Hypothesis

Some low molecular weight additives can strongly influence the phase behavior of aqueous surfactant systems, and this offers an important handle to control the properties of surfactant solutions and thus to optimize the stability and performance of various formulations.

Experiments

The surfactant dioctadecyldimethylammonium chloride (DODAC) self-assembles into two lamellar phases in water, the gel phase (L_β) and the liquid crystalline phase (L_α). Here, we present approaches to tune the gel-to-liquid crystalline transition temperature (T_m) with the use of additives. The effects of urea, sodium butyrate and butyric acid on the packing behavior of DODAC were determined. The surfactant phases were characterized using polarized optical microscopy (POM), differential scanning calorimetry (DSC), and small/wide angle X-ray scattering (SWAXS).

Findings

All three additives - urea, sodium butyrate and butyric acid yield a single and stable lamellar phase. Urea and sodium butyrate have only minor effects on T_m, butyric acid gives a large decrease as it stabilizes the L_α phase with respect to the L_β phase. From the bilayer thickness of the gel phase an interdigitated or tilted packing of the surfactant molecules is suggested. The addition of sodium butyrate gives a highly interdigitated gel structure and resulted in the transition from lamellar liquid crystal to an isotropic L₃ phase.

中文翻译：

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阐明添加剂对双尾阳离子表面活性剂烷基链堆积的影响

假设

某些低分子量添加剂会强烈影响水性表面活性剂体系的相行为，这为控制表面活性剂溶液的性能并因此优化各种配方的稳定性和性能提供了重要的手段。

实验

所述表面活性剂十八烷基氯化铵（DODAC）自组装成在水中2个层状相，所述凝胶相（L _β）和液晶相（L _α）。在这里，我们介绍了使用添加剂来调整凝胶到液晶的转变温度（T _m）的方法。确定了尿素，丁酸钠和丁酸对DODAC堆积行为的影响。使用偏振光学显微镜（POM），差示扫描量热法（DSC）和小/广角X射线散射（SWAXS）表征表面活性剂相。

发现

三种添加剂-尿素，丁酸钠和丁酸均可产生单一且稳定的层状相。尿素和丁酸钠具有对T只有轻微的影响_米，丁酸给出大的下降，因为它稳定为L _α相对于与L _β相。从凝胶相的双层厚度，提出了表面活性剂分子的指状或倾斜堆积。丁酸钠的添加产生高度相互交叉的凝胶结构，并导致从层状液晶到各向同性的L ₃相的转变。