Chemistry Department, University of Coimbra, Coimbra 3004-535, Portugal.
Langmuir. 2013 Aug 13;29(32):10047-58. doi: 10.1021/la401871x. Epub 2013 Jul 31.
The amphiphilic properties of conjugated oligoelectrolytes (COE) and their sensitivity to the polarity of their microenvironment lead to interesting aggregation behavior, in particular in their interaction with surfactants. Photoluminescence (PL) spectroscopy, liquid-phase atomic force microscopy, small-angle neutron scattering, small-angle X-ray scattering, and grazing-incidence X-ray diffraction were used to examine interactions between cationic p-phenylene vinylene based oligoelectrolytes and surfactants. These techniques indicate the formation of COE/surfactant aggregates in aqueous solution, and changes in the photophysical properties are observed when compared to pure aqueous solutions. We evaluate the effect of the charge of the surfactant polar headgroup, the size of the hydrophobic chain, and the role of counterions. At low COE concentrations (micromolar), it was found that these COEs display larger emission quantum efficiencies upon incorporation into micelles, along with marked blue-shifts of the PL spectra. This effect is most pronounced in the series of anionic surfactants, and the degree of blue shifts as a function of surfactant charge is as follows: cationic < nonionic < anionic surfactants. In anionic surfactants, such as sodium dodecyl sulfate (SDS), the PL spectra show vibronic resolution above the critical micelle concentration of the surfactant, suggesting more rigid structures. Scattering data indicate that in aqueous solutions, trimers appear as essentially 3-dimensional particles, while tetra- and pentamers form larger, cylindrical particles. When the molar ratio of nonionic C12E5 surfactant to 1,4-bis(4-{N,N-bis-[(N,N,N-trimethylammonium)hexyl]amino}-styryl)benzene tetraiodide (DSBNI) is close to one, the size of the formed DSBNI-C12E5 particles corresponds to the full coverage of individual oligomers. When these particles are transferred into thin films, they organize into a cubic in-plane pattern. If anionic SDS is added, the formed DSBNI-SDS particles are larger than expected for full surfactant coverage, and particles may thus contain several oligomers. This tendency is attributed to the merging of DSBNI oligomers due to the charge screening and, thus, reduced water solubility.
共轭寡电解质（COE）的两亲性质及其对微环境极性的敏感性导致了有趣的聚集行为，特别是在与表面活性剂的相互作用中。荧光（PL）光谱、液相原子力显微镜、小角中子散射、小角 X 射线散射和掠入射 X 射线衍射被用于研究阳离子型苯并二噻吩寡电解质与表面活性剂之间的相互作用。这些技术表明在水溶液中形成了 COE/表面活性剂聚集体，并且与纯水溶液相比观察到光物理性质的变化。我们评估了表面活性剂极性头基团的电荷、疏水性链的大小以及反离子的作用的影响。在低 COE 浓度（微摩尔）下，发现这些 COE 在掺入胶束时显示出更大的发射量子效率，同时 PL 光谱发生明显的蓝移。这种效应在阴离子表面活性剂系列中最为明显，并且 PL 光谱的蓝移程度随表面活性剂电荷的变化如下：阳离子<非离子<阴离子表面活性剂。在阴离子表面活性剂（如十二烷基硫酸钠（SDS））中，PL 光谱在表面活性剂的临界胶束浓度之上显示出振动态分辨率，表明结构更刚性。散射数据表明，在水溶液中，三聚体主要呈现为三维粒子，而四聚体和五聚体形成较大的、圆柱形的粒子。当非离子 C12E5 表面活性剂与 1,4-双（4-｛N,N-双-[(N,N,N-三甲基铵)己基]氨基ｰ苯乙烯基｝苯四碘化物（DSBNI）的摩尔比接近 1 时，形成的 DSBNI-C12E5 粒子的大小对应于单个低聚物的完全覆盖。当这些粒子被转移到薄膜中时，它们会形成一个平面内的立方图案。如果加入阴离子 SDS，则形成的 DSBNI-SDS 粒子比完全覆盖表面活性剂所需的尺寸大，因此粒子可能包含几个低聚物。这种趋势归因于 DSBNI 低聚物由于电荷屏蔽而合并，从而降低了水的溶解度。
