Probing Self-assembled Micellar Topologies via Micro-scale Diffusive Dynamics of Surfactants
Probing Self-assembled Micellar Topologies via Micro-scale Diffusive Dynamics of Surfactants
复制标题
通过表面活性剂的微尺度扩散动力学探测自组装胶束拓扑
DOI：
10.1016/j.jcis.2023.03.102
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发表时间：
2023
影响因子：
9.9
通讯作者：
Mohammadigoushki, Hadi
中科院分区：
文献类型：
--
作者：
Scigliani, Alfredo;Grant, Samuel C.;Mohammadigoushki, Hadi
假设表面活性剂在水溶液中自发自组装，在能源、生物技术和环境中起着至关重要的作用。自组装胶束可能会经历超过临界反离子浓度的不同拓扑转变，但相关的机械特征是相同的。通过非侵入性的1H核磁共振扩散法监测单个表面活性剂在胶束中的自扩散动力学，我们可以区分不同的拓扑转变，以克服与传统微结构探测技术相关的挑战。实验考察了不同反离子浓度下CTAB/5MS、OTAB/NaOA和CPCl/NaClO3三种胶束体系的流变性。进行了系统的1H核磁共振扩散测量，并测量了由此产生的信号衰减。发现在没有反离子的情况下，表面活性剂在胶束中以均方位移Z 2∼T DIFF自由扩散。随着反离子浓度的增加，自扩散受到Z 2∼T Diffα和α→0.5的限制。在粘度峰之外，对于呈现线性-短线性胶束转变的OTAB/NaOA体系，Z2∼T diff 0.5。相反，对于CTAB/5MS体系，在粘度峰值以上经历了线性蠕虫-囊泡转变，恢复了自由自扩散。CPCl/NaClO3的扩散动力学与OTAB/NaOA的扩散动力学相似。因此，可以推测出类似的拓扑转变。这些结果突出了1H核磁共振扩散法对胶束拓扑转变的独特敏感性。
Hypothesis Surfactants spontaneously self-assemble in aqueous solutions and are critical in energy, biotechnology, and the environment. The self-assembled micelles may experience distinct topological transitions beyond a critical counter-ion concentration, yet the associated mechanical signatures are identical. By monitoring self-diffusion dynamics of individual surfactants in micelles via a non-invasive 1 H NMR diffusometry, we may distinguish various topological transitions overcoming challenges associated with traditional microstructural probing techniques. Experiments Three micellar systems based on CTAB/5mS, OTAB/NaOA and CPCl/NaClO 3 are considered at various counter-ion concentrations, and their rheological properties are assessed. A systematic 1 H NMR diffusometry is conducted and the resulting signal attenuation is measured. Findings With no counter-ion, surfactants self-diffuse freely with a mean squared displacement Z 2∼ T diff in the micelles. As counter-ion concentration increases, self-diffusion becomes restricted with Z 2∼ T diff α, and α→ 0.5. Beyond the viscosity peak, for the OTAB/NaOA system that shows a linear-shorter linear micelle transition, Z 2∼ T diff 0.5. Conversely, for the CTAB/5mS system that experiences a linear wormlike-vesicle transition above the viscosity peak, a free self-diffusion is recovered. The diffusion dynamics in CPCl/NaClO 3 are similar to those of OTAB/NaOA. Hence, a similar topological transition is surmised. These results highlight the unique sensitivity of the 1 H NMR diffusometry to micelles topological transitions.