The Effect of Relative Humidity on the Spreading of Ethanol on Human Hair Fibers

In the 1972 study by R. W. Rance, the spreading behavior of ethanol on human hair fibers was examined under different relative humidity (RH) conditions. It was found that at a low RH of 10%, ethanol fully wetted the hair fibers, creating unduloid shapes consistent with Bondarenko's theory, and these shapes remained until the ethanol completely evaporated. However, at 50% RH, although ethanol initially wetted the fibers, the contact angle increased over time, indicating a decrease in wettability. This was attributed to water condensing on the evaporating ethanol drop, rather than changes in the hair's critical surface tension due to humidity. The study concluded that ethanol's wettability on hair fibers is high at low RH but decreases at higher RH as water condensation occurs. The number of hair fibers tested was not mentioned in the study.