CICECO, Departamento de Química, Universidade de Aveiro, 3810-193 Aveiro, Portugal.
Department of Chemical and Process Engineering, University of Strathclyde, 75 Montrose Street, Glasgow G1 1XJ, United Kingdom.
J Phys Chem B. 2020 Aug 13;124(32):7046-7058. doi: 10.1021/acs.jpcb.0c02992. Epub 2020 Aug 4.
The tunable properties of surface-active ionic liquids (SAILs) and Pluronics are dramatically magnified by combining them in aqueous solutions. The thermo-controlled character of both, essential in the extraction of valuable compounds, can be fine-tuned by properly selecting the Pluronic and SAIL nature. However, further understanding of the nanoscale interactions directing the aggregation in these complex mixtures is needed to effectively design and control these systems. In this work, a simple and transferable coarse-grained model for molecular dynamics simulations, based on the MARTINI force field, is presented to study the impact of SAILs in Pluronics aggregation in aqueous solutions. The diverse amphiphilic characteristics and micelle morphologies were exemplified by selecting four archetypical nonionic Pluronics-two normal, L-31 and L-35, and two reverse, 10R5 and 31R1. The impact of the alkyl chain length and the headgroup nature were evaluated with the imidazolium-based [Cmim]Cl and [Cmim]Cl and phosphonium-based [P]Cl SAILs. Cloud point temperature (CPT) measurements at different Pluronic concentrations with 0.3 wt % of SAIL in aqueous solution emphasized the distinct impact of SAIL nature on the thermo-response behavior. The main effect of SAIL addition to nonionic Pluronics aqueous solutions is the formation of Pluronic/SAIL hybrid micelles, where the presence of SAIL molecules introduces a charged character to the micelle surface. Thus, additional energy is necessary to induce micelle aggregation, leading to the observed increase in the experimental CPT curves. The SAIL showed a relatively weak impact in Pluronic micelles with relatively high PPG hydrophobic content, whereas this effect was more evident when the Pluronic hydrophobic/hydrophilic strength is balanced. A detailed analysis of the Pluronic/SAIL micelle density profiles showed that the phosphonium head groups were positioned inside the micelle core, whereas smaller imidazolium head groups were placed much closer to the hydrophilic PEG corona, leading to a distinct effect on the cloud point temperature for those two classes of SAILs. Herein, the phosphonium-based SAIL induces a lower repulsion between neighboring micelles than the imidazolium-based SAILs, resulting in a less pronounced increase of the CPT. The model presented here offers, for the first time, an intuitive and powerful tool to unravel the complex thermo-response behavior of Pluronic and SAIL mixtures and support the design of tailor-made thermal controlled solvents.
表面活性剂离子液体（SAILs）和 Pluronics 的可调性质通过在水溶液中结合它们而大大放大。这两种物质的热控特性在提取有价值的化合物中至关重要，可以通过适当选择 Pluronic 和 SAIL 的性质进行微调。然而，为了有效地设计和控制这些系统，需要进一步了解指导这些复杂混合物中聚集的纳米尺度相互作用。在这项工作中，提出了一种基于 MARTINI 力场的简单且可转移的粗粒化分子动力学模拟模型，用于研究 SAIL 在 Pluronics 聚集在水溶液中的影响。通过选择四种典型的非离子型 Pluronics-两种普通型、L-31 和 L-35，以及两种反相型、10R5 和 31R1，说明了不同的两亲特性和胶束形态。通过咪唑基 [Cmim]Cl 和 [Cmim]Cl 和膦基 [P]Cl SAIL 评估了烷基链长和头基性质的影响。在水溶液中不同 Pluronic 浓度下添加 0.3wt%SAIL 的浊点温度（CPT）测量强调了 SAIL 性质对热响应行为的明显影响。SAIL 对非离子型 Pluronics 水溶液的主要影响是形成 Pluronic/SAIL 混合胶束，其中 SAIL 分子的存在使胶束表面带有电荷。因此，需要额外的能量来诱导胶束聚集，从而导致实验 CPT 曲线的观察到的增加。在具有相对较高 PPG 疏水性含量的 Pluronic 胶束中，SAIL 的影响相对较弱，而当 Pluronic 疏水性/亲水性强度平衡时，这种影响更为明显。对 Pluronic/SAIL 胶束密度分布的详细分析表明，膦基头基位于胶束核心内部，而较小的咪唑基头基更靠近亲水性 PEG 冠，这对这两类 SAIL 的浊点温度产生了明显的影响。在这里，与基于咪唑的 SAIL 相比，基于膦的 SAIL 诱导相邻胶束之间的排斥力更低，导致 CPT 的增加不那么明显。这里提出的模型首次提供了一种直观而强大的工具，可以揭示 Pluronic 和 SAIL 混合物的复杂热响应行为，并支持定制热控溶剂的设计。
