Linoleic Acid for the treatment of very dry skin.
Wheatgerm Oil – High level of vitamin E.
Cherry Kernel Oil – Some natural UV absorbing powers, not enough for an SPF but a good addition to a skin care regimen.
Rosehip Oil – High vitamin A content.
Googling your illness, learning cosmetic science from an online forum, collaborative learning and other modern phenomenon.
I was listening to a discussion about googling your symptoms on the radio between a doctor and the presenter. Rather than dismiss Googling your symptoms and self-diagnosing something the Doctor in question celebrated it. She made a great point, that the person most invested in their health is the patient, they feel what they feel, live how they live and have a personal insight that will forever elude the Doctor. But then she said the best outcomes she’s experienced are when the patient comes in with a mind that is still very much open to consultation, a mind that is aware of the pitfalls of cognitive bias, a mind that recognises the value of an un-attached appraisal of the situation – especially when that ‘other’ mind has professional qualifications and experience in this field.
Next I heard another radio interview this week with a university lecturer who was discussing how, these days students challenge the lecturers more and take a more collaborative approach to learning. He mentioned that it has become common for students to pitch their ideas and to shape the lectures and even the direction of what is taught and that the lecturer has gone from being the un-touchable expert on a pedestal to being part of the process. He felt this was a very good thing, a progression on the old days when lecturer/ student relationships were often more dictatorial (especially at first Degree level) and I’d have to agree just as long as the students recognised and respected at least on one level the value of the lecturers perspective and experience. Something I’m sure most do given their investment in the course.
Lastly this week I found myself reflecting on the way that online forums and blogs contribute to the ideas exchange in cosmetic science. I see these discussions take place, often cooperatively but sometimes quite prescriptive (the person answering often can’t help but tell the questioner exactly how to solve their particular problem). I’ve been feeling increasingly uncomfortable with the trajectory these discussions seem to take and now, with the above two scenarios providing context I can see more clearly why.
With both the doctor/ patient and the student/lecturer relationship examples advancement in technology and changes in social norms (we no longer tend to just look up to ‘authority’ because we should) have led to more open and consultative dialogue between the two parties. In many ways the communication has become more natural and I can really see the benefits of that. But what we still have in both these scenarios are personal relationships conducted in an organised environment (University or Doctors surgery) with a reasonable understanding of what it has taken for each party to get there (qualifications, dedication, time etc). The communication takes place around a specific idea, project or outcome and the context is given due consideration.
What I see (from my perspective) on cosmetic science forums is a mixture of interactions attracting many voices with different background experience and qualifications in an environment that has required very little effort or investment to join. So, we have a virtual ‘free-for-all’ that attracts a mixed bunch of folks, some of whom just dip their toes in when they have a very specific issue to discuss and participate very little in anything else and others who set up a more permanent resident there answering whatever comes along (or much of it). What worries me about this is the way that these online groups can create the illusion of a participant being an expert just by the nature of their participation – answer lots of questions, gain lots of kudos for answering the questions. The audience shifts so there are always fresh eyes who can look over past comments and see which member dominates the answer so as to deduce who is the most experienced or valuable. But this can be a false reality. How can we be sure that the answers given are based on the answerer personal experience and experimentation? Is the loudest voice the best? What real-time qualifications do the questioners have in relation to your question? How relevant is the answer to your unique situation? Did the answerer seek more context before answering? Is the wider context even necessary? Is there any evidence of ‘expert creep’ happening – I classify this as when someone who has a long history in making one area of cosmetics only starts talking authoritatively on another, completely unrelated issue without first qualifying their level of experience. So many questions…
And after being an internet voice for the last 9 years myself I know all too well how easy it is to become revered or elevated to God like status. I’m always trying to shake off the devotees, not least because much of the time I’ve got no idea where I’m going until I get there!
So am I just a whiney whiner (I charge for my advice, well not always but that is my business model) or do I have a point.
Well I wouldn’t be writing this if I felt I was just whining but I do wish to acknowledge that just like the doctors who initially hated google or the lecturers who felt like throwing the chalk board wiper at the know-it-all students I have had my ‘throw-my-dummy-out-of-the-pram’ moment. BUT I recognise that was just me reacting to the change, for seeing the bad before the good – you know, like many of us do when faced with something they don’t understand. I’ve since seen the light so to speak! Forums are just one of the many ways we communicate now and their lack of rules and framework do contribute to their free-flowing nature. I acknowledge that there is no reason that these forums can’t be good good or even better than what we had before – they are certainly more equitable in many ways. Being able to go onto a forum and ask questions for free would feel good if I was looking for answers on something. Who doesn’t like free stuff!
