Environmentally responsive adsorption and assembly behaviors from N-alkyl-1,2-ethylenediamines
作者:Yi Yang、Jinfeng Dong、Bo Cai、Zan Jiang、Li Cheng、Xuefeng Li
DOI:10.1039/c2sm27288a
日期:——
A series of pH sensitive single-tailed surfactants, N-alkyl-1,2-ethylenediamine (CmN2N, where m = 8, 10, 12, 14, 16), were synthesized and characterized. The adsorption and aggregation properties of them were determined by equilibrium surface tension, static and dynamic light scattering (SLS and DLS), rheology, and cryogenic transmission electron microscopy (cryo-TEM) techniques in detail. It was found that both the surface activity and self-assembly behavior of CmN2N were strongly dependent on the solution pH, owing to the protonation state of amino groups in CmN2N. When at least one of the amino groups of CmN2N was protonated the logarithm of the critical micelle concentration (cmc) followed the well-known Klevens equation, i.e. cmc decreased linearly with the increase of hydrocarbon chain length. Simultaneously, the surface adsorption area per molecule (Amin) was decreased for each CmN2N when the solution pH varied from acidic to basic conditions. The pH-dependent micelle to vesicle transition was universally observed in the bulk phase of CmN2N. More interestingly, the rodlike micelles formed in C10N2N, C12N2N and C14N2N could transform into vesicles reversibly upon heating or cooling, which indicated the thermal sensitivityof organized assemblies, whereas not in C8N2N and C16N2N.
合成并表征了一系列对 pH 值敏感的单尾表面活性剂 N-烷基-1,2-乙二胺(CmN2N,其中 m = 8、10、12、14、16)。通过平衡表面张力、静态和动态光散射(SLS 和 DLS)、流变学和低温透射电子显微镜(cryo-TEM)技术详细测定了它们的吸附和聚集特性。研究发现,由于 CmN2N 中氨基的质子化状态,CmN2N 的表面活性和自组装行为都与溶液的 pH 值密切相关。当 CmN2N 中至少有一个氨基被质子化时,临界胶束浓度(cmc)的对数遵循著名的 Klevens 方程,即 cmc 随烃链长度的增加而线性降低。同时,当溶液的 pH 值从酸性变为碱性时,每种 CmN2N 的每分子表面吸附面积(Amin)都会减小。在 CmN2N 的体相中普遍观察到了与 pH 值相关的胶束到囊泡的转变。更有趣的是,在 C10N2N、C12N2N 和 C14N2N 中形成的棒状胶束在加热或冷却时可逆地转变为囊泡,这表明了有组织组装体的热敏感性,而在 C8N2N 和 C16N2N 中则没有这种现象。