A Mechanical Model of Overnight Hair Curling
TLDR Longer time setting curls overnight leads to better curl retention.
The study developed a mechanical model to understand how straight hair can be temporarily curled overnight using hair rollers. It investigated the impact of various factors on how well curls hold, such as the size of the hair roller compared to the hair, the amount of stretch in the hair, the time the hair is left to set (creep time), the hair's Poisson's ratio, and the effect of gravity. The study concluded that the key factor for maintaining curls is the creep time, with longer times leading to better curl retention. The influence of hair thickness and the tension applied during the curling process were found to be minimal. The model's predictions were confirmed by both a theoretical model and practical overnight curling experiments. The experiments, which were conducted on Asian hair samples for 10 hours, showed that hair fixatives could help maintain the curls for a day or more. However, gravity was found to negatively affect curl retention for longer hair. The study's findings were supported by the National Natural Science Foundation of China, DARPA, and AFOSR.