Poly(ethylenimine) as a subphase stabilizer of stearic acid monolayers at the air water interface: Surface pressure-area isotherm and infrared spectroscopy study

被引:38
作者
Hwang, MJ
Kim, K [1 ]
机构
[1] Seoul Natl Univ, Dept Chem, Seoul 151742, South Korea
[2] Seoul Natl Univ, Ctr Mol Catalysis, Seoul 151742, South Korea
关键词
D O I
10.1021/la9804029
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
The effect of poly(ethylenimine) (PEI) dissolved in water on the surface pressure-area (pi-A) isotherm of stearic acid (STA) at the air/water interface was investigated. When the concentration of PEI was quite low, for example, 2.2 x 10(-4) g/L (5.1 x 10(-6) M in monomeric unit concentration), the isotherm of the STA monolayer was little affected by PEI. On a concentrated PEI solution, for example, at 2.2 x 10(-2) g/L, the isotherm of the STA monolayer exhibited a noticeable variation as a function of subphase pH; particularly in basic conditions. The isotherm of STA could be obtained very reproducibly even at pH 10.4. At basic pHs, PEI induced the occurrence of a wide plateau region in an isotherm that could be attributed to the coexistence of liquid-condensed (LC) and liquid-expanded (LE) phases of STA on a water subphase. In addition, the collapse pressure of the STA monolayer was raised to 68 mN/m, indicating that the stability of the monolayer could be increased dramatically by virtue of an acid-base-type interaction between the amine group of PEI and the carboxyl group of STA. In situ reflection-absorption infrared (RAIR) spectroscopy revealed that at acidic pi-Is STA molecules should form two-dimensional crystalline domains even at high "per molecular" area. In contrast, at basic pHs RAIR spectral data dictated that STA molecules were strongly disordered at high per molecular area, and a near-crystalline structure seemed to form only when the per molecular area was lowered to a value corresponding to a pure LC phase in the pi-A isotherm of STA on the PEI-containing subphase.
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页码:3563 / 3569
页数:7
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