氯化钠水溶液结构的研究

Study on the structure of sodium chloride aqueous solution

利用上海光源(SSRF)的第三代同步辐射光源测定室温下摩尔浓度分别为0.172 mol/L、0.343 mol/L、0.699 mol/L、1.064 mol/L、2.832 mol/L、3.910 mol/L、5.289 mol/L的NaCl水溶液的X射线散射数据.由X射线散射数据可知,随着NaCl水溶液浓度的增大,X射线散射曲线的特征峰由12.6°到13.4°发生偏移.运用Pair Distribution Function(PDF)理论对X射线散射数据进行处理,得到了不同浓度NaCl水溶液及纯水的差值对分布函数,其中的O-O峰随着浓度的增大逐渐分裂为两峰,O-O峰位在0.282 nm处.利用分子动力学模拟研究不同浓度的NaCl水溶液,表明Na+、Cl-的引入对水分子的氢键结构有一定的破坏,当浓度大于15%时,这种效果尤其明显. Na+、Cl-均存在两层水化层,各离子间配位数随浓度的增大而减少. H2O分子的自扩散系数远大于Na+和Cl-的自扩散系数,后两者的值随浓度的增大逐渐减少,Na+和Cl-的水化半径均随浓度增大而降低.

X-ray scattering data of NaCl aqueous solution was measured by the third generation synchrotron light source of Shanghai Synchrotron Radiation Facility(SSRF). The molar concentrations of the solution were 0.172 mol/L, 0.343 mol/L, 0.699 mol/L, 1.064 mol/L, 2.832 mol/L, 3.910 mol/L, 5.289 mol/L respectively at room temperature. Based on the X-ray scattering results, when the concentrations of NaCl aqueous solution increased, the characteristic peaks shifted from 12.6~o to 13.4~o. The pair distribution functions of NaCl aqueous solution with different concentrations and pure water were obtained by Pair Distribution Function(PDF) theory. The O-O peak gradually split into two peaks with the increased concentration and the O-O peak was at 0.282 nm. The results obtained by molecular dynamic simulation indicated that the hydrogen bond structure of water molecules was destroyed by Na^+ and Cl^-. The effect was particularly evident when the concentration was higher than 15%. It was found that there were two hydrated shells around Na^+ and Cl^-. The coordination number, the self-diffusion coefficient and the hydration radius all decreased with the increased concentration. The self-diffusion coefficient of water molecules was much higher than that of Na^+ and Cl^-.