Department of Chemistry, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215, USA.
J Chem Phys. 2018 Oct 14;149(14):144901. doi: 10.1063/1.5042771.
Reverse micelles (RMs) are recognized as a paradigm of molecular self-assembly and used in a variety of applications, such as chemical synthesis and molecular structure refinement. Nevertheless, many fundamental properties including their equilibrium size distribution, internal structure, and mechanism of self-assembly remain poorly understood. To provide an enhanced microscopic understanding of the assembly process and resulting structural distribution, we perform multiple nonequilibrium molecular dynamics simulations of dioctyl sulfosuccinate sodium salt (AOT) RM assembly, quantifying RM size, water core structure, and dynamics. Rapid assembly of smaller RM from a random mixture is observed to establish a constant AOT water loading within a nanosecond consistent with a diffusion-adsorption mechanism validated through the Monte-Carlo simulation of a model system. The structure of RM water cores and RM molecular volume during RM assembly is characterized during the AOT assembly process. A moment-closure equation is developed from a novel master equation model to elucidate the elementary events underlying the AOT self-assembly process. The resulting kinetic model is used to explore the role of monomer addition and dissociation, RM association and dissociation, and RM collision-induced exchange, all dependent on average RM size, which provides fundamental insight regarding the mechanisms and time scales for AOT RM self-assembly. The nascent dynamics that rapidly establish water loading, intermediate time scales of RM fusion, and longer time scale dynamics of inter-RM exchange essential in establishing the equilibrium condition are quantified through these kinetic models. Overall, this work provides insight into AOT RM self-assembly and provides a general theoretical framework for the analysis of the molecular self-assembly dynamics and mechanism.
反胶束（RMs）被认为是分子自组装的范例，并在各种应用中得到了广泛应用，如化学合成和分子结构精修。然而，许多基本性质，包括它们的平衡尺寸分布、内部结构和自组装机制，仍然知之甚少。为了提供对组装过程和由此产生的结构分布的增强微观理解，我们对二辛基琥珀酸磺酸钠（AOT）RM 组装进行了多次非平衡分子动力学模拟，定量研究了 RM 的大小、水核结构和动力学。我们观察到较小的 RM 从随机混合物中快速组装，在纳秒内建立了恒定的 AOT 水负载，这与通过模型系统的 Monte-Carlo 模拟验证的扩散吸附机制一致。在 AOT 组装过程中，研究了 RM 水核和 RM 分子体积的结构。从一个新的主方程模型中开发了一个矩闭合方程，以阐明 AOT 自组装过程的基本事件。所得的动力学模型用于研究单体的添加和解离、RM 的缔合和解离以及 RM 碰撞诱导交换的作用，所有这些都取决于平均 RM 大小，这为 AOT RM 自组装的机制和时间尺度提供了基本的见解。通过这些动力学模型，定量研究了快速建立水负载的初生动力学、RM 融合的中间时间尺度以及建立平衡条件所必需的 RM 间交换的较长时间尺度动力学。总的来说，这项工作深入了解了 AOT RM 的自组装，并为分析分子自组装动力学和机制提供了一个通用的理论框架。