So what is the down side? Where’s the catch?
Well in my mind it’s one of proximity, contract and validation.
There is a big difference between a mutually invested one-on-one relationship and a group chat – that’s the proximity. One doesn’t have to be in the same room to be close, more one has to be in the same head space – on the same page and not just transactionally, I’m talking solidly invested in it – project wise.
The contract is the framework in which the parties operate. In the lecturer/ student or doctor patient framework there is the security of knowing the backgrounds of each participant, what they are trying to achieve and why. Where the information they are offering is coming from, it’s limits and how it might be tested.
Finally the validation, the chance to test the ideas, collaborate further, confirm what worked and what didn’t and discuss all of that with the sole agenda of coming to a workable conclusion.
Forums are going to continue to be part of our cosmetic science world and I absolutely do see the use of them, especially if participants go in with their eyes open to the possibility that they may, at times get caught up in a case of ‘the blind leading the blind’ and in others be offered lots of well-meaning but not strictly relevant or applicable advice.
So how I’d approach the online forum environment is to see it as a party, you can meet lots of good people, have a few little conversations and enjoy a very good time but the real business of working these new contacts should come later in a more sober environment where the full glory of your problem/ project can be discussed, evaluated and understood. People skim read, jump to conclusions and jump in too quickly in the heat of the moment and that can cost time, money and the sanity of the questioner who can sometimes be left feeling unsure as to whom to trust – a hard call when you really don’t know anyone.
I do hope you guys continue to enjoy your online relationships (including the one you have with my blog) and I also hope that they provide you with the love, support and ideas you need to move your projects onwards and upwards. But I also hope you remember that it is easy to be a keyboard warrior and a whole lot harder to back that up in a commercial laboratory environment and that never looks likely to change. Oh and don’t forget that cosmetic science is ‘applied’ and is often subjective so that is rarely only one answer to a question and that’s what makes it all magic.
Good old, honest, traditional castile soap, loved by hippies and the home-made set the world over for its simplicity and elegance but there is one thing that bothers me about this ingredient and that’s it’s high pH.
Why am I bothered by such a trifling matter?
A couple of reasons:
- I find castile soap overly drying for my eczema prone skin and I feel the very high pH (9-11.5) doesn’t help.
- It stings the eyes.
- Many of my customers want to use castile as an ingredient in an otherwise pH balanced natural product. I’ve had requests from those wanting to use it in a combination face wash to those putting it in cleaning products. To do this I have to be able to adjust the pH.
So is pH Adjustment possible?
Yes and no. Mainly no.
So the pH of castile soap in its natural state is between 9-11.5 which is typical for soap which naturally has a high pH whether it is in a bar form or as a liquid. This is because it relies on Lye (Sodium Hydroxide or Potassium Hydroxide) to rip the oils heads off (that’s how I imagine it) and replace them with ‘soap’ (sodium or potassium salts) while releasing the glycerin from the triglycerides. The resulting saponified fatty acids have naturally high pH levels (usually between 8-11 but most often between 9.5-11) and any residual lye will also contribute to giving the soap bar a high pH (although soap manufacturers usually make sure there is no residual lye).
One of the reports I’ve used to establish the pH of the saponified fats is this one: The Hydrolysis of Soap Solutions. III. Values of pH and the Absence of Fatty Acid as Free Liquid or Solid JAMES W. McBAIN, P. LAURI:NT 1 and LUCILLE M. JOHN, 2 Department of Chemistry, Stanford University, California. It is available to purchase from Springer online.
pH changes with concentration and temperature so these numbers are just to illustrate the point rather than be absolute references but you can quickly see where the high pH of soap comes from.
Potassium Stearate pH 10.05
Sodium Stearate pH of a 5% Aqueous solution is 10.7 (MSDS online)
Potassium Laurate pH 10
Sodium Laurate pH 9.78
Potassium Myristate pH 10.28
Sodium Myristate pH 9.81
Potassium Palmitate pH 9.81
Sodium Palmitate pH 10.1
The above ingredients and their pH’s represent what is formed when you saponify an oil. You are creating new chemicals that have some degree of water solubility and that have relatively high pH values. So, even if ALL of the lye is used up in your soap, your soap will still have a high pH (pH 7 is neutral) because you have created chemicals that have a high pH.
Here is what stearic acid/ Sodium Stearate looks like:
So what happens when you try and adjust the pH down?
There is a precipitation reaction that occurs when you add acid to the castile soap base. This doesn’t happen straight away but it does happen relatively quickly showing us that there is a reaction going on.
