Department of Chemistry, Sardar Vallabhbhai National Institute of Technology (SVNIT), Ichchhanath, Surat, Gujarat 395 007, India.
CICECO─Aveiro Institute of Materials, Department of Chemistry, University of Aveiro, Aveiro 3810-1933, Portugal.
Langmuir. 2023 Feb 21;39(7):2692-2709. doi: 10.1021/acs.langmuir.2c03176. Epub 2023 Feb 10.
Aqueous systems comprising polymers and surfactants are technologically important complex fluids with tunable features dependent on the chemical nature of each constituent, overall composition in mixed systems, and solution conditions. The phase behavior and self-assembly of amphiphilic polymers can be changed drastically in the presence of conventional ionic surfactants and need to be clearly understood. Here, the self-aggregation dynamics of a triblock copolymer (Pluronics L81, EOPOEO) in the presence of three cationic surfactants (with a 12C long alkyl chain but with different structural features), viz., dodecyltrimethylammonium bromide (DTAB), didodecyldimethylammonium bromide (DDAB), and ethanediyl-1,2-bis(dimethyldodecylammonium bromide) (12-2-12), were investigated in an aqueous solution environment. The nanoscale micellar size expressed as hydrodynamic diameter () of copolymer-surfactant mixed aggregates was evaluated using dynamic light scattering, while the presence of a varied micellar geometry of L81-cationic surfactant mixed micelles were probed using small-angle neutron scattering. The obtained findings were further validated from molecular dynamics (MD) simulations, employing a simple and transferable coarse-grained molecular model based on the MARTINI force field. L81 remained molecularly dissolved up to ∼20 °C but phase separated, forming turbid/translucent dispersion, close to its cloud point (CP) and existed as unstable vesicles. However, it exhibited interesting solution behavior expressed in terms of the blue point (BP) and the double CP in the presence of different surfactants, leading to mixed micellar systems with a triggered morphology transition from unstable vesicles to polymer-rich micelles and cationic surfactant-rich micelles. Such an amendment in the morphology of copolymer nanoaggregates in the presence of cationic surfactants has been well observed from scattering data. This is further rationalized employing the MD approach, which validated the effective interactions between Pluronics-cationic surfactant mixed micelles. Thus, our experimental results integrated with MD yield a deep insight into the nanoscale interactions controlling the micellar aggregation (Pluronics-rich micelles and surfactant-rich micelles) in the investigated mixed system.
包含聚合物和表面活性剂的水基体系是具有可调特性的技术重要的复杂流体，这些特性取决于每个组分的化学性质、混合体系中的总体组成和溶液条件。两亲聚合物的相行为和自组装在常规离子表面活性剂存在的情况下会发生剧烈变化，需要清楚地了解。在这里，在三种阳离子表面活性剂（具有 12C 长烷基链但具有不同结构特征），即十二烷基三甲基溴化铵（DTAB）、二（十二烷基二甲基）溴化铵（DDAB）和 1,2-乙二基双（二甲基十二烷基溴化铵）（12-2-12）的存在下，研究了嵌段共聚物（Pluronics L81，EOPOEO）在水溶液环境中的自组装动力学。使用动态光散射评估了作为聚合物-表面活性剂混合聚集体的水动力直径 () 的纳米级胶束尺寸，而使用小角中子散射探测了 L81-阳离子表面活性剂混合胶束的不同胶束几何形状的存在。从分子动力学 (MD) 模拟中获得的发现进一步得到验证，使用基于 MARTINI 力场的简单且可转移的粗粒度分子模型。L81 分子溶解至约 20°C，但发生相分离，形成混浊/半透明分散体，接近其浊点 (CP)，并以不稳定的囊泡形式存在。然而，在不同表面活性剂存在下，它表现出有趣的溶液行为，表现为蓝点 (BP) 和双 CP，导致混合胶束系统从不稳定的囊泡到聚合物丰富的胶束和阳离子表面活性剂丰富的胶束的形态转变。在阳离子表面活性剂存在下，共聚物纳米聚集体的形态发生了这种变化，这可以从散射数据中很好地观察到。使用 MD 方法对此进行了合理化，该方法验证了 Pluronic-cationic 表面活性剂混合胶束之间的有效相互作用。因此，我们的实验结果与 MD 相结合，深入了解控制所研究混合体系中胶束聚集（聚合物丰富的胶束和表面活性剂丰富的胶束）的纳米尺度相互作用。
