Sorption Hysteresis Modeling: a New Step toward the Understanding of Cell Wall Architecture

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We aim to elucidate the nanoscale wood cell-wall architecture by studying the hysteresis phenomenon. Explaining the hysteresis phenomenon in water sorption is a long-standing problem in biopolymer and in particular, wood science. Recent studies cast a lot of doubts on ability of classical theories to explain hysteresis in terms of accessible hydroxyls. Inspired by emerging nanoporous materials and sorption science, and our preliminary investigation on hysteresis patterns, we propose that the hysteresis is caused by the existence of metastable states taking place in water phase transitions (capillary condensation and evaporation in cell-walls) during the sorption process. Because the phase transition is highly affected by cell-wall pore sizes, by physically modeling or simulating hysteresis, we may reveal the cell-wall pore size distribution under different moisture contents. **We will conduct this research in four phases: experimental, mathematical modeling, Monte Carlo molecular simulation, and cell-wall structure investigation. The experimental phase includes systematic hysteresis patterns observations and material characterization. Our proposed hysteresis mechanism will be examined by observed hysteresis patterns. Then, in phase two, a mathematical model will be developed to describe and predict the scanning curves quantitatively. Furthermore, discussion of the properties and limit of the model will also help reveal physical origin of hysteresis. The third phase involves simulation of water adsorbed in cell-wall pores. In this phase, cell-walls will be considered as solid substances with uniformly distributed cylinder nanopores, and simple potential models will be used for both cell-walls and water molecules. In the last phase, we will use the simulation tool developed in phase three to explore cell-wall structures such as pore distribution, energy heterogeneous of cell-walls, adsorbed water structure and interaction of cell-wall and water. **We expect that this work will bring us toward a better understanding of cell-wall pore structures, and interaction between cell-wall biopolymers and water, e.g. evolution of hydrogen bounding networks, and clustering of water on cell-walls etc. We also expect the elucidated nanoscale cell-wall structure to provide new insights into cell-wall formation, deformation and degradation with possible applications in property and service prediction and optimization.*This research will be another brick towards our ultimate goal, the building of a universal wood model that will allow the simulation of its properties based on its anatomy, chemistry and ultrastructure.********