Temperature-dependent aggregation behavior of symmetric long-chain bolaamphiphiles at the air-water interface.
Temperature-dependent aggregation behavior of symmetric long-chain bolaamphiphiles at the air-water interface.
复制标题
对称长链双亲分子在空气-水界面的温度依赖性聚集行为。
作者：
K. Köhler;A. Meister;B. Dobner;Simon Drescher;F. Ziethe;A. Blume
采用变温膜天平和布鲁斯特角显微镜研究了对称长链bola两亲分子双[2-（二甲氨基）乙基]磷酸三十二烷-1，32-二酯（PC-C32-PC）和双[2-（二甲氨基）乙基]磷酸三十二烷-1，32-二酯（Me（2）PE-C32-Me（2）PE）在空气-水界面上的行为.压缩后的单层的等温线显示出强烈的表面压力增加。我们假设，在高压下的单分子层由一个倒U形构象的分子。在每个分子0.9-1.1 nm（2）的面积处，两种bola两亲物都达到了平台期，这标志着水面上聚集体形成的开始。平台压力随温度升高而升高。对于PC-C32-PC，在6.7 ℃下，在水面上观察到直径为20-30 μ m的弯曲较短纤维域，而在29.2 ℃下观察到厚度为200-500 μ m的条状域。在此温度范围内记录的等温线显示了陡坡内的特征性断裂，标志着两种结构的混合物或混合形式存在的区域。Me（2）PE-C32-Me（2）PE在低pH下以其两性离子状态在水表面上形成微晶，其形成在动力学上被延迟。取决于温度，含水亚相或多或少均匀地覆盖有晶体状膜。相反，当bola两亲物带负电荷时，在pH 10下没有观察到聚集体。
The behavior of the symmetric long-chain bolaamphiphiles dotriacontane-1,32-diyl bis[2-(trimethylammonio)ethyl phosphate] (PC-C32-PC), and dotriacontane-1,32-diyl bis[2-(dimethylammonio)ethyl phosphate] (Me(2)PE-C32-Me(2)PE) at the air-water interface was investigated by means of temperature-dependent film-balance measurements and Brewster angle microscopy. Upon compression of the monolayer the isotherms show a strong surface pressure increase. We assume that at high pressure the monolayer consists of molecules in a reversed U-shaped conformation. At an area of 0.9-1.1 nm(2) per molecule a plateau is reached for both bolaamphiphiles, which marks the beginning of an aggregate formation on the water surface. The plateau pressure increases with increasing temperature. For PC-C32-PC at 6.7 degrees C curved shorter fibrous domains with a diameter of 20-30 mum are seen on the water surface, whereas at 29.2 degrees C stripelike domains with a thickness of 200-500 mum are observed. Isotherms recorded within this temperature range show a characteristic break within the steep slope marking a region where a mixture or a hybrid form of both structures exists. Me(2)PE-C32-Me(2)PE in its zwitterionic state at low pH forms microcrystals on the water surface, whose formation is kinetically retarded. Depending on the temperature, the aqueous subphase is more or less homogeneously covered with a crystalline-like film. In contrast, no aggregates are observed at pH 10 when the bolaamphiphile is negatively charged.