Processes involving in solution a reduced number of molecules are difficult to identify and characterize. Here, we show that micellization of standard surfactants, namely sodium dodecyl sulfate and trimethyl tetradecyl ammonium bromide, two nonefficient compounds for quadratic nonlinear optics, can be investigated by second harmonic scattering (SHS). In particular, the formation of aggregates at concentrations smaller than the critical micellar concentration is evidenced through a nonmonotonic behavior of the SHS intensity as a function of the surfactant concentration. A simple model based on chemical equilibria between monomers and micelles is proposed to account for the experimental observations. Signature of long-range molecular orientation correlation is revealed by polarization resolved experiments and is discussed regarding micellization and charge-induced effects.

中文翻译：

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二次谐波散射证​​明标准表面活性剂的多步胶束化

涉及到溶液中分子数量减少的过程难以识别和表征。在这里，我们展示了标准表面活性剂的胶束化，即十二烷基硫酸钠和三甲基十四烷基溴化铵，这两种用于二次非线性光学的无效化合物，可以通过二次谐波散射 (SHS) 进行研究。特别是，在小于临界胶束浓度的浓度下形成聚集体是通过作为表面活性剂浓度函数的 SHS 强度的非单调行为证明的。提出了一个基于单体和胶束之间化学平衡的简单模型来解释实验观察。