Study On Colloid And Micro-rheological Prtxerties Of Microemulsion Systems

Microemulsions are thermodynamically stable one-phase mixtures formed spontaneously by surfactant,oil and water,and have been widely used in many fields,such as petrochemical industry,chemical polymer:ization,nano-particles preparation,separation and purification of proteins,drug release,hydrometallurgy and so on.Ionic liquids(IL),known as green solvent,have the advantages of low melting point,non volatile,non flammable,good stability,easy separation from the product and easy recovery,and have important application prospect in above fields.However,the disadvantages of IL are high viscosity,high cost,and poor solubility of some compounds.As the same as water,ionic liquids are polar solvents,and also may form microemulsions which called ionic liquid microemulsions(ILMe)by mixed with surfactant and oil.the ILMe have lower viscosity,lower cost and improved the solubility of some compounds compared with themselves.The structure,size and rheology of microemulsion droplets play important roles on the application of microemulsions.The size of the microemulsion droplets determined by the dynamic light scattering method.Since the size of the microemulsion droplets size is usually only in the range of a few nanometers to dozens of nanometers in diameter,the scattering light produced too weak to be detected by using traditional dynamic light scattering instrument.The signal to noise ratio can be enhanced by using the 3D light scattering technique,the 3-dimensional dynamic light scattering instrument(3DDLS).The powerful of this technique is that it uses two simultaneous light scattering experiments performed at the same scattering vector on the same sample volume in order to extract only the single scattering information common to both.The correlation of the measured scattered intensities from both experiments with each other results in a cross correlation function where onlysingle scattering event cont ribute to the signal.Diffusion spectrometer instrument(DWS)is non-intrusive optical technique,can be used to measure viscoelastic properties of the samples.By measuring the intensity of multiple scattering light,the intensitycorrelation function,mean square displacement(MSD)and the micro rheological properties such as local energy storage modulus G',loss modulus G"can beobtained.Compared with the mechanical rheometer,the advantages of DWS are that the samples would not be interfered and damaged during the experiment,the measurement can be conducted in a wide frequency range,and less sample consumption.In this paper,the colloid properties and micro heological properties of two types of ILMes,i.e.[Bmim]PF6/TX-10/Cyclohexane,[Bmim]BF4/TX-10/Cyclohexane and a nonionic microemulsion system,i.e.(TX-4+TX-7)/decane/water are studied by 3D DLS and DWS methods.The main results are as follows:1.Both ILMes have similar colloidal properties and rheological properties,which are determined mainly by imidazole cation group[Bmim]+,and have less relation with the anionic groups PF6-,BF4-.2.Relationships between hydrodynamic radius(RH)and mass fraction of polar components.RH increases with increasing of mass fractions of[Bmim]PF6 or[Bmim]BF4 for both ILMes,and decreases with increasing of mass fraction of water for(TX-4+TX-7)/decane/H20 system.3.Effect of temperature on hydrodynamic radius(RH).RHdecreases with the increase of temperature for both ILMes,but increases with the increase of temperature for(TX-4+TX-7)/decane/H2O system.4.Micro-rheological properties.Both ILMes and the(TX-4+TX-7)/decane/H2O system only have loss modulus G",which show that these three microemulsions are pure viscous fluid.5.Formation mechanism.For ILMes,the formation mechanism may be described as following:at first,the oil(cyclohexane)is dissolved in the mixture micelle composed of IL and TX-10,and form O/IL single phase solution.Then with the adding of oil continuously,both oil and IL become bicontinuous phase,Afterwords,oil becomes the continuous phase,and TX-10 reverse micelle form,IL is dissolved in the reverse micelle core and lastly form IL/O microemulsion with single phase.For nonionic microemulsion(TX-4+TX-7)/decane/H20,the formation mechanismphase change process and is supposed as following:At first,the water molecule was dissolved in palisade layer of reverse micelles via hydrogen bonding,then further dissolved in reverse micelle to form unsaturation reverse micelle,saturation reverse micelle,and swell reverse micelle successively,i.e.W/O microemulsion.