I understand that there are several characteristics of curly hair which differ from straight hair (such as an asymmetrical distribution of disulphide bonds in curly hair), but really am struggling to understand the root cause of inherent curl on the macroscopic level.
My current understanding of the hair structure is based mostly upon this website
The most relevant part of the hair for our discussion is the cortex, which is made up of many axially aligned macrofibrils, or macroscopic keratin fibers, which are in some filler essentially of lipids/proteins. Inside these macrofibrils are microfibrils. These are also aligned axially and in some filler of lipids/ proteins. Inside the microfibrils are the protofibrils, even smaller fibers which are twisted around each other like a yarn. These protofibrils are made up of 4 keratin chains which are essentially twisted together and connected by disulphide bonds and hydrogen bonds. While hydrogen bonds are easily broken, the disulphide bonds are not. In curled hair, the macrofibril isn't symmetrical but I am unsure as to how this, or what other effects, actually lead to the curling.
I had previously assumed that the reason for curling is that in an asymmetrical configuration of the hair(IE not cylindrical but more oval in cross section), some residual stresses are formed by the disulphide bonds between the keratin, If this is true, it would lead me to believe that it would cause increased buckling of the protofibrils. But, even with straight hair and more symmetrical disulphide bonds, you already have some curling and buckling of the protofibrils, but the hair doesn't curl on a macroscopic level.
As such, it doesnt seem like this buckling due to asymetrical disulphide bonds would necessarily lead to a curled or organized structure on the macroscale, with the macrofibrils. This leads me to believe I am missing something.
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