Viscosities and densities for 1-butyl-3-methylimidazolium hexafluorophosphate （[C4mim][PF6]） and N, N-dimethylformamide （DMF） binary mixtures have been measured at the temperature range from 293.15 K to 318.15 K. It is shown that the viscosities and densities decrease monotonously with temperature and the content of DMF. Various correlation methods including Arrhenius-like equation, Sedclon et al.＇s equation, Redlich-Kister equation with four parameters, and other empirical equations were applied to evaluate these experimental data. A model based on an equation of state Ior estimating the viscosity of mixtures containing ionic liquids were proposed by coupling with the excess Gibbs free energy model of viscosity, which can synchronously calculate the viscosity and the molar volume. The results show that the model gives a deviation of 8.29% for the viscosity, and a deviation of 1.05% for the molar volume when only one temperature-independent adjustable parameter is adopted. The correlation accuracy is further improved when two parameters or one temperature-dependent parameter is used.
Interaction of anionic polyelectrolyte with cationic gemini surfactant has been investigated by coarse-grained molecular dynamics simulation.Polyelectrolyte facilitates the oppositely charged ionic surfactants to aggregate by suppressing the electrostatic repulsion between ionic head groups leading to the formation of micellar complex.With addition of surfactant,the conformation of polyion chain changes from stretched to random coiled to spherical,and at the same time more free micelles are formed by surfactants in mixtures.Increasing the length of spacer or tail chain in gemini surfactant will weaken its interaction with polyelectrolyte and simultaneously strengthen its tendency to self-assemble.The simulation results are consistent with experimental observations and reveal that the electrostatic interaction plays an important role in the interaction of polyelectrolyte with gemini sur- factant.
The microstructure of cationic gemini surfactant 1,6-bis(dodecyldimethylammonium) hexane dibromide C12H25(CH3)2N(CH2)6N(CH3)2C12H252Br (126122Br) and oppositely charged polyelectrolyte poly(acrylic acid, sodium salt) (NaPA) in aqueous solution has been studied by using fluorescence, conductivity measurement, freeze-etching and TEM. The data obtained from fluorescence and conductivity measurement show that micelle-like or complex can form between the gemini surfactant (126122Br) and polyelectrolyte NaPA due to the static electric interaction and hydrophobic forces. Through freeze-etching and TEM, the microstructure of the mixture solution has been studied, which is consistent with the result from micropolarity. Comparing the fluorescence spectrum of system of dodecyltrimethylammonium bromide (DTAB) and NaPA with that of system of gemini surfactant (126122Br) and NaPA, it can be found that the interaction between gemini surfactant (126122Br) and NaPA is stronger than that between DTAB and NaPA. And the phase behavior of (126122Br) and NaPA in aqueous solution has also been detected. It can be shown that the precipitate will transform into gel in higher NaPA concentration.
Surface morphologies of the films of poly [styrene-b-（ethylene-co-butene）-b-styrene] （SEBS） have been studied by using tapping-mode atomic force microscopy （TM-AFM）. The films of block copolymer were prepared both by spin-coating on mica and by solvent-casting on different solution surfaces. For spin-coating samples, the effect of solution concentration, solvent, and annealing temperature are investigated. It is shown that changing the concentration of the solution makes no difference on the morphology of the film of the block copolymer. The microstructures are quite stable during thermal annealing; only the size of the domains changes toward the equilibrium configuration. However, solvent annealing can notably change the microstructures. When different selective solvents are used for film spin-coating, different morphologies can be obtained and explained by the different solubility parameters of the solvents. As expected, significant different morphologies in the top and the bottom surfaces of the casting films were observed. The images of the top surfaces reveal cylinder microdomains, while those of the bottom surfaces were spherical morphologies.
The image contrast inversion was investigated in detail when soft polymeric materials were imaged with tapping mode atomic force microscopy （TM-AFM）. Solvent cast film of polystyrene-block-poly（ethylene/butylene）block-polystyrene （SEBS） triblock copolymers was used as a model system in this study, which showed phase separation domains with a size of several tens of nanometers. AFM contrast reversal process, through positive image, to an intermediary and till negative image, could be clearly seen in height images of the soft block copolymer using different tapping force. The higher tapping force would lead to not only contrast inversion, but also the different size of the microdomains and different roughness of the images. Moreover, contrast inversion was explained on the basis of attractive and repulsive contributions to the tip-sample interaction and indentation of the soft domains.
