| Microemulsion (ME) is a thermodynamically stable, isotropic transparent (or translucent) oil/water dispersion system and formed spontaneously by the surfactant, cosurfactant, water (or brine), oil (hydrocarbon) and other components. This decentralized system has some characteristics, such as: dispersed phase particle size is small, ultra-low interfacial tension and so on, is widely used in the pharmaceutical, preparation of nano-materials, fuel, pesticide spraying, cosmetics, thrice oil field. Therefore, studies of microemulsion formation regularity and microemulsification technology to obtain single-phase microemulsion in the composition range as wide as possible, and to guide scientifically and effectively the design of microemulsion formulation, have important theoretical and practical significance in effectively controlling the micro-structure of microemulsion.In this paper, it is studying the microemulsification in DTAB/alcohols/oils/water systems, takes dodecyl trimethyl ammonium bromide (DTAB) as the cationic surface active agent, short chain alcohol as a co-surfactant, short chain alkane as oil,Firstly, take the phase diagram of material system as breakthrough point and the basic theory of physical chemistry and colloid surface as the basis, research the DTAB/alcohols/oils/water microemulsion phase behavior and microemulsification formation. It turned out that， km values (ratio of the amount of substances cosurfactant and surfactant), different alcohols, different oil and oil-content have a larger microemulsification effect to microemulsion phase region compared with temperature. When km=4.16, the system form a microemulsion area, with the best emulsifying effect, different chain length of alcohol, the system pseudo ternary phase diagrams and microemulsion area fraction are also different, n-propanol, isobutanol, butanol its carbon chain is relative short, which can form a continuous single-phase microemulsion phase region, n-pentanol, n-hexanol, a relative long carbon chain, and were unable to form a continuous single phase microemulsion region, but form the liquid crystal, and the microemulsion is divided into two unequal size, with continuous microemulsion region system, when Ls=La+Lo, the obtained microemulsion area is the largest, but if there is a liquid crystal, even L_s=L_a+L_o, microemulsion area is not maximum the system of the starting oil is larger, the oil carbon chain is longer (n-hexane, n-heptane, n-octane), the maximum water content in the system is smaller, the area of the microemulsion is smaller.In order to study the microstructure and its transformation process, and further draw phase diagram, by using conductivity method for the determination of microemulsion microstructure, to study microemulsion conductivity percolation mechanism.The diffusion coefficients of DTAB microemulsion were measured by using K3Fe(CN)6as the electroactive probes by using the cyclic voltammetric measurement. The microstructure and the structural conversion of the microemulsion has been determined from the water content dependence of the apparent diffusion coefficients in one-phase microemulsion region. The results show that, the conductivity method can accurately identify the three structures of microemulsion, when the system w(oil) is small, the system has a W/O type, BC type, O/W type three microemulsion structures, when w(oil) increases to a certain extent, can be observed that Φc(percolation threshold), and its value is increased with w(oil) increasing with w(oil), the system of O/W type, the BC microemulsion gradually disappear until the W/O type microemulsion occurs phase separation even doesn’t have the chance to transform into the O/W type. Cyclic voltammetry determination of microemulsion structure transition region and conductivity method is consistent.The study of microemulsion conductivity activation energy shows that the microemulsion of the W/O type conductivity activation energy reflects the energy that charged ions pass through the interface membrane and the energy needed in separating of the collision particles, O/W microemulsion conductance activation energy is the sum of the energy that charged particles of the aqueous phase of the conductive process through the micelle interface membrane and the energy required to overcome the moving resistance of the energy required and the oil phase ion.In order to obtain the micro-structure information about surfactant and co-surfactant in the oil phase and component of the interface and microemulsion droplet size, to effectively control the microemulsion droplets size for the purpose, to provide a theoretical basis for the application of the microemulsion, by using dilution method to determine function of the water content ω value, different alcohols, different oil and and temperature in the W/O microemulsion interface, thermodynamic properties and microstructure. The results show that, in all system, alcohol from the oil phase to migrate to the interface phase, ΔGc'i1<0, so it is spontaneous, but a different water content and different alcohols and different oil phase system, the migration ability of the alcohol is different. When alcohol, oil is fixed, ω value is small, then the nai is smaller, ΔG'i1absolute value is larger. With n (alcohol carbon atoms) increasing, nai was decreased, ΔGc'i1absolute value becomes larger, ΔHc'i1and ΔