1. A 1-mm-thick square (100 mm X 100 mm) sheet of polymer is suspended from a precision scale in a chamber characterized by a temperature and relative humidity of T = 300 K and = 0, respectively. Sud- denly, at time t = 0, the chamber's relative humidity is raised to = 0.95. The measured mass of the sheet increases by 0.012 mg over 24 h and by 0.016 mg over 48 h. Determine the solubility and mass diffusivity of water vapor in the polymer. Preliminary experiments have indicated that the mass diffusivity is greater than 7 X 10-13 m2/s.
2. A vitreous silica optical fiber of diameter 100 µm is used to send optical signals from a sensor placed deep inside a hydrogen chamber. The hydrogen is at a pres- sure of 20 bars.
(b) Determine the average hydrogen concentration and change in refractive index after 1 h and 10 h of operation in the hydrogen environment.