Abstract:

Diffusion processes play a critical role in the response of actuating materials where solvent absorption induces expansion or contraction of the material matrix. While Fickian diffusion has traditionally been used to model such process, it is often inadequate for describing non-Fickian diffusion behaviors observed in materials like polymers and tracing paper. This research proposes using the Onsager principle as a more general framework to address the limitations of Fickian diffusion models. By minimizing the Rayleighian function, the Onsager principle incorporates mechanical, drag, and viscous forces to accurately predict solvent transport and actuation in materials. A study performed on tracing paper was used to test the validity of this approach. Preliminary results demonstrate that the model based on the Onsager principle provides precise descriptions of non-Fickian diffusion, as evidenced in the bending behavior of the tracing paper.

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