Isoelectric and isoionic points. Any chemist could help?

MariaGarciaMariaGarcia Member
in Hair
Hi!

Please, could someone explain to me the difference between isoelectric point and isoionic point? I know that the isoelectric point of hair occurs when the pH is 3.67 and the isoionic point when the pH is between 5.6 and 6.2, but I don't understand the difference between them (despite searching the internet), and how this affects the formulation of hair products (if it does).

I will appreciate your help.
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Comments

  • PharmaPharma Member, Pharmacist
    Under physiological conditions, the notion of 'isoelectric point' applies.
    However, what's you gain in knowing a hypothetical value (or rather a range, certainly not a fixed two decimal number)? As you can see HERE, chemical composition of hair depends on many variables and hence, the isoelectric point shifts all the times. It also depends on the site of the hair, how you treat you hair, age, and so on...
  • MariaGarciaMariaGarcia Member
    edited May 10
    That's because I'm studying (on my own) and I like to understand why things are done the way they are. In the text I'm reading it says that they are related to why conditioners are somewhat more acidic than shampoos, and the way cationic compounds bind to the hair fiber. Both are mentioned (isoelectric and isoionic), and I don't understand the difference between them, nor how they influence this (especially isoionic).
    Thank you very much, I will read the link you gave me, it sounds educational!
  • PharmaPharma Member, Pharmacist
    Isoionic is what you get in pure water, it's for most cases a hypothetical state. Isoelectric is closer to reality due to presence of counterions, other electrolytes, and pH active substances.
    The trick is to create enough binding opportunities, either by increasing the amount of negative charges on hair so that positive charged conditioning agents can electrostatically bind (like magnets of opposite poles attracting each other) or by increaseing surface. Someone here on board posted a link to a paper explaining how this actually works a few months ago. The problem with hair is that there are always positive and negative charges and these attract or reject each other. This results in higher or lower hydrophilicity/lipophilicity and accessibility/'swellability' of the 'layers' (constituted mostly of proteins and fatty acids).
    The different effects are working against each other and hence, there is no easy answer/solution. What seems to me as most favourable and which also reflects the prefered use of acidic conditioning is the denser structure of hair with 'layed down' keratin scales at low pH.
  • Thanks a lot, Pharma. How can you increase the surface of hair? This is a new concept for me...
  • PharmaPharma Member, Pharmacist
    It's not the surface you see but the one in between molecular layers; you'd have to be a water molecule or similar to see it. A bit like a slice of cream cake where the puff paste is the hair and the vanilla cream the conditioner, the closer the paste layers to each other, the less cream... sort of... :smiley:
  • I see... And... how do you get that? Is this the role of hydrolyzed proteins, silicones, lipids, etc, or are these just the cream of the cake, and is some additional mechanism needed to increase surface area and make room for them?

    I'll try to find the link you mentioned. I do not know if with these data I will be easy to find, if you remember any clue about the title or the content I will thank you.

    (I love your explanations. For someone with a graphic mind like mine, they are perfect)
  • PharmaPharma Member, Pharmacist
    The mentioned effect is mostly driven by pH ;) .
    Uh... key words???? 'Conditioner' is all I remember LoL (sorry)!
  • Hahaha, don't worry, you've been very helpful, and you've piqued my curiosity even more :p . Also, searching the link you mention, I am finding a lot of interesting questions, for example how colloidal gels formed by an anionic surfactant and a fatty alcohol penetrate the hair and strengthen it.

    Thank you very much!  ;) <3
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