If the diffusion coefficient D increases, what happens to the rate of moisture uptake in a laminate?

If the diffusion coefficient D increases, what happens to the rate of moisture uptake in a laminate?

• A. Moisture uptake rate increases.
• B. Moisture uptake rate decreases.
• C. Rate is unaffected.
• D. Diffusion stops.

Answer: (A)

Moisture movement in a laminate follows diffusion: how quickly it moves depends on how easily molecules can travel, captured by the diffusion coefficient. In Fickian diffusion, the moisture flux into the material is proportional to D times the moisture concentration gradient. So, for the same environmental humidity difference and geometry, increasing D increases the flux of moisture into the laminate. That means moisture enters faster, and the rate of uptake goes up. The time to reach a given moisture level also drops roughly with L^2/D, so a larger D shortens the charging time, especially at early stages. In short, higher diffusion coefficient speeds up how quickly moisture is absorbed.

Moisture movement in a laminate follows diffusion: how quickly it moves depends on how easily molecules can travel, captured by the diffusion coefficient. In Fickian diffusion, the moisture flux into the material is proportional to D times the moisture concentration gradient. So, for the same environmental humidity difference and geometry, increasing D increases the flux of moisture into the laminate. That means moisture enters faster, and the rate of uptake goes up. The time to reach a given moisture level also drops roughly with L^2/D, so a larger D shortens the charging time, especially at early stages. In short, higher diffusion coefficient speeds up how quickly moisture is absorbed.