Baglioni Piero, Braccalenti Elena, Carretti Emiliano, Germani Raimondo, Goracci Laura, Savelli Gianfranco, Tiecco Matteo
CEMIN, Center of Excellence on Innovative Nanostructured Materials, Department of Chemistry, University of Perugia, Via Elce di Sotto 8, I-06123 Perugia, Italy.
Langmuir. 2009 May 19;25(10):5467-75. doi: 10.1021/la900465h.
The effect of the surfactant structure on the mechanical and structural properties of surfactant based photorheological fluids are presented in this paper. Cetyltrimethylammonium bromide (CTABr) mixed with trans-o-methoxycinnamic acid in a basic environment can form photosensitive systems. The driving force is the ability of surfactant molecules to form wormlike micelles in the presence of the anionic photosensitive additive. Taking into account that slight changes in the surfactant monomer's structure can induce drastic modifications of the micellar aggregate features, the role the of the nature of the counterion (in the CTAX type surfactants) or the headgroup size (CTRABr type surfactants) and its influence on the mechanical properties of surfactant based photorheological fluids using trans-o-methoxycinnamic acid (trans-OMCA) as additive were investigated. Rheological studies reported in this paper show that the viscosity of these systems drastically varies only by changing the nature of the surfactant counterion. Moreover, by increasing the bulk simply by replacing the three methyl groups with three ethyl groups in the surfactant headgroup moiety, the viscosity drastically decreases. Highly photosensitive PR fluids can be further obtained using cetyltrimethylammonium trans-o-methoxycinnamate (CTAOMC) as surfactant at neutral pH. In addition to the complete rheological characterization carried out by means of the application of both a steady shear and a dynamic shear stress, a 1H NMR and NOESY study was also performed.
本文介绍了表面活性剂结构对基于表面活性剂的光流变流体的力学和结构性能的影响。十六烷基三甲基溴化铵（CTABr）在碱性环境中与反式邻甲氧基肉桂酸混合可形成光敏体系。驱动力是表面活性剂分子在存在阴离子光敏添加剂的情况下形成蠕虫状胶束的能力。考虑到表面活性剂单体结构的微小变化会引起胶束聚集体特征的剧烈改变，研究了抗衡离子的性质（在CTAX型表面活性剂中）或头基大小（CTRABr型表面活性剂）的作用及其对以反式邻甲氧基肉桂酸（反式OMCA）为添加剂的基于表面活性剂的光流变流体力学性能的影响。本文报道的流变学研究表明，这些体系的粘度仅通过改变表面活性剂抗衡离子的性质就会发生剧烈变化。此外，通过在表面活性剂头基部分简单地用三个乙基取代三个甲基来增加体积，粘度会急剧降低。在中性pH下使用十六烷基三甲基铵反式邻甲氧基肉桂酸酯（CTAOMC）作为表面活性剂可进一步获得高感光度的光流变流体。除了通过施加稳态剪切和动态剪切应力进行完整的流变学表征外，还进行了1H NMR和NOESY研究。
