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

我们的目的是通过研究迟滞现象来阐明纳米尺度木材细胞壁的结构。解释水吸附中的滞后现象是生物聚合物，特别是木材科学中一个长期存在的问题。近年来的研究对经典理论从可及羟基角度解释迟滞的能力提出了许多质疑。受新兴纳米多孔材料和吸附科学的启发，以及我们对滞后模式的初步研究，我们提出滞后是由吸附过程中水相变（细胞壁的毛细凝结和蒸发）中亚稳态的存在引起的。由于相变受细胞壁孔径的影响较大，通过物理模拟或模拟迟滞现象，可以揭示不同含水量下细胞壁孔径的分布。**我们将分实验、数学建模、蒙特卡罗分子模拟和细胞壁结构研究四个阶段进行研究。实验阶段包括系统的迟滞模式观察和材料表征。我们提出的迟滞机制将通过观察到的迟滞模式来检验。然后，在第二阶段，将建立一个数学模型来定量描述和预测扫描曲线。此外，对模型的性质和极限的讨论也有助于揭示迟滞的物理根源。第三阶段涉及模拟在细胞壁孔中吸附的水。在这一阶段，细胞壁将被视为具有均匀分布的圆柱形纳米孔的固体物质，并且简单的电位模型将用于细胞壁和水分子。在最后阶段，我们将使用第三阶段开发的模拟工具来探索细胞壁结构，如孔分布，细胞壁的能量异质，吸附水结构以及细胞壁与水的相互作用。**我们期望这项工作将使我们更好地理解细胞壁孔结构，以及细胞壁生物聚合物与水之间的相互作用，例如氢键网络的演化，以及水在细胞壁上的聚集等。我们还期望阐明的纳米级细胞壁结构为细胞壁的形成、变形和降解提供新的见解，并可能在性能和服务预测和优化方面应用。*这项研究将是我们最终目标的又一块砖，建立一个通用的木材模型，允许基于其解剖，化学和超微结构模拟其特性。********

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.********