Study of the coadsorption of an anionic surfactant and an uncharged polymer at the aqueous solution/hydrophobic surface interface by sum frequency spectroscopy
Study of the coadsorption of an anionic surfactant and an uncharged polymer at the aqueous solution/hydrophobic surface interface by sum frequency spectroscopy
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DOI：
10.1021/la030106i
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发表时间：
2003-09-02
期刊：
影响因子：
3.9
通讯作者：
Neivandt, DJ
中科院分区：
文献类型：
--
作者：
Casford, MTL;Davies, PB;Neivandt, DJ
研究了在存在和不存在固定浓度的聚环氧乙烷 (PEO) 的情况下，吸附在疏水性十八烷硫醇/水溶液界面上的十二烷基硫酸钠 (SDS) 的极性取向和构象有序度与表面活性剂浓度的函数关系。利用和频振动光谱法，基于和频产生的非线性光学现象，获得了界面活性剂的光谱；还获得了界面处 PEO 的微弱信号。光谱的相表明表面活性剂和聚合物均具有朝向疏水表面的CH 2 和/或CH 3 基团的净取向。混合聚合物/表面活性剂溶液存在下的 SDS 光谱显示，随着表面活性剂浓度的增加，构象有序性增加。在最低表面活性剂浓度下，存在聚合物时的 SDS 光谱比不存在聚合物时的光谱弱。通过使用全氘化 SDS 专门探测界面 PEO 表明，当表面活性剂浓度增加到阈值浓度以上时，聚合物光谱强度降低。这些发现是根据低 SDS 浓度下的竞争性聚合物/表面活性剂吸附来解释的。在存在和不存在添加电解质的情况下，当表面活性剂浓度接近临界聚集浓度时，归因于聚合物的和频信号消失。这一发现可能归因于持续的 PEO 解吸、表面结合 SDS/PEO 复合物的形成或这两个过程的组合。
The polar orientation and degree of conformational order of sodium dodecyl sulfate (SDS) adsorbed at the hydrophobic octadecane thiol/aqueous solution interface has been investigated as a function of the surfactant concentration in the presence and absence of a fixed concentration of poly(ethylene oxide) (PEO). Sum frequency vibrational spectroscopy, based on the nonlinear optical phenomenon of sum frequency generation, was employed to obtain spectra of the interfacial surfactant; weak signals from PEO at the interface were also obtained. The phase of the spectra indicated that both the surfactant and the polymer had a net orientation of their CH2 and/or CH3 groups toward the hydrophobic surface. Spectra of SDS in the presence of mixed polymer/surfactant solutions showed increasing conformational order as the surfactant concentration was raised. At the lowest surfactant concentration, the spectra of SDS were weaker in the presence of the polymer than in its absence. Probing interfacial PEO specifically through the use of perdeuterated SDS revealed that the polymer spectral intensity decreased as the surfactant concentration was increased above a threshold concentration. These findings are interpreted in terms of competitive polymer/surfactant adsorption at low SDS concentrations. In both the presence and the absence of added electrolyte, the sum frequency signal attributable to the polymer disappeared as the surfactant concentration approached the critical aggregation concentration. This finding may potentially be attributed to continued PEO desorption, to the formation of surface-bound SDS/PEO complexes, or to a combination of the two processes.