Deo Puspendu, Deo Namita, Somasundaran P, Moscatelli Alberto, Jockusch Steffen, Turro Nicholas J, Ananthapadmanabhan K P, Ottaviani M Francesca
NSF IUCR Center for Advanced Studies in Novel Surfactants, Langmuir Center for Colloid and Interfaces, Columbia University, 3000 Broadway, New York, New York 10027, USA.
Langmuir. 2007 May 22;23(11):5906-13. doi: 10.1021/la063349u. Epub 2007 May 1.
The interaction of a hydrophobically modified anionic polymer (PMAOVE) with a cationic surfactant (DTAB) was studied using a multi-technique approach: turbidity, surface tension, and viscosity measurements, as well as EPR (5-doxyl stearic acid) and fluorescence (pyrene) probe techniques were used. In the investigated pH range (4-10), the cationic surfactant headgroups interact with the anionic carboxylic groups of the polymer backbone. In addition, nonpolar interactions of the surfactant chains with the n-octyl chains of PMAOVE stabilize the PMAOVE-DTAB complexes. Charge neutralization of the anionic polymer by the cationic surfactant leads to precipitation of the PMAOVE-DTAB complex at a certain DTAB concentration range. Further addition of DTAB causes a charge reversal of the complex and, subsequently, resolubilization of the precipitate. At an acidic pH (pH = 4), a second precipitation was observed, which is probably caused by conformational changes in the PMAOVE-DTAB complex. This second precipitate can be resolubilized by further addition of surfactant. At a neutral and basic pH, this second precipitation is absent. EPR analysis indicates that the surfactants form an ordered structure at the extended polymer chain at a neutral and basic pH, whereas at an acidic pH, a less ordered surfactant layer is formed on the coiled polymer with more hydrophobic microdomains.
采用多种技术方法研究了疏水改性阴离子聚合物（PMAOVE）与阳离子表面活性剂（DTAB）之间的相互作用：进行了浊度、表面张力和粘度测量，还使用了电子顺磁共振（EPR，5-硬脂酰氧基苯甲酸）和荧光（芘）探针技术。在所研究的pH范围（4 - 10）内，阳离子表面活性剂的头基与聚合物主链上的阴离子羧基相互作用。此外，表面活性剂链与PMAOVE的正辛基链之间的非极性相互作用使PMAOVE - DTAB复合物得以稳定。阳离子表面活性剂对阴离子聚合物的电荷中和导致PMAOVE - DTAB复合物在一定的DTAB浓度范围内沉淀。进一步添加DTAB会导致复合物电荷反转，随后沉淀重新溶解。在酸性pH（pH = 4）下，观察到第二次沉淀，这可能是由PMAOVE - DTAB复合物的构象变化引起的。通过进一步添加表面活性剂，这种第二次沉淀可以重新溶解。在中性和碱性pH下，不存在这种第二次沉淀。EPR分析表明，在中性和碱性pH下，表面活性剂在伸展的聚合物链上形成有序结构，而在酸性pH下，在具有更多疏水微区的卷曲聚合物上形成的表面活性剂层有序性较低。
