Wormlike Micelles of a Cationic Surfactant in Polar Organic Solvents: Extending Surfactant Self-Assembly to New Systems and Subzero Temperatures.,Langmuir

当前位置： X-MOL 学术 › Langmuir › 论文详情

Our official English website, www.x-mol.net, welcomes your feedback! (Note: you will need to create a separate account there.)

Wormlike Micelles of a Cationic Surfactant in Polar Organic Solvents: Extending Surfactant Self-Assembly to New Systems and Subzero Temperatures.
Langmuir ( IF 3.7 ) Pub Date : 2019-09-17 , DOI: 10.1021/acs.langmuir.9b02125
Niti R Agrawal ₁ , Xiu Yue _{1,

2} , Yujun Feng ₃ , Srinivasa R Raghavan ₁

Affiliation

Wormlike micelles (WLMs) are long, flexible cylindrical chains formed by the self-assembly of surfactants in semidilute solutions. Scientists have been fascinated by WLMs because of their similarities to polymers, while at the same time, the viscoelastic properties of WLM solutions have made them useful in a variety of industrial applications. To date, most studies on WLMs have been performed in water (i.e., a highly polar liquid), while there are a few examples of "reverse" WLMs in oils (i.e., highly nonpolar liquids). However, in organic solvents with lower polarity than water such as glycerol, formamide, and ethylene glycol, there have been no reports of WLMs thus far. Here, we show that it is indeed possible to induce a long-tailed cationic surfactant to assemble into WLMs in several of these solvents. To form WLMs, the surfactant is combined with a "binding" salt, i.e., one with a large organic counterion that is capable of binding to the micelles. Examples of such salts include sodium salicylate and sodium tosylate, and we find self-assembly to be maximized when the surfactant and salt concentrations are near-equimolar. Interestingly, the addition of a simple, inorganic salt such as sodium chloride (NaCl) to the same surfactant does not induce WLMs in polar solvents (although it does so in water). Thus, the design rules for WLM formation in polar solvents are distinct from those in water. Aqueous WLMs have been characterized at temperatures from 25 °C and above, but few studies have examined WLMs at much lower (e.g., subzero) temperatures. Here, we have selected a surfactant with a very low Krafft point (i.e., the surfactant does not crystallize out of solution upon cooling due to a cis-unsaturation in its tail) and a low-freezing solvent, viz. a 90/10 mixture of glycerol and ethylene glycol. In these mixtures, we find evidence for WLMs that persist down to temperatures as low as -20 °C. Rheological techniques as well as small-angle neutron scattering (SANS) have been used to characterize the WLMs under these conditions. Much like their aqueous counterparts, WLMs in polar solvents show viscoelastic properties, and accordingly, these fluids could find applications as synthetic lubricants or as improved antifreezing fluids.

中文翻译：

极性有机溶剂中阳离子表面活性剂的蠕虫状胶束：将表面活性剂的自组装扩展到新系统和零以下温度。

蠕虫状胶束（WLM）是由半稀释溶液中表面活性剂的自组装形成的长而柔软的圆柱状链。WLM与聚合物的相似之处使科学家着迷，同时WLM解决方案的粘弹性也使其在各种工业应用中有用。迄今为止，大多数有关WLM的研究都是在水（即高极性液体）中进行的，而在油（即非极性高液体）中有“反向” WLM的一些例子。但是，在甘油，甲酰胺和乙二醇等极性比水低的有机溶剂中，迄今没有关于WLM的报道。在这里，我们表明确实有可能在这些溶剂中的几种中诱导长尾阳离子表面活性剂组装成WLM。要形成WLM，表面活性剂与“结合”盐结合，即具有能够与胶束结合的大有机抗衡离子的盐。这样的盐的例子包括水杨酸钠和甲苯磺酸钠，并且当表面活性剂和盐的浓度接近等摩尔时，我们发现自组装被最大化。有趣的是，将简单的无机盐（例如氯化钠（NaCl））添加到相同的表面活性剂中不会在极性溶剂中引起WLM（尽管在水中也是如此）。因此，在极性溶剂中形成WLM的设计规则不同于在水中的规则。水性WLM在25°C以上的温度下具有特征，但是很少有研究在较低（例如，零以下）温度下检测WLM。在这里，我们选择了Krafft点非常低的表面活性剂（即，表面活性剂在冷却后不会因溶液中的结晶而结晶，这是由于其尾部为顺式不饱和键）和一种低冷冻度的溶剂，即。甘油和乙二醇的90/10混合物。在这些混合物中，我们发现WLM可以在低至-20°C的温度下持续存在的证据。在这些条件下，流变技术以及小角度中子散射（SANS）已用于表征WLM。极性溶剂中的WLM与其水性对应物非常相似，显示出粘弹性，因此，这些流体可以用作合成润滑剂或改进的抗冻剂。我们发现WLM可以在低至-20°C的温度下持续存在的证据。在这些条件下，流变技术以及小角度中子散射（SANS）已用于表征WLM。极性溶剂中的WLM与其水性对应物非常相似，显示出粘弹性，因此，这些流体可以用作合成润滑剂或改进的抗冻剂。我们发现WLM可以在低至-20°C的温度下持续存在的证据。在这些条件下，流变技术以及小角度中子散射（SANS）已用于表征WLM。极性溶剂中的WLM与其水性对应物非常相似，显示出粘弹性，因此，这些流体可以用作合成润滑剂或改进的抗冻剂。

更新日期：2019-09-18

点击分享查看原文

点击收藏

阅读更多本刊新发论文本刊介绍/投稿指南