聚丙烯酰胺稀溶液的分子模拟

Molecular Simulation of Dilute Polyacrylamide Solutions

聚丙烯酰胺(PAM)是一类重要的线性水溶性聚合物,具有"百业助剂"之称,因此对其溶液性质的研究意义重大.在溶液质量浓度约为1g·mL-1的基础上,分别构建了含有不同水分子数的溶液模型.采用分子动力学(MD)方法模拟分析了不同温度下非离子型的聚丙烯酰胺(PAM-H)和阴离子型的聚丙烯酰胺(HPAM)在纯水溶液及含不同质量分数NaCl的水溶液中的回旋半径(Rg).结果发现,不同温度下PAM-H和HPAM的抗盐性能的模拟结果与实验数据基本吻合,水分子数不同的溶液模型所得模拟结果趋势没有明显变化,为了提高模拟效率,选取含有2000个水分子的溶液模型分析HPAM链中氧负离子及氧原子的径向分布函数,从微观结构模拟说明了HPAM水溶液粘度随NaCl质量分数增加而减小,且HPAM比PAM-H具有较好的增粘效果及较差的抗盐性能的原因.

Polyacrylamide （PAM） applied to various fields is an important class of linear water-soluble polymers. Therefore, it is of great significance to study the solution properties of PAM. We constructed solution models containing different amounts of water molecules with a mass concentration of about 1 g·mL-1. Using molecular dynamics （MD） simulations we calculated the radius of gyration （Rg） for non-ionic PAM （PAM-H） and anionic PAM （HPAM） in pure water and in aqueous solutions with different mass fractions of NaCl. We discussed their behaviors at different temperatures. We found that the salt tolerance of the polyacrylamides from the simulation agreed with the experimental results at different temperatures. Furthermore, the simulation results for all the solution models containing a different amount of water molecules basically showed a similar trend. Considering computational efficiency, the solution model containing 2000 water molecules was selected for our study. The radial distribution functions （RDF） for the oxygen ions and oxygen atoms of the HPAM chain were investigated in NaCl solution model containing 2000 water molecules. The reduced viscosity of HPAM solutions with increasing NaCl mass fractions and a better thickening ability as well as poor salt tolerance compared to PAM-H were explained considering their microstructures as determined by RDF.