Appell Jacqueline, Porte Grégoire, Buhler Eric
Laboratoire des Colloides, Verres, Nanomateriaux (LCVN), UMR5587 CNRS-Université Montpellier IIC.C.26, F-34095 Montpellier Cedex 05, France.
J Phys Chem B. 2005 Jul 14;109(27):13186-94. doi: 10.1021/jp051016k.
A microemulsion of decane droplets stabilized by a nonionic surfactant film is progressively charged by substitution of a nonionic surfactant molecule by a cationic surfactant. We check that the microemulsion droplets remain identical within the explored range of volume fraction (0.02-0.18) and of the number of charges per droplet (0-40). We probe the dynamics of these microemulsions by dynamic light scattering. Despite the similar structures of the uncharged and charged microemulsions, the dynamics are very different. In the neutral microemulsion, the fluctuations of polarization relax, as is well-known, via the collective diffusion of the droplets. In the charged microemulsions, two modes of relaxation are observed. The fast one is ascribed classically to the collective diffusion of the charged droplets coupled to the diffusion of the counterions. The slow one has, to our knowledge, not been observed previously neither in similar microemulsions nor in charged spherical colloids. We show that the slow mode is also diffusive and suggest that its possible origin is the relaxation of local charge fluctuations via the local exchange of droplets bearing different numbers of charges. The diffusion coefficient associated with this mode is then the self-diffusion coefficient of the droplets.
由非离子表面活性剂膜稳定的癸烷微乳液，通过用阳离子表面活性剂取代非离子表面活性剂分子而逐渐带电。我们验证了在探索的体积分数范围（0.02 - 0.18）和每个微乳液滴的电荷数范围（0 - 40）内，微乳液滴保持不变。我们通过动态光散射探测这些微乳液的动力学。尽管不带电和带电微乳液的结构相似，但动力学却非常不同。在中性微乳液中，极化涨落通过液滴的集体扩散而弛豫，这是众所周知的。在带电微乳液中，观察到两种弛豫模式。快速模式传统上归因于带电液滴的集体扩散与抗衡离子扩散的耦合。据我们所知，慢速模式在类似的微乳液或带电球形胶体中都未曾观察到。我们表明慢速模式也是扩散性的，并提出其可能的起源是通过携带不同电荷数的液滴的局部交换来弛豫局部电荷涨落。与该模式相关的扩散系数就是液滴的自扩散系数。
