Wikipedia:Reference desk/Archives/Miscellaneous/2021 December 1

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December 1

Hair conditioner

I don't understand what this section is saying can someone help me understand this please.

pH Conditioners are frequently acidic, as low pH protonates the keratin's amino acids. The hydrogen ions give the hair a positive charge and create more hydrogen bonds among the keratin scales, giving the hair a more compact structure. Organic acids such as citric acid are usually used to maintain acidity.

https://en.wikipedia.org/wiki/Hair_conditioner#pH115.64.124.152 (talk) 18:21, 1 December 2021 (UTC)

So, you need to understand what an acid is and what pH tells you about a substance's acidity. In terms that make sense for this discussion, an acid is a substance that will, when it interacts with other substances, donates a positively-charged hydrogen ion, symbolically represented as H⁺ (this is known as the Bronsted-Lowry definition of acids). H⁺ ions are often called protons, because that's what they are; a hydrogen atom consists of one negative electron and one positive proton. if you ionize that atom by removing the only electron it has, you're just left with a proton. So, the process by which an acid gives its H⁺ ion to other substances is known as "protonation". We say that the acid "protonates" other substances. Stronger acids (ones that are more likely to give H⁺ ions to other substances) have a LOW pH. So, the sentence is saying that because conditioners have a low pH, they are acids. And because they are acids they protonate (give H⁺ ions) to the keratin in your hair. This accumulation of H⁺ ions by your hair has some complicated effects, but the general idea is that those effects tend to cause the strands of the hair to become more "compact". Basically, your hair is made of scales of keratin (see this image) and these extra "hydrogen bonds" pull those scales in closer, making each strand smoother and more compact, which is sort of what you want conditioner to do. Let me know if that helps and if you have any more questions. --Jayron32 18:44, 1 December 2021 (UTC)

Hair is scaly under a microscope

Electrostatic forces stick things together

Executive summary with illustrations: hair is rough and scaly. Sticking the scales down flat makes it smooth. Static charge makes things stick together. Acids give molecules a charge.  Card Zero  (talk) 19:02, 1 December 2021 (UTC)

I like your explanation even better than mine. --Jayron32 19:16, 1 December 2021 (UTC)

The "complicated effects" you mentioned are probably important, though. Particularly to the matter of why the scales stick to the hair but the entire hair doesn't stick to all the other hairs, which would be a suboptimal hair condition.  Card Zero  (talk) 19:47, 1 December 2021 (UTC)

The complicated effects has to do with how amino acids (the building blocks of proteins like keratin) behave in different pH environments. Depending on the pH of the environment, these amino acids will interact with each other differently; for example something like aspartic acid will behave as a negative ion at higher pHs (including at physiological pH), but at lower pH, the ion gets protonated, so it behaves as a polar-covalent molecule, and can now participate in "hydrogen bonding", which the ion cannot. I suspect, but don't know exactly, that this is the mechanism described in the original article. --Jayron32 19:55, 1 December 2021 (UTC)