Final answer:
The reduction reaction in permanent waving involves breaking disulfide bonds within the hair's keratin structure using ammonium thioglycolate, enabling the hair to take on a new shape around rollers. After reshaping, an oxidizing agent, commonly hydrogen peroxide, is applied to reform the disulfide bonds, fixing the new curls in place. This chemical process differs from temporary waving, which only physically alters hair shape through disruption of hydrogen bonds by water.
Step-by-step explanation:
The reduction reaction in permanent waving of hair occurs when a reducing agent, typically ammonium thioglycolate, is applied to the hair. This chemical disrupts the disulfide bonds within the hair's keratin structure. These disulfide bonds are responsible for the strength and shape of the hair, linking different protein chains and loops within the keratin.
During the permanent wave process, hair is first wrapped around rollers or curlers. The reducing agent then breaks some disulfide bonds, which allows the hair's alpha-helices to shift positions relative to each other. As a result, the hair can take on the shape of the rollers or curlers. After the reduction reaction, an oxidizing agent, such as a dilute solution of hydrogen peroxide, is applied. This agent is referred to as the 'neutralizer,' and its role is to reform the disulfide bonds in their new positions. The reformation of these bonds by oxidation ensures the hair retains the new curls as it dries.
In contrast, a temporary wave involves a physical change rather than a chemical one. Wet hair can have its hydrogen bonds temporarily disrupted by water molecules, allowing the strands to take on a new shape that holds until the hair is wetted again.
The entire process of permanent waving demonstrates the redox chemistry, where reduction and oxidation reactions work hand in hand to achieve a lasting change. The addition of hydrogen to the hair during the reducing step and the removal of hydrogen or the addition of oxygen during the oxidizing step are classic examples of redox reactions.