摘要
本文总结了Gemini表面活性剂分子结构中联接链在其自组织过程中所发挥的独特作用,这主要来自联接链长度和刚柔性两方面的效应,这些效应综合导致了Gemini分子两条烷烃尾链的协同作用、头基电荷密度改变、分子几何变化以及由此决定的多样化聚集体结构及形貌等。更具体地讲,柔性联接链主要依赖不同长度影响分子的上述功能。过长的联接链还可能通过自身弯曲来适应环境,从而影响分子自组织。短刚性联接链的效应等同于类似长度的柔性联接链,而长刚性联接链由于阻碍了两条烷烃尾链的靠拢,产生了两个突出特征:分子呈似柱形状以及同等几率的两条尾链沿联接链顺式或反式排列构型。这使得长刚性联接链分子在低浓度时就可形成网状聚集体,增加浓度或少量添加剂干扰易转变成低表面曲率的线状胶束或囊泡。适合条件还可催生少量反式构型分子,它们将一条烷烃尾链伸出聚集体外,通过疏水相互作用串接相邻的聚集体。本文也讨论了对联接链进行的化学修饰,这有望促进分子的自组织活性,或者赋予聚集体某种新的特殊功能。列举的例子很好表明了Gemini分子结构的独特性,以及Gemini表面活性剂复杂的自组织行为和多样化的聚集结构。
The special and unique role of the spacer of Gemini surfactant in self-assembly is reviewed, which is considered to benefit mainly from both the spacer length and the rigid/flexible features. These two effects lead to the synergism of two alkyl tails of a Gemini molecule, the change in the charge density of its headgroups, the variation of its molecule geometry by which rich structures and morphologies of aggregates yield, etc. More detailed, the flexible spacer influences the above functions of the Gemini mainly depending on its length. Too long flexible spacer can bend toward the alkyl tails so as to meet the chemical environment around the molecule, by which the molecule self-assembly is influenced. The effect of the short rigid spacer is almost identical with that of the flexible spacer having a similar length. However, the long rigid spacer yields quite different effects from the flexible spacer owing to the two alkyl tails are inhibited to be close, which leads to the column-like molecular shape and the identical probability for the cis/trans configuration of the two alkyl tails around the spacer. These make the Geminis with long rigid spacer form network-like aggregates at low concentrations, which can be transformed into threadlike micelles or vesicles with low surface curvature with increasing the Gemini concentration or adding a few additives. Under suitable conditions, a few molecules in the aggregates can be hastened to yield trans-form, resultingin the cohesion between the aggregates through the hydrophobic interactions between the extended alkyl tails. The chemical modification for the spacer is also discussed, which is expected to promote molecular self-assembly, or give some new functions to the aggregates. The cases listed here well indicate the specialty and uniqueness of the Gemini-structure of molecule and impress us for the complicated self-assembly behavior and diversified aggregates of Gemini surfactants.
出处
《化学进展》
SCIE
CAS
CSCD
北大核心
2014年第8期1339-1351,共13页
Progress in Chemistry
