C12(n)-4-C12(n)·2Br头基尺寸对W/O微乳界面组成和结构的影响

合成出具有不同头基尺寸的季铵盐Gemini表面活性剂C12(n)-4-C12(n)·2Br(n=1, 2, 3时分别对应甲基、乙基和丙基, 即四亚甲基-α, ω-二(十二烷基二甲(乙、丙)基溴化铵)). 以稀释法研究C12(n)-4-C12(n)·2Br在庚烷中形成的W/O微乳的组成和结构. 结果表明, 庚烷溶液中的部分己醇参与构成混合界面膜, 从而改善了混合组分的分子几何形状, 生成了稳定的W/O微乳. 随着水含量W0增大, 微乳的水核也随之增大, 变小的界面曲率减小了混合膜对己醇量的需求. 增大C12(n)-4-C12(n)·2Br头基尺寸, 界面层中己醇与表面活性剂的摩尔比(a)先增大(n从1到2)然后再减小(n从2到3). W0愈大, a在n从2到3时减小得愈明显. 在W0=10和20时, 微乳水核半径Rw随n增大而减小; 但在W0=30时, 当n从2到3, Rw反倒明显增大. 这些结果表明, 季铵头基相连的两个丙基其行为与相连两个甲基或两个乙基时不同, 这两个丙基弯曲朝向庚烷, 撑大了表面活性剂烷烃链区域的体积, 致使混合界面膜上己醇分子的需求量减少, 有助于形成较大尺寸的水核.

Effect of the Head-group Size of C12(n)-4-C12(n)·2Br on the Interfacial Composition and Structure of W/O Microemulsion

Butanediyl-α, ω-bis-(dialkyldodecyl-ammonium bromides) (alkyl = methyl, ethyl, and propyl), which referred to as C12(n)-4-C12(n)·2Br (n=1, 2, 3), had been synthesized. The results studied by dilution method showed that a part of n-hexanol in n-heptane together with surfactant constructed a mixed film, which improved the molecular geometry of the mixed components and resulted in the formation of W/O microemulsion. The size of the water pool enlarged with increasing water content W0, which decreased the surface curvature of the water pool and therefore reduced the requirement for n-hexanol in the mixed film. With increasing the head-group size of C12(n)-4-C12(n)·2Br, i.e. n from 1 to 2, the mole ratio of n-hexanol at the film to surfactant a increased, and then decreased with further increasing n from 2 to 3. At W0=10 and 20, the radius of water pool RW reduced with increasing n, but at W0=30, RW increased considerably with increasing n from 2 to 3. These results indicated that the propyl groups linked with quaternary ammonium behaved differently from linked methyl or ethyl groups. The propyl groups may bend toward the bulk n-heptane. This unfurled the volume of the alkyl chain region of surfactant and thus decreased the requirement for n-hexanol in the film, which favored to form large water pool.