Which factor primarily dictates how quickly moisture diffuses through a laminate?

• A. Applied mechanical load.
• B. The diffusion coefficient D.
• C. Initial moisture content.
• D. Layer thickness only.

Answer: (B)

Moisture moves through a laminate according to diffusion, and the speed of that diffusion is set by the diffusion coefficient D. This parameter encapsulates how easily water molecules can move through the polymer matrix—it's a material property that directly controls how fast the concentration profile changes. A larger D means faster diffusion for the same concentration gradient, while a smaller D slows things down.

Initial moisture level affects the driving force (the gradient) and can change the initial flux, but it does not establish the rate at which diffusion proceeds. The applied mechanical load isn’t the primary control on diffusion rate in the standard diffusion picture. Layer thickness matters for the total time to diffuse across the laminate (the time roughly scales with thickness squared for a given D), but it’s a geometric factor rather than the intrinsic rate-determining property. In a laminate with multiple layers, the overall rate is governed by the effective diffusion behavior, but the diffusion coefficient remains the key factor setting how quickly moisture moves.