Effect of electrolytes on the surface behavior of rhamnolipids R1 and R2
Effect of electrolytes on the surface behavior of rhamnolipids R1 and R2
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DOI：
10.1016/j.colsurfb.2004.01.001
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发表时间：
2004-06-01
影响因子：
5.8
通讯作者：
Özdemir, G
中科院分区：
文献类型：
--
作者：
Helvaci, SS;Peker, S;Özdemir, G
通过表面张力测量和光学显微镜在pH 6.8条件下研究了鼠李糖脂溶液R1和R2在无电解质(NaC L)和有电解质(NaC L)存在下的表面行为。所研究的氯化钠浓度分别为0.05、0.5和1M。电解质直接影响大黄磷脂的羧酸基。在pH为6.8时，由于解离的羧酸根离子与鼠李糖脂分子之间存在很强的排斥力，溶液/空气界面具有净负电荷。在氯化钠存在的情况下，这种负电荷被双电层中的Na+离子屏蔽，导致形成紧密堆积的单分子膜，CMC和表面张力值下降。对于R1和R2单分子膜，在0.5M的氯化钠浓度下观察到最大的致密化，且R1单层比R2更致密。由于缺少第二鼠李糖基团，R1疏水尾巴下方相对于R2留下了更大的空间，这被认为是导致较高压实度的原因。随着电解液浓度的增加，R1和R2单分子膜的硬度都增加。由于R1具有较低的亲水性，因此在所有的NaC l浓度下，R1单分子膜的刚性都大于R2。由表面张力测量和临界堆积参数(CPP)计算得到的cmC值随氯化钠浓度的变化表明，鼠李糖脂溶液中形成了球形胶束、双层胶束和棒状胶束。光学显微镜的结果支持这些聚集态，表明在R1和R2溶液中，层状向列相、立方层状和六方相液晶相取决于氯化钠浓度。(C)2004爱思唯尔B.V.保留所有权利。
The surface behavior of solutions of the rhamnolipids, R1 and R2, were investigated in the absence and presence of an electrolyte (NaCl) through surface tension measurements and optical microscopy at pH 6.8. The NaCl concentrations studied are 0.05, 0.5 and 1 M. Electrolytes directly affect the carboxylate groups of the rharmolipids. The solution/air interface has a net negative charge due to the dissociated carboxylate ions at pH 6.8 with strong repulsive electrostatic forces between the rhamnolipid molecules. This negative charge is shielded by the Na+ ions in the electrical double layer in the presence of NaCl, causing the formation of a close-packed monolayer, and a decrease in CMC, and surface tension values. The maximum compaction is observed at 0.5 M NaCl concentrations for R1 and R2 monolayers, with the R1 monolayer more compact than R2. The larger spaces left below the hydrophobic tails of R1 with respect to that of R2, due to the missing second rhamnosyl groups are thought to be responsible for the higher compaction. The rigidity of both R1 and R2 monolayers increases with the electrolyte concentration. The rigidity of the R1 monolayer is greater than that of R2 at all NaCl concentrations due to the lower hydrophilic character of R1. The variation of CMC values as a function of NaCl concentration obtained from the surface tension measurements and critical packing parameter (CPP) calculations show that spherical micelles, bilayer and rod like micelles are formed in the rhamnolipid solutions as a function of the NaCl concentration. The results of optical microscopy supported these aggregation states indicating lamellar nematic liquid crystal, Cubic lamellar and hexagonal liquid crystal phases in R1 and R2 solutions depending on the NaCl concentration. (C) 2004 Elsevier B.V. All rights reserved.