Bending elasticity of charged surfactant layers:: The effect of layer thickness
Bending elasticity of charged surfactant layers:: The effect of layer thickness
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DOI：
10.1021/la052800z
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发表时间：
2006-04-11
期刊：
影响因子：
3.9
通讯作者：
Bergström, LM
中科院分区：
文献类型：
--
作者：
Bergström, LM
从理论上研究了有限厚度带电单组分表面活性剂薄膜的弯曲特性。结果表明，对于具有柔性疏水尾部的离子表面活性剂形成的层来说，有限厚度效应是至关重要的，而对于具有刚性尾部的表面活性剂形成的层来说，有限厚度效应的影响不是很明显。事实上，在前一种情况下，与无限薄的表面相比，自发曲率、平均弯曲常数和高斯弯曲常数都发生了显著的变化，并且呈现出相同的值，就好像表面活性剂层以恒定的层厚度弯曲一样。结果表明，自发曲率随膜厚的增加和疏水-亲水界面张力的增加而减小，而弯曲常数的平均值和高斯常数均随厚度的增加而增大。所有这些趋势都与实验观察到的一致。此外，研究还表明，将亲水-疏水界面和电荷表面分开一定的距离，会增加自发曲率和平均弯曲常数，而高斯弯曲常数则变得越来越负。研究还发现，对于具有柔性脂肪链的表面活性剂，将双层膜弯曲成几何封闭的囊泡的功大大增加到较大的正值，而对于具有刚性尾部的表面活性剂，相应的量为负值，这表明只有前者才能形成稳定的双层结构。此外，与相应的单链表面活性剂形成的层相比，由双链离子表面活性剂形成的单层膜的每个弯曲弹性常数都呈现出较低的值。
The bending properties of charged one-component surfactant films of finite thickness have been theoretically investigated. It is demonstrated that finite thickness effects are of crucial importance for layers formed by an ionic surfactant with a flexible hydrophobic tail, whereas the influence on layers formed by a surfactant with a rigid tail is less pronounced. As a matter of fact, in the former case, the spontaneous curvature and mean and Gaussian bending constants all become significantly modified as compared to an infinitely thin surface and assume identical values as if the surfactant layer were bent at constant layer thickness. As a result, the spontaneous curvature is found to decrease, whereas the magnitudes of the mean and Gaussian bending constants both increase with increasing layer thickness as well as with increasing hydrophobic-hydrophilic interfacial tension. All of these trends are consistent with experimental observations. In addition, it is demonstrated that separating the hydrophilic-hydrophobic interface and the surface of charge a certain distance from each other tends to increase the spontaneous curvature and the mean bending constant, whereas the Gaussian bending constant becomes increasingly negative. It is also found that the work of bending a bilayer into a geometrically closed vesicle is substantially raised to large positive values for surfactants with flexible aliphatic chains, whereas the corresponding quantity is negative for surfactants with rigid tails, indicating that stable bilayer structures may only be formed by the former surfactant. Furthermore, each of the bending elasticity constants for monolayers formed by a double-chain ionic surfactant are found to assume lower values as compared with layers formed by the corresponding single-chain surfactant.