吸着水对木材几乎所有物理力学性能有着显著影响。相比于常温常压下体态水，木材中吸着水流动性减弱、凝固点和能量态都降低。项目采用分子模拟方法研究木材细胞壁孔隙所构成的纳米受限环境下吸着水结构及相变，从分子层面揭示吸着水特殊性质的内在机理。基于模拟所得热力学平衡态时水分子的空间位置，计算水分子中氧原子横向密度分布、氧-氧原子径向分布及分子间氢键角度分布函数，定量分析吸着水结构，尤其是可结冰吸着水的冰相结构。分析模拟的吸着水密度、能量随温度或相对湿度的变化，探索吸着水固液及气液相变临界点、相变性质（一级/二级相变）和临界温度。模拟中系统调节细胞壁孔径和孔壁亲水性，构建温度—细胞壁孔径的相图，探索纳米受限环境对吸着水结构及相变的影响。基于水分吸附等温线和差示扫描量热曲线所得热力学函数，优化模拟中势能参数，提高模拟可靠性。本研究能丰富木材吸附、传质理论，为吸着水、改性剂等在细胞壁中的迁移提供科学依据。

Bound water has a significant effect on almost all physical and mechanical properties of wood. Compared with the bulk water at room temperature and pressure, the bound water in wood has reduced mobility, lowered freezing point, and reduced energy states. Molecular simulations have been proposed to study the structure and phase transition of bound water confined in wood cell wall pores, revealing the underlying mechanisms of the unusual properties of bound water at the molecular level. Water structures, especially the ice structure from the freezable bound water, will be quantitatively analyzed through functions such as transverse distributions of the density of oxygen atoms in water, and oxygen-oxygen radial distributions, and hydrogen bond angle distributions. The critical point of the solid-liquid and vapor-liquid phase transitions of bound water, the properties of these transitions (first-order/second-order phase transitions), and the critical temperature will be evaluated by analyzing how the modeled density and energy of bound water change with the temperature or the relative humidity. The effects of the nano-confined environment on the structure and phase transition of bound water will be explored by systematically adjusting the cell wall pore size and the hydrophilicity of the pore walls in the simulations, and constructing a phase diagram of temperature-cell wall pore size. The interaction energy parameters in molecular simulations will be optimized to improve the reliability of the simulations based on the thermodynamic functions predicted from the experimental water sorption isotherms and differential scanning calorimetry curves. The proposed study is expected to enrich the wood sorption and mass transfer theories, and provide a scientific basis for the transfer of bound water and modifiers in the cell walls.