Polarization modulation infrared reflection absorption spectroscopy of Gibbs monolayer at the air/water interface
Polarization modulation infrared reflection absorption spectroscopy of Gibbs monolayer at the air/water interface
复制标题
空气/水界面吉布斯单分子层的偏振调制红外反射吸收光谱
作者：
M. Islam;and Yanzhi Ren;Teiji Kato
采用偏振调制红外反射吸收光谱（PM-IRRAS）研究了乙二醇单正十二烷基醚（EGDE）在空气-水界面上的自发吸附.布鲁斯特角显微图像显示，EGDE单层形成的凝聚态的圆形域。PM-IRRAS测量结果显示，在2918.2cm- 1处有一个ν as（CH 2）带，在1469.2cm- 1处有一个δ（CH 2）带，分别表明-（CH 2）11-链的平面反式锯齿构象和结晶堆积.ν as（C-O-C）模式给出了一个负带，表明醚键优先在Gibbs单分子层中起作用。利用传统的Langmuir-Blodgett技术成功地将Gibbs单分子膜转移到固体基底上，如Au和CaF 2。红外透射和反射测量的转移单分子膜，以获得各向异性的复折射率。使用这些指标，PM-IRRAS光谱的EGDE单分子膜在空气/亚相界面的模拟和实验进行了比较。结果表明，-（CH 2）11-链在水相中相对于表面法线倾斜21°，扭转56°. LB转移到固体基质上的物理作用引起了-（CH 2）1 1 -链和醚键的重新取向以及链构象顺序的劣化。
Polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) was applied to investigate Gibbs monolayers of ethylene glycol mono-n-dodecyl ether (EGDE), spontaneously adsorbed at the interface of air andaqueous EGDE subphase. Brewster angle microscopic images reveal that the EGDE monolayer forms circular domains in a condensed state. The PM-IRRAS measurements reveal a ν a s (CH 2 ) band at 2918.2 cm - 1 and a δ(CH 2 ) band at 1469.2 cm - 1 , indicating respectively the planar trans zigzag conformation and crystalline packing of the -(CH 2 ) 1 1 - chain. The ν a s (C-O-C) mode gives a negative band, implying that the ether linkage preferentially stands up in the Gibbs monolayer. The Gibbs monolayer was successfully transferred onto solid substrates such as Au and CaF 2 , using the conventional Langmuir-Blodgett technique. Infrared transmission and reflection measurements of the transferred monolayer were applied to obtain the anisotropic complex refractive indexes. Using these indexes, the PM-IRRAS spectrum of the EGDE monolayer at the air/subphase interface was simulated and compared to the experimental one. It is concluded that the -(CH 2 ) 1 1 - chain is tilted at 21° with respect to the surface normal and twisted at 56° on the aqueous subphase. The physical act of LB transfer onto solid substrates has caused reorientation of the -(CH 2 ) 1 1 - chain and the ether linkage as well as deterioration of the chain conformational order.