Stranski Laboratorium für Physikalische und Theoretische Chemie, Technische Universität Berlin, Strasse des 17. Juni 124, D-10623 Berlin, Germany.
J Phys Chem B. 2010 Apr 1;114(12):4183-91. doi: 10.1021/jp911400j.
The surface aggregate structure of dimethyldodecylamine-N-oxide (C(12)DAO) in three silica dispersions of different particle sizes (16-42 nm) was studied by small-angle neutron scattering (SANS) in a H(2)O/D(2)O solvent mixture matching the silica. At the experimental conditions (pH 9), the surfactant exists in its nonionic form, and the structure of the adsorbed layer is not affected by added electrolyte. It is found that C(12)DAO forms spherical surface micelles of 2 nm diameter on the 16 nm silica particles, but oblate ellipsoidal surface micelles are formed on the 27 and 42 nm particles. The dimensions of these oblate surface aggregates (minor and major semiaxes R(n) and R(lat)) are similar to those of C(12)DAO micelles in the aqueous solutions. It is concluded that the morphological transition from spherical to ellipsoidal surface aggregates is induced by the surface curvature of the silica particles. A comparison of the shape and dimensions of the surface aggregates formed by C(12)DAO and C(12)E(5) on the 16 nm silica particles demonstrates that the nature of the surfactant head group does not determine the morphology of the surface aggregates but has a strong influence on the number of surface aggregates per particle due to the different interactions of the head groups with the silica surface.
用小角中子散射（SANS）研究了不同粒径（16-42nm）的三种二氧化硅分散体中，二甲基十二烷基氧化胺（C(12)DAO）的表面聚集体结构。在实验条件下（pH9），表面活性剂以非离子形式存在，吸附层的结构不受外加电解质的影响。结果发现，C(12)DAO 在 16nm 的二氧化硅颗粒上形成了 2nm 直径的球形表面胶束，但在 27nm 和 42nm 的颗粒上形成了扁长椭球形表面胶束。这些扁长的表面聚集体的尺寸（小轴和大轴 R(n)和 R(lat))与水溶液中 C(12)DAO 胶束的尺寸相似。由此推断，球形到椭球形表面聚集体的形态转变是由二氧化硅颗粒的表面曲率引起的。比较 C(12)DAO 和 C(12)E(5)在 16nm 二氧化硅颗粒上形成的表面聚集体的形状和尺寸表明，表面活性剂头基的性质并不决定表面聚集体的形态，而是由于头基与二氧化硅表面的不同相互作用，对每个颗粒上的表面聚集体数量有很强的影响。
