Contamination in Sodium Dodecyl Sulfate Solutions: Insights from the Measurements of Surface Tension and Surface Rheology
Contamination in Sodium Dodecyl Sulfate Solutions: Insights from the Measurements of Surface Tension and Surface Rheology
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DOI：
10.1021/acs.langmuir.2c00460
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发表时间：
2022-05-31
期刊：
影响因子：
3.9
通讯作者：
Razavi, Sepideh
中科院分区：
文献类型：
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作者：
Correia, Elton L.;Brown, Nick;Razavi, Sepideh
众所周知，十二烷基硫酸钠（SDS）溶液中以十二醇（LOH）形式存在的污染会极大地影响所产生的界面性质，如表面张力（SFT）和流变性。十二醇分子是SDS水解的产物，固有地存在于SDS溶液中，与SDS相比，十二醇分子具有更高的表面活性，因为它们不易溶于水。在SFT等温线上的特征下降是样品中十二醇污染的指示。溶液中电解质的存在会影响SDS的表面活性及其临界胶束浓度，并可能产生与纯SDS样品非常接近的SFT等温线。在这种情况下对等温线的解释可能导致对表面纯度的错误解释。在这项工作中，我们研究了在没有电解质和存在电解质的情况下SDS溶液的SFT等温线。我们将等温线拟合到三种不同的热力学吸附模型中，以估计样品中十二醇的含量。我们在双组分流变模型中应用LOH含量的估计值来预测这种表面活性剂负载表面的粘弹性。我们将这些结果与实验测量的界面流变性能进行了比较。我们的研究结果表明，即使对于含有背景电解质的溶液，杂质的存在也可以在动态膨胀和收缩下被捕获。
The presence of contamination in sodium dodecyl sulfate (SDS) solutions in the form of dodecanol (LOH) is known to drastically affect the resulting interfacial properties such as surface tension (SFT) and rheology. Dodecanol molecules, which are the product of SDS hydrolysis and are inherently present in SDS solutions, have higher surface activity compared to SDS because they are less soluble in water. A characteristic dip in the SFT isotherm is an indicator of the dodecanol contamination in the sample. The presence of an electrolyte in the solution impacts the surface activity of SDS and its critical micelle concentration, and could yield SFT isotherms that closely match those obtained for pure SDS samples. The interpretation of the isotherms in such cases could thus lead to misinterpretation of the surface purity. In this work, we have examined the SFT isotherms for SDS solutions in both the absence and presence of electrolyte. We have fitted the isotherms to three different thermodynamic adsorption models to estimate the amount of dodecanol present in the sample. We have applied the estimated values for the LOH content in a two-component rheological model to predict the viscoelasticity of such surfactant-laden surfaces. We have compared these results with the experimentally measured interfacial rheological properties. Our findings demonstrate that the presence of impurities can be captured under dynamic expansion and contractions, even for solutions containing background electrolyte.