Investigation of the interfacial water structure on poly[2-(dimethylamino)ethyl methacrylate] at the air/water interface by sum frequency generation vibrational spectroscopy  

作　　者：WU Dan GUO Yuan LIU GuangMing ZHANG GuangZhao 

机构地区：[1]Graduate University of the Chinese Academy of Sciences, Beijing 100049, China [2]Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, the Chinese Academy of Sciences, Beijing 100190, China [3]Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei 230026, China

出　　处：《Chinese Science Bulletin》2012年第9期984-991,共8页

基　　金：supported by the Main Direction Program of Knowledge Innovation of Chinese Academy of Sciences (KJCX-EW-W09);the National Natural Science Foundation of China (91027042,21073199)

摘　　要：The effect of pH on the conformation of surface alkyl groups and the structure of interfacial water molecules on poly[2-(dime-thylamino)ethyl methacrylate](PDEM) at the air/water interface were investigated with sum frequency generation vibrational spectroscopy(SFG-VS).At pH 4.1,the hydrogen bonding SFG spectra were similar to that of the air/pure water interface.As the pH increased from 5.4 to 9.6,the SFG intensities of both highly ordered hydrogen bonding(3200 cm-1 band) and less-ordered hydrogen bonding(3400 cm-1 band) were enhanced because of the charge-induced effect of deprotonated PDEM.The free OH peak disappeared completely because it was replaced by interfacial PDEM molecules.At pH 11.5,a new spectral band appeared at about 3580 cm-1 in the ppp and sps spectra,and this could be assigned to the C2v asymmetric stretching mode of the water molecules through molecular symmetry simulation.These hydrogen bonding structures are fully consistent with the conformational change of PDEM alkyl groups,and PDEM molecules act as a Hofmeister solvent.PDEM molecules are kosmotropic when they are charged and become more chaotropic as the pH increases.The effect of pH on the conformation of surface alkyl groups and the structure of interfacial water molecules on poly[2-（dime- thylamino）ethyl methacrylate] （PDEM） at the air/water interface were investigated with sum frequency generation vibrational spectroscopy （SFG-VS）. At pH 4.1, the hydrogen bonding SFG spectra were similar to that of the air/pure water interface. As the pH increased from 5.4 to 9.6, the SFG intensities of both highly ordered hydrogen bonding （3200 cm-1 band） and less-ordered hydrogen bonding （3400 cm-1 band） were enhanced because of the charge-induced effect of deprotonated PDEM. The free OH peak disappeared completely because it was replaced by interfacial PDEM molecules. At pH 11.5, a new spectral band appeared at about 3580 cm-1 in the ppp and sps spectra, and this could be assigned to the C2v asymmetric stretching mode of the water molecules through molecular symmetry simulation. These hydrogen bonding structures are fully consistent with the conforma- tional change of PDEM alkyl groups, and PDEM molecules act as a Hofmeister solvent. PDEM molecules are kosmotropic when they are charged and become more chaotropic as the pH increases.

关 键 词：空气/水界面 甲基丙烯酸乙酯 和频振动光谱 水结构 二甲氨基 分子结构 pH值 分子对称性 

分 类 号：O484.5[理学—固体物理] TQ225.241[理学—物理]