Ion fluctuations and intermembrane interactions in the aqueous dispersions of a dialkylchain cationic surfactant studied using dielectric relaxation spectroscopy and small- and wide-angle X-ray scattering
Ion fluctuations and intermembrane interactions in the aqueous dispersions of a dialkylchain cationic surfactant studied using dielectric relaxation spectroscopy and small- and wide-angle X-ray scattering
复制标题
使用介电弛豫光谱和小角和广角 X 射线散射研究二烷基链阳离子表面活性剂水分散体中的离子波动和膜间相互作用
DOI：
10.1039/c8cp05575k
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发表时间：
2018
影响因子：
3.3
通讯作者：
Sato Takaaki
中科院分区：
文献类型：
--
作者：
Yanase Keiichi;Obikane Miku;Ogura Taku;Buchner Richard;Igarashi Akinori;Sato Takaaki
二烷基链阳离子表面活性剂在水中形成所谓的α-凝胶，几乎没有流动性，加入少量盐后转化为高度流体分散体。这种有趣的现象在家庭工业中得到了利用。然而，其潜在机制仍不清楚。在这里，我们使用介电弛豫光谱（DRS）和同时小角和广角X射线散射（SWAXS）来阐明这个问题。我们发现，过量的CaCl 2诱导α-凝胶到多层囊泡（MLV）的转变伴随着储层体积分数的显着增加。这类似于未结合的片层到结合的片层转变，如果不引起弱的长程静电吸引力，就无法解释这种转变。DRS数据提供的证据表明，抗衡离子在界面处的垂直和横向波动，其弛豫幅度急剧依赖于水相的结晶状态。体积水幅度非常小，可能反映了由MLV结构引起的去极化电场，沿着真正的水合作用。SAXS强度的改良Caillé方法揭示了敏感的盐浓度依赖性膜-膜相互作用。在盐浓度约为0.0001时，形成的膜起伏最小。10 mmol L−1。当浓度超过25 mmol L−1时，膜表面的分离度很小（<2.5 nm），产生的波动比Helfrich相互作用所预测的要大得多。这表明，水合力，通常认为，诱导强烈的短程排斥，不抑制膜波动波动。
A dialkylchain cationic surfactant forms the so-called α-gel in water showing virtually no fluidity, which is transformed into a highly fluidic dispersion upon addition of a small amount of salt. This intriguing phenomenon is utilized in household industries. However, the underlying mechanisms remain unclear. Here, we use dielectric relaxation spectroscopy (DRS) and simultaneous small- and wide-angle X-ray scattering (SWAXS) to shed light on this issue. We find that an excess amount of CaCl2 induces an α-gel-to-multi-lamellar vesicle (MLV) transition accompanied by a marked increase of the reservoir volume fraction. This resembles an unbound lamellar-to-bound lamellar transition that cannot be explained without invoking a weak long-ranged electrostatic attraction. The DRS data provide evidence that the counterions fluctuate both vertically and laterally at the interface, whose relaxation amplitudes sharply depend on a percolating state of an aqueous phase. The strikingly small bulk-water amplitude is likely to reflect depolarizing electric fields induced by the MLV architecture, along with genuine hydration effects. The modified Caillé approach to the SAXS intensities reveals sensitive salt-concentration dependent membrane–membrane interactions. The least undulating membranes are formed at a salt concentration of ca. 10 mmol L−1. Above 25 mmol L−1, where small surface separation (<2.5 nm) is attained, far more undulating membranes than those predicted by the Helfrich interaction are produced. This suggests that the hydration forces, generally believed to induce strong short-range repulsion, do not suppress the membrane undulation fluctuations.