With a view toward the application of highly hygroscopic polymers as a humidity responsive self-actuator, the evaluation of the real time moisture concentration in the material becomes a priority. In this paper, the moisture diffusion process in a cellulose acetate (53.3% of acetylation) has been studied. Membranes of cellulose acetate (thickness within the range 66–200 µm) have been prepared, and the moisture absorption at room temperature and at a different relative humidity (RH within the range 21–53%) has been monitored. An analytical model has been used to describe the observed non-Fickian sigmoidal behavior of moisture diffusion. A relaxation factor (β) of about 0.026 s⁻¹ and a moisture diffusion coefficient (D) of 3.35 × 10^–6 mm²/s have been determined. At constant room temperature, the moisture concentration at saturation (C_sat) has shown a linear relation with relative humidity. The identified values β, D and C_sat of the analytical model have been used as input for the finite element simulation of the non-Fickian diffusion. The reliability of the finite element simulations has been confirmed with a second set of experiments.

考虑到高吸湿性聚合物作为湿度响应自致动器的应用，材料中实时水分浓度的评估成为当务之急。在本文中，研究了醋酸纤维素（乙酰化 53.3%）中的水分扩散过程。已经制备了醋酸纤维素膜（厚度在 66-200 µm 范围内），并监测了室温和不同相对湿度（RH 范围为 21-53%）下的吸湿性。分析模型已用于描述观察到的水分扩散的非 Fickian sigmoidal 行为。约 0.026 s ^-1的松弛因子 (β)和 3.35 × 10 ^–6 mm ²的水分扩散系数 (D)/s 已确定。在恒定室温下，饱和水分浓度 (C _sat ) 与相对湿度呈线性关系。分析模型的识别值 β、D 和 C _sat已用作非 Fickian 扩散的有限元模拟的输入。第二组实验证实了有限元模拟的可靠性。