Coassembly of Poly(ethylene glycol)-block-Poly(glutamate sodium) and Gemini Surfactants with Different Spacer Lengths

Yuchun Han, Wentao Wang, Yongqiang Tang, Shusheng Zhang, Zhibo Li,* and Yilin Wang*

Langmuir 2013, 29, 9316−9323

The coassembly of poly(ethylene glycol)-b-poly-(glutamate sodium) copolymer (PEG₁₁₃-PGlu₁₀₀) with cationicgemini surfactants alkanediyl-α,ω-bis-(dodecyldimethylammoniumbromide) [C₁₂H₂₅(CH₃)₂N(CH₂)_SN(CH₃)₂C₁₂H₂₅]Br₂ (designated as C₁₂C_SC₁₂Br₂, S = 3, 6, and 12) have been studied by isothermal titration microcalorimetry, cryogenic transmission electron microscopy, circular dichroism, small-angle X-ray scattering, zeta potential, and size measurement. It has been shown that the electrostatic interaction of C₁₂C_SC₁₂Br₂ with the anionic carboxylate groups of PEG₁₁₃-PGlu₁₀₀ leads to complexation, and the C₁₂C_SC₁₂Br₂/ PEG₁₁₃-PGlu₁₀₀ complexes are soluble even at the electroneutral point. The complexes display the feature of superamphiphiles and assemble into ordered nanosheets with a sandwich-like packing. The gemini molecules which were already bound with PGlu chains associate through hydrophobic interaction and constitute the middle part of the nanosheets, whereas the top and bottom of the nanosheets are hydrophilic PEG chains. The size and morphology of the nanosheets are affected by the spacer length of the gemini surfactants. The average sizes of the aggregates at the electroneutral point are 81, 68, and 90 nm for C₁₂C₃C₁₂Br₂/ PEG₁₁₃-PGlu₁₀₀, C₁₂C₆C₁₂Br₂/ PEG₁₁₃-PGlu₁₀₀, and C₁₂C₁₂C₁₂Br₂/ PEG₁₁₃-PGlu₁₀₀, respectively. Both C₁₂C₃C₁₂Br₂/ PEG₁₁₃-PGlu₁₀₀ and C₁₂C₁₂C₁₂Br₂/ PEG₁₁₃-PGlu₁₀₀ mainly generate hexagonal nanosheets, while the C₁₂C₆C₁₂Br₂/ PEG₁₁₃-PGlu₁₀₀ system only induces round nanosheets.