无机盐阳离子对十二烷基硫酸钠表面活性剂降低水的表面张力效果的机理研究

Mechanism study on the effect of inorganic salt cations on the effect of sodium dodecyl sulfate surfactant on reducing the surface tension of water

采用真球气泡法测定了不同价态(Na^(+)、Cu^(2+)、Fe^(3+))和浓度的无机盐体系下十二烷基硫酸钠(SDS)表面活性剂溶液的表面张力、表面扩展黏度和临界胶束浓度(cmc),加入无机盐之后,SDS的cmc值由8 mmol/L降至3 mmol/L,达到最低表面张力的SDS浓度值(C_(t))和最大表面扩展黏度时的SDS浓度值(C_(v))均小于未添加时对应的SDS浓度,且Ct=Cv=cmc=3 mmol/L。在cmc值时,溶液表面张力为37.29 mN/m,加入NaCl后溶液表面张力为27.53 mN/m;加入CuCl_(2)后溶液表面张力为23.44 mN/m;加入Fe(NO_(3))_(3)后溶液表面张力为21.35 mN/m。在cmc值时,溶液的表面扩展黏度为1.70 mN·s/m,加入NaCl后溶液扩展黏度为2.21 mN·s/m;加入CuCl_(2)后溶液扩展黏度为2.58 mN·s/m;加入Fe(NO_(3))_(3)后溶液扩展黏度为2.75 mN·s/m。阳离子的加入使得SDS降低水的表面张力值的效果增强,文章定义M(表面活性剂溶液表面张力值变化的指标)去判断无机盐阳离子对于SDS溶液的作用效果,并分析验证SDS分子呈长条形结构,推定无机盐阳离子提高SDS降低水表面张力值作用效果的机理为:负电荷在SDS分子的纵截面的顶部,阳离子通过正电荷吸引SDS的负电荷端,使得纵截面横躺在溶液表面,增加了SDS分子在表面的覆盖面积,从而增大了SDS降低水的表面张力值的作用效果。

The surface tension,surface extension viscosity and critical micelle concentration(cmc)of sodium dodecyl sulfate(SDS)surfactant solution in inorganic salt systems with different valence states(Na+,Cu2+,Fe3+)and concentrations were determined by the true spherical bubble method,after adding inorganic salt,the cmc value of SDS decreased from 8 mmol/L to 3 mmol/L,the SDS concentration value(C_(t))at the lowest surface tension and the SDS concentration value at the maximum surface extended viscosity(Cv)were both lesser than the corresponding SDS concentration when it is not added,and Ct=Cv=cmc=3 mmol/L.At the cmc value,the surface tension of the solution is 37.29 mN/m,and the surface tension of the solution after adding NaCl is 27.53 mN/m;after adding CuCl_(2),the surface tension of the solution is 23.44 mN/m;adding Fe(NO_(3))_(3),the surface tension of the solution was 21.35 mN/m.At the cmc value,the surface extension viscosity of the solution is 1.70 mN·s/m,the solution extension viscosity after adding NaCl is 2.21 mN·s/m,and the solution extension viscosity after adding CuCl_(2) is 2.58 mN·s/m;after adding Fe(NO3)3,the extended viscosity of the solution is 2.75 mN·s/m.The addition of cations enhances the effect of SDS on reducing the surface tension value of water.This paper defines M(an indicator of the change of surface tension value of surfactant solution)to judge the effect of inorganic salt cations on SDS solution,and analyze and verify that SDS molecules are long strips.It is inferred that the mechanism of the effect of inorganic salt cations on improving the effect of SDS on reducing the surface tension value of water is as follows:the negative charge is at the top of the longitudinal section of the SDS molecule,and the cation attracts the negatively charged end of SDS through the positive charge,so that the longitudinal section is lying on the surface of the solution,increasing the coverage area of SDS molecules on the surface,thereby increasing the effect of SDS on reducing the surface tension value of water.