Laboratoire Polymères et Matériaux Avancés, CNRS/Rhodia Recherche et Technologie, 69192 Saint-Fons Cedex, France.
J Phys Chem B. 2010 Mar 25;114(11):3855-62. doi: 10.1021/jp911278j.
A water in oil microemulsion system composed of water, surfactant, and oil, the latter two components of perfluoropolyether (PFPE) type, has been studied by small-angle neutron scattering (SANS) with the aim of knowing the microstructure of the system and to have an insight on the connection between microstructure characterization and percolation behavior. In fact, along the dilution line W/S = 11 of the phase diagram, dielectric spectroscopy and conductivity studies revealed a dynamic percolation process taking place approaching and above the dynamic percolation threshold, leading to a system composed of droplet clusters with percolation thresholds varying with temperature from a 0.501 volume fraction of the dispersed phase at 9.3 degrees C to 0.205 at 32.5 degrees C. The SANS experimental spectra of this work have been studied by modeling the microemulsion droplets as adhesive hard spheres. For all of the samples, the surfactant area per polar head has been also measured in the Porod region of the SANS spectra. Geometric and potential parameters as well as the osmotic pressure, the second virial coefficient, and the distance between droplets have been extracted from data as a function of droplets concentration. At low concentration, that is, below percolation thresholds, the droplets behave as hard spheres, whereas at threshold and above, adhesion changes significantly the samples. In fact, for each temperature, the measured size increases versus concentration from 30 to 50 A, and the area per polar head decreases correspondingly, suggesting that a process of dynamic fusion of droplets occurs in the system above threshold, that is, couples of droplets stick and unstick continuously with interdigitation of the surfactant tails.
由水、表面活性剂和油组成的水包油型微乳液体系，其中后两种成分是全氟聚醚（PFPE）型的，已经通过小角中子散射（SANS）进行了研究，目的是了解体系的微观结构，并深入了解微观结构特征与渗流行为之间的关系。事实上，在相图的 W/S = 11 稀释线上，介电光谱和电导率研究表明，在接近和高于动态渗流阈值的情况下，发生了动态渗流过程，导致系统由具有不同渗流阈值的液滴簇组成，其阈值随温度变化，在 9.3°C 时分散相的体积分数为 0.501，在 32.5°C 时为 0.205。这项工作的 SANS 实验谱已通过将微乳液液滴建模为粘附硬球来研究。对于所有样品，还在 SANS 光谱的 Porod 区域测量了表面活性剂每个极性头的面积。几何和势能参数以及渗透压、第二维里系数和液滴之间的距离已从数据中作为液滴浓度的函数提取出来。在低浓度，即低于渗流阈值时，液滴表现为硬球，而在阈值及以上时，粘附显著改变了样品。事实上，对于每个温度，测量的尺寸从 30 到 50 A 随浓度增加，而每个极性头的面积相应减小，这表明在系统高于阈值时发生了液滴的动态融合过程，即液滴对不断地相互粘附和脱离，同时表面活性剂尾部相互穿插。
