Experimental and Theoretical Studies on the Self-assembled Nano-structure of Nonionic Surfactant/ionic Liquid Hybrid Systems

Abstract The self-assembled structure of various Brij series nonionic surfactants (such as Brij-30, Brij-52, Brij-56, Brij-58, Brij-35, and Brij-700) hybridized with room-temperature ionic liquids (RTILs) was studied using small-angle X-ray scattering (SAXS) measurements and DFT calculations. The detailed characterization of the obtained self-assembled structure in nonionic surfactant/RTILs hybrid system was carried out using the combination of SAXS and DFT calculations. The SAXS result indicates that the alkyl chain length dependence on the spatial correlation corresponds to the interference peak angle. The addition of Brij surfactant to the [BMIm][PF 6 ] results in a drastic change in the interference peak position. The DFT calculation result shows that a weak hydrogen bonding was formed between the −CH, −F of RTIL s ([BMIm][PF 6 ] and [OMIm][PF 6 ]) and the polar site −OH, −O − of surfactants (Brij-30 and Brij-56). When the mixing molar ratio of ILs/Brij is 1:1, the absolute value of interaction energy (Δ E 0 BSSE ) is 8.10-1.43 and 4.22-0.90 kcal·mol -1 for ILs/Brij-30 and ILs/Brij-56, respectively. Meanwhile, in the case of the ILs/Brij molar ratio equal to 2:1, Δ E 0 BSSE is 19.14-1.79 and 12.39-1.45 kcal·mol -1 , respectively. It suggests that the stability of ILs/Brij hybridized system is higher for ILs/Brij-30 than for ILs/Brij56, and it has an increasing tendency to some extent with an increase of the molar fraction of ILs.