离子型表面活性剂-水界面内亥姆霍兹层中反离子结合的观测
Observation of counterion binding in the inner Helmholtz layer at the ionic surfactant-water interface
AI总结：
本研究利用相敏和频振动光谱定量测定离子型表面活性剂-水界面内亥姆霍兹层的反离子吸附，推导热力学参数并构建吸附相图，揭示反离子介导界面有序化的机制，为相关领域研究提供定量探测手段。
摘要：
理解内亥姆霍兹层内的特异性离子吸附始终是电化学领域的核心问题，但在实验上难以实现。本研究利用相敏和频振动光谱（PS-SFVS，phase-sensitive sum-frequency vibrational spectroscopy）直接定量了内亥姆霍兹层内的反离子吸附，并提取了相关热力学参数。以十二烷基硫酸钠（SDS，sodium dodecyl sulfate）作为模型离子型表面活性剂，我们通过同时分析界面自由OH响应与扩散层和频信号，测定了Na+和DS-的表面密度，并由此推导得到吸附热力学参数。随后我们构建了吸附相图，描绘了致密层中Na+和DS-物种随本体NaCl浓度与SDS浓度变化的演化规律，揭示出表面离子配对现象持续增加。DS-与Na+的配对比例随NaCl浓度升高逐渐降低，在表面成核前的过饱和状态下接近2.8。这些结果确立了PS-SFVS作为带电界面中离子-头基关联定量探针的地位，揭示了反离子介导的界面有序化背后的热力学机制，对电解质设计、生物膜稳定性及软物质组装具有广泛意义。
英文摘要：
Understanding specific ion adsorption within the inner Helmholtz layer remains central to electrochemistry yet experimentally elusive. Here we directly quantify counterion adsorption and extract the associated thermodynamic parameters within the inner Helmholtz layer using phase-sensitive sum-frequency vibrational spectroscopy (PS-SFVS). Using sodium dodecyl sulfate (SDS) as a model ionic surfactant, we determine the Na+ and DS- surface densities by simultaneously analyzing interfacial free OH response and the diffuse-layer SF signal, from which the adsorption thermodynamic parameters are derived. We then construct an adsorption phase diagram that maps the evolution of Na+ and DS- species in the compact layer as functions of bulk NaCl and SDS concentrations, revealing a continuous increase in surface ion pairing. The DS-: Na+ pairing ratio gradually decreases with increasing NaCl and approaches 2.8 at the supersaturation state prior to surface nucleation. These results establish PS-SFVS as a quantitative probe of ion-headgroup correlations in charged interfaces and reveal the thermodynamic mechanism underlying counterion-mediated interfacial ordering, with broad implications for electrolyte design, biomembrane stability, and soft-matter assembly.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
