Department of Chemical Engineering, University of Michigan , 2800 Plymouth Road, Ann Arbor, Michigan 48109, United States.
Modeling and Simulation, The Procter & Gamble Company , 8611 Beckett Road, West Chester, Ohio 45069, United States.
J Phys Chem B. 2017 Mar 23;121(11):2468-2485. doi: 10.1021/acs.jpcb.7b00257. Epub 2017 Mar 13.
We link micellar structures to their rheological properties for two surfactant body-wash formulations at various concentrations of salts and perfume raw materials (PRMs) using molecular simulations and micellar-scale modeling, as well as traditional surfactant packing arguments. The two body washes, namely, BW-1EO and BW-3EO, are composed of sodium lauryl ethylene glycol ether sulfate (SLEnS, where n is the average number of ethylene glycol repeat units), cocamidopropyl betaine (CAPB), ACCORD (which is a mixture of six PRMs), and NaCl salt. BW-3EO is an SLE3S-based body wash, whereas BW-1EO is an SLE1S-based body wash. Additional PRMs are also added into the body washes. The effects of temperature, salt, and added PRMs on micellar lengths, breakage times, end-cap free energies, and other properties are obtained from fits of the rheological data to predictions of the "Pointer Algorithm" [ Zou , W. ; Larson , R.G. J. Rheol. 2014 , 58 , 1 - 41 ], which is a simulation method based on the Cates model of micellar dynamics. Changes in these micellar properties are interpreted using the Israelachvili surfactant packing argument. From coarse-grained molecular simulations, we infer how salt modifies the micellar properties by changing the packing between the surfactant head groups, with the micellar radius remaining nearly constant. PRMs do so by partitioning to different locations within the micelles according to their octanol/water partition coefficient P and chemical structures, adjusting the packing of the head and/or tail groups, and by changing the micelle radius, in the case of a large hydrophobic PRM. We find that relatively hydrophilic PRMs with log P < 2 partition primarily to the head group region and shrink micellar length, decreasing viscosity substantially, whereas more hydrophobic PRMs, with log P between 2 and 4, mix with the hydrophobic surfactant tails within the micellar core and slightly enhance the viscosity and micelle length, which is consistent with the packing argument. Large and very hydrophobic PRMs, with log P > 4, are isolated deep inside the micelle, separating from the tails and swelling the radius of the micelle, leading to shorter micelles and much lower viscosities, leading eventually to swollen-droplet micelles.
我们使用分子模拟和胶束尺度建模以及传统的表面活性剂组装参数，将胶束结构与其流变性质联系起来，研究了两种不同盐浓度和香料原料 (PRMs) 浓度下的两种沐浴露配方，这两种沐浴露分别是 BW-1EO 和 BW-3EO，它们由月桂基聚氧乙烯醚硫酸钠盐（SLEnS，其中 n 是乙二氧基重复单元的平均数量）、椰油酰胺丙基甜菜碱 (CAPB)、混合物 ACCORD（由六种 PRMs 组成）和 NaCl 盐组成。BW-3EO 是基于 SLE3S 的沐浴露，而 BW-1EO 是基于 SLE1S 的沐浴露。此外，还向沐浴露中添加了其他 PRMs。从流变数据拟合到“Pointer Algorithm”[Zou, W. ; Larson, R.G. J. Rheol. 2014, 58, 1 - 41]的预测中，得到了温度、盐和添加的 PRMs 对胶束长度、断裂时间、端帽自由能和其他性质的影响，该算法是一种基于胶束动力学的 Cates 模型的模拟方法。使用 Israelachvili 表面活性剂组装参数来解释这些胶束性质的变化。从粗粒分子模拟中，我们推断盐如何通过改变表面活性剂头基之间的组装来改变胶束性质，而胶束半径保持几乎不变。根据它们的辛醇/水分配系数 P 和化学结构，PRMs 可以在不同的位置分配到胶束内，从而调整头基和/或尾基的组装，并通过改变大疏水性 PRM 的胶束半径，来调整胶束性质。我们发现，具有 logP < 2 的相对亲水性 PRMs 主要分配到头基区域，从而缩短胶束长度，显著降低粘度，而 logP 在 2 到 4 之间的疏水性 PRMs 与胶束核心内的疏水性表面活性剂尾基混合，略微增加粘度和胶束长度，这与组装参数一致。具有 logP > 4 的大疏水性 PRMs 被隔离在胶束内部深处，与尾部分离并使胶束半径膨胀，导致胶束变短，粘度大大降低，最终导致肿胀的液滴胶束。
