The surface of glass quickly develops very small microcracks when exposed to high humidity. Although microcracks can be safely ignored in most applications, they can significantly decrease the mechanical strength of very small glass structures such as optical fibers. Consider a glass optical fiber of diameter Di = 125 µm that is coated with an acrylate polymer to form a coated fiber of outer diameter Do = 250 µm.
A telecommunications engineer insists that the optical fiber be stored in a low-humidity environment prior to installation so that it is sufficiently strong to withstand rough treatment by technicians in the field. If installation of a roll of fiber requires several hot and humid days to complete, will careful storage beforehand prevent microcracking? The mass diffusivity of water vapor in the acrylate is DAB = 5.5 X 10-13 m2/s while the glass can be considered impermeable.