Non-Fickian diffusion in biomaterials

The knowledge of water vapour diffusion in materials is very important in several fields of application (drying, building materials, biofilms…). Regarding the drying process, the value of mass diffusivity, as well as its variations with moisture content, governs the second drying period, which is the most important in terms of drying time, energy consumption and product quality. In the case of biomaterials used for building insulation, this parameter is essential for transformation processes, including drying, but also for the proper design and use of buildings. Concerning biofilms, barrier properties are one of the most important physical properties of these materials to properly ensure a good end use. Nevertheless, experimental data of mass uptake of some biomaterials showed that did not follow the standard Fickian model. The precise determination of this non-Fickian behaviour showed to be a difficult task since the physical phenomena responsible for such behaviours depend on the biomaterial structure and physical properties. In particular, the abnormal macroscopic behaviour could result from the pore morphology (dual-scale effects), from the nano-structure, from the molecular reorganisation, or a combination of these spatial scales. This conference proposes a new methodology to quantify the non-Fickian diffusion. Based on a macroscopic formulation of coupled heat and mass transfer with kernel functions, the model parameters, intrinsic characteristic of the product of interest are determined by inverse analysis. Several complementary transient experiments can be analysed simultaneously, which insures the method robustness. Application examples are proposed for different products, including lignocellulosic materials and nanostructured biofilms.