Lundberg Dan, Unga Johan, Galloway Ashley L, Menger Fredric M
Department of Chemistry, Emory University, Atlanta, Georgia 30322, USA.
Langmuir. 2007 Nov 6;23(23):11434-42. doi: 10.1021/la700430u. Epub 2007 Oct 9.
The aqueous behavior of an ester-modified cationic amphiphile with the molecular structure CH3CH2O(C=O)(CH2)6(C=O)O(CH2)8N+(CH3)3Br-, in the following referred to as A, has been investigated. Systems with A as the only solute, as well as different aqueous mixtures with conventional cationic surfactants, primarily dodecyltrimethylammonium bromide (DTAB), were included in the study. Isotropic solution samples were characterized using 1H NMR, 13C NMR, NMR diffusometry, and conductivity measurements, whereas liquid crystalline samples were investigated by optical polarization microscopy and small-angle X-ray diffraction. The results are compared to the behavior of the binary system of DTAB and water. A does not exhibit a typical surfactant behavior. When it is present as the only solute in a binary aqueous system, it forms neither conventional micelles nor liquid crystalline phases. However, there is clear evidence that it assembles with lower cooperativity into loose clusters at concentrations above 25-30 mM. When A is mixed with DTAB in solution, the two amphiphiles form mixed assemblies, the structure of which varies with the total amphiphile concentration. In concentrated mixtures with alkyltrimethylammonium surfactants, A can participate in hexagonal liquid crystalline phases even when it constitutes a significant fraction of the total amphiphile content.
对一种分子结构为CH3CH2O(C=O)(CH2)6(C=O)O(CH2)8N+(CH3)3Br-(以下简称A)的酯改性阳离子两亲物的水相行为进行了研究。该研究包括以A为唯一溶质的体系,以及与传统阳离子表面活性剂(主要是十二烷基三甲基溴化铵,DTAB)形成的不同水相混合物。各向同性溶液样品通过1H NMR、13C NMR、NMR扩散法和电导率测量进行表征,而液晶样品则通过光学偏振显微镜和小角X射线衍射进行研究。将结果与DTAB和水的二元体系的行为进行比较。A不表现出典型的表面活性剂行为。当它作为二元水体系中的唯一溶质存在时,既不形成传统的胶束也不形成液晶相。然而,有明确证据表明,在浓度高于25 - 30 mM时,它会以较低的协同性聚集形成松散的聚集体。当A与DTAB在溶液中混合时,这两种两亲物会形成混合聚集体,其结构随总两亲物浓度而变化。在与烷基三甲基铵表面活性剂的浓混合物中,即使A占总两亲物含量的很大一部分,它也能参与形成六方液晶相。