Acta Chimica Sinica ›› 2014, Vol. 72 ›› Issue (1): 41-50.DOI: 10.6023/A13111118 Previous Articles     Next Articles



王瑞娟, 王毅琳   

  1. 中国科学院化学研究所 北京 100190
  • 投稿日期:2013-11-01 发布日期:2013-12-17
  • 通讯作者: 王毅琳,;Tel.:010-82615802;Fax:010-82615802
  • 基金资助:

    项目受国家自然科学基金(Nos. 21025313,21021003)资助.

Interaction of Anionic Sulfonate Gemini Surfactant with PEO-PPO-PEO Triblock Copolymers

Wang Ruijuan, Wang Yilin   

  1. Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190
  • Received:2013-11-01 Published:2013-12-17
  • Supported by:

    Project supported by the National Natural Science Foundation of China (Nos. 21025313, 21021003).

The interaction of anionic sulfonate gemini surfactant 1,3-bis(N-dodecyl-N-propylsulfonate sodium)-propane (12-3-12(SO3)2) with two triblock copolymers poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), F127 (EO97PO69EO97) and P123 (EO20PO70EO20) having the similar hydrophobic PPO central block but with different hydrophilic PEO end block, has been studied in aqueous solution at pH 9 by using differential scanning calorimetry (DSC), isothermal titration calorimetry (ITC), dynamic light scattering (DLS) and NMR techniques. At pH 9, the sulfonate groups of 12-3-12(SO3)2 are completely deprotonated and each molecule carries two negative charges as an anionic gemini surfactant. DSC measurements have shown that the critical micellar temperature (CMT) of the two copolymers decreases as the 12-3-12(SO3)2 concentration increases. Moreover, at intermediate 12-3-12(SO3)2 concentrations, there appear two overlapping endothermic peaks, which is related to the aggregate transition between micelles with different sizes and microstructures, which has been substantiated by the DLS and NMR (spin-lattice (T1) and spin-spin (T2) relaxation times, and two-dimensional nuclear Overhauser effect spectroscopy (2D NOESY)) measurements. Compared with traditional single-chain ionic surfactants, the anionic gemini surfactant 12-3-12(SO3)2 has a much stronger ability of lowering the CMT of copolymers, which should be attributed to the stronger aggregation ability and the lower critical micellar concentration of 12-3-12(SO3)2. Furthermore, a combination of experiments involving ITC and DLS has shown that 12-3-12(SO3)2 binds to the two copolymers at temperatures below and above their CMT. At the temperature below their CMT, the 12-3-12(SO3)2 micelles form complex with monomeric copolymer, which is similar to that observed in the traditional single-chain ionic surfactant/copolymer systems, but the critical aggregation concentration for the onset of 12-3-12(SO3)2 binding to the two copolymers is very low. At temperatures above their CMT, the association of 12-3-12(SO3)2 with a mixture of monomeric and micellar copolymer or micellar copolymer leads to the formation of mixed copolymer/12-3-12(SO3)2 micelles within copolymers and then breakdown of mixed micelles into smaller mixed micelles, but the mixed copolymer/surfactant micelles have not been completely disrupted. Moreover, at high 12-3-12(SO3)2 concentrations, the hydrodynamic radii (Rh) of F127/12-3-12(SO3)2 micelles level off, while the Rh of P123/12-3-12(SO3)2 micelles have a gradual increase. The increase of Rh might be accounted for the increase in micellar weight or aggregation number.

Key words: gemini surfactant, block copolymer, interaction, differential scanning calorimetry, isothermal titration calorimetry