NH_(4)Cl水溶液的结构和物性研究

Microstructure and Physical Properties of NH_(4)Cl Aqueous Solution

通过密度泛函理论(DFT)计算、拉曼光谱和同步辐射X射线散射法,研究了质量分数为1.0%~28.0%的NH_(4)Cl水溶液的微观结构。在室温下测量了粘度、接触角和电导率。由DFT计算和拉曼光谱结果可知,当溶质浓度升高至10.0%时,在2900 cm^(-1)和3100 cm^(-1)附近出现了明显的N-H作用峰,且随着质量分数的升高,NH_(4)Cl水溶液中的DDAA型氢键转变为DA和DAA型氢键。X射线散射结果表明,当NH_(4)Cl水溶液质量分数升高至10.0%时,差值对分布函数G(r)在0.298 nm附近出现明显双峰,表明在该浓度下溶液中NH_(4)^(+)-Cl^(-)接触离子对开始成为主要微观作用形式。NH_(4)Cl水溶液的粘度、接触角和电导率均随着NH_(4)Cl水溶液质量分数的增加而增大。NH_(4)Cl水溶液中氢键类型的转变、O-H...N键占比增多以及逐渐增加的NH_(4)^(+)-Cl^(-)接触离子是粘度和接触角变化的微观本质因素;电导率的增加与溶液中有效导电离子数量增加有关。

Density functional theory calculation(DFT),Raman spectroscopy and synchrotron radiation X-ray scattering were employed to study the microstructure of NH_(4)Cl solution with mass fraction of 1.0%~28.0%.Viscosity,contact angle and conductivity were measured at room temperature.From the results of DFT calculation and Raman spectroscopy,when the solute concentration increases to 10.0%,there are significant N-H peaks near 2900 cm^(-1)and 3100 cm^(-1),and with the increase of mass fraction,the double donor-double acceptor(DDAA)type hydrogen bonds in the NH_(4)Cl solution transform into the single donor-single acceptor(DA)and the single donor-double acceptor(DAA)type hydrogen bonds.X-ray scattering shows that the reduced pair distribution functions G(r)have a clear double peak near 2.98 when the mass fraction of aqueous NH_(4)Cl solution increases to 10.0%,indicating that the NH_(4)^(+)-Cl-contact ion pairs start to become the dominant microscopic interaction in the solution at this concentration.With the increase of the mass fraction of aqueous NH_(4)Cl solutions,the viscosity,contact angle and conductivity of aqueous NH_(4)Cl solution increase.The shift in the type of hydrogen bonding in aqueous NH_(4)Cl solutions,the O-H..N bonding occupancy,and the progressively increasing NH_(4)^(+)-Cl-contact ion pairs are the microscopic essential factors for the increased viscosity and contact angle with increasing solute concentration;the increase in conductivity is related to the increase in the number of effective conducting ions in the solution.