Here are the results of an experiment we carried out in the New Directions Laboratory:
So we established that the pH of the New Directions Castile Soap could be reduced from 10.27 to 9.03 using a small amount of citric acid and careful stirring.
Soap and citric acid.
Next we wanted to see if the pH of Castile Soap could be changed by using another method/ acid just in case there was a particular issue with Citric Acid.
We chose to look at diluting the Castile with more Glycerin (as some customers had said that helped to make the soap more mild), with more vegetable oil (based on the theory that any excess lye would soap up the oil and thus lower the pH) or with lactic acid – an alternative to citric.
The results are here. This batch of Castile was a bit lower than the last and measured a starting pH of 9.6.
So with regards to pH adjustment it became clear that none of the above worked but what these results did show, especially with the sunflower oil addition was that it is unlikely the resting pH of the Castile Soap was due to excess lye thus supporting what we know about the pH of the saponified fatty acids.
So what is going on with the Castile Soap when we attempt to adjust the pH downwards?
Well that’s the question.
The typical reaction we talk about it:
Acid + Base = Salt + Water.
But we have an acid and a salt so does that mean we make a salt and water?
Or do we make nothing?
We must be doing something or there wouldn’t be a precipitation happening…..
When using Citric Acid we could rip the sodium from the Sodium Myristate/ Stearate etc and form Sodium Citrate salt but would that really happen? If it did happen would there be a precipitate? The answer is probably not and there would be no precipitate as Sodium Citrate is readily water soluble.
So is there some kind of complex happening? There must be something going on..
There are a few things that might be going on, Let’s look at each one in turn.
Firstly there is a reaction called ‘Protonation’.
So if we remember what our soap is made of (and refer to the hand-drawn picture above) we see the bit of the molecule that makes the soap water soluble has a Na+ (or a K+) part and a COO- bit when it is in water.
When an acid comes along it can donate a proton to the COO- group making it COOH. You can read more about this reaction here.
Converting a soap to an acid is something that can happen but it is unlikely to happen in every situation unless the resulting compounds are less energy intensive to make (thermodynamically attractive). Citric (or lactic) acids are weak acids so they are not exactly powerful enough to do this reaction on their own as the salt is still the favoured format given the (still) high pH and the relative weakness of the acid. However, if this reaction could occur it is true that the salt form of the molecule is more soluble than the acid and in the case of these huge carboxylic acids this head-swap leads to the precipitation of the insoluble fatty acid.
So is it likely that the precipitate is formed by a reaction of glycerin and the citric acid?
Glycerin is a bi-product of saponification and is retained in castile soap to help keep it liquid. It is well known that biopolymers can be manufactured by combining citric acid with glycerin so it is reasonable to question if this is happening here, especially given that the resulting polymer would form a precipitate. However, in order to form a precipitate the polymerisation reaction has to take place at temperatures in excess of 100C and over a prolonged period of time rather than instantaneously at room temperature. So I guess it remains a possibility that something like this is happening but it is unlikely to be what is going on here. Here is some more information on this reaction.
Does the citric acid just reverse (or un-do) the lye reaction?
So we have triglycerides, add lye and get soap.
So why not take soap, add an acid and get triglycerides?
Or even monoglycerides
Or what else….. Fatty acids?
Is there a chance that the citric acid can replace the -O-Na+ with a -OH?
That’s what we discussed in the protonation bit above. It’s not that likely.
OK so what on earth is going on?
Well, my theory centres on something more physical than chemical which is all too often the case with cosmetic chemistry. I think that the addition of acid interferes with the micelle formation and that the cloudiness is caused by the water-hating tail groups being temporarily (or permanently) flipped open or disrupted. Acidity in the water disrupts the status quo of the micelles and if too much acid is added the micelle structure changes completely, the stearates are unable to orientate into micelles which leaves their water insoluble part with no option but to run for the hills – or the top of the beaker in most cases. I think this is happening as the pH is not changing enough to provide the right environment for such a vigorous chemical reaction but I have been wrong before and I am sure I could be wrong again.
The bottom line.
Castile soap is lovely and natural. It can have a pH of between 9-11.5 in its natural state and you have limited scope to change that without changing the micelle structure of the product (based on my logic). Adding excess oil into the formula is something that many people choose to do to re-fat the skin as it is washed so as to avoid the skin being left feeling dry. This is acceptable but won’t change the pH.
So that’s that.
PS: Thanks to New Directions and especially to Alyce for helping with the experimental part of this piece.