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Vibrational Spectra and Adsorption of Trisiloxane Superspreading Surfactant at Air/Water Interface Studied with Sum Frequency Generation Vibrational Spectroscopy
Jun Feng,Dan Wu,Jia Wen,Shi-lin Liu,Hong-fei Wang*
Author NameAffiliationE-mail
Jun Feng Hefei National Laboratory for Physical Sciences at Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China  
Dan Wu Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China  
Jia Wen Hefei National Laboratory for Physical Sciences at Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China  
Shi-lin Liu Hefei National Laboratory for Physical Sciences at Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei 230026, China  
Hong-fei Wang* Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China hongfei@iccas.ac.cn 
Abstract:
The C-H stretch vibrational spectra of the trisiloxane superspreading surfactant Silwet L-77((CH3)3Si-O-Si(CH3)(C3H6)(OCH2CH2)7-8OCH3)-O-Si(CH3)3) at the air/water interface are measured with the surface Sum Frequency Generation Vibrational Spectroscopy (SFG-VS). The spectra are dominated with the features from the –Si-CH3 groups around 2905 cm-1 (symmetric stretch or SS mode) and 2957 cm-1 (mostly the asymmetric stretch or AS mode), and with the weak but apparent contribution from the -O-CH2- groups around 2880 cm-1 (symmetric stretch or SS mode). Comparison of the polarization dependent SFG spectra below and above the critical aggregate or micelle concentration (CAC) indicates that the molecular orientation of the C¡H related molecular groups remained unchanged at different surface densities of the Silwet L-77 surfactant. The SFG-VS adsorption isotherm suggested that there was no sign of Silwet L-77 bilayer structure formation at the air/water interface. The Gibbs adsorption free energy of the Silwet surfactant to the air/water interface is -42.2±0.8kJ/mol, indicating the unusually strong adsorption ability of the Silwet L-77 superspreading surfactant
Key words:  Trisiloxane surfactant, Superspreader, Surface adsorption, Sum frequency generation vibrational spectroscopy
FundProject:国家自然科学基金,国家重点基础研究发展计划
Vibrational Spectra and Adsorption of Trisiloxane Superspreading Surfactant at Air/Water Interface Studied with Sum Frequency Generation Vibrational Spectroscopy
冯军,吴丹,闻佳,刘士林,王鸿飞*
摘要:
使用界面和频振动光谱(SFG-VS)测量了空气/水界面三甲基硅烷表面活性剂Silwet L-77的C-H伸缩振动光谱.这些光谱峰主要是在2905 cm-1附近属于-Si-CH3基团的对称伸缩(SS)振动,在2957 cm-1的主要是-Si-CH3基团反对称伸缩(AS)振动,以及明显较弱的在2880 cm-1附近的属于-O-CH2-基团的对称伸缩(SS)振动.通过比较低于和高于临界聚集或胶束浓度(CAC)的SFG-VS偏振光谱显示Silwet L-77分子的C-H基团取向在不同的界面密度下变化很小.SFG-VS测量的吸附等温线表明Silwet L-77分子在空气/水界面没有形成所谓的双层结构的迹象.Silwet L-77分子在空气/水界面的Gibbs吸附自由能为-42.2±0.8 kJ/mol,表明该分子具有很强的表面吸附能力.
关键词:  三甲基硅烷表面活性剂,超铺展性,表面吸附,和频振动光谱
DOI:10.1088/1674-0068/21/04/314-323
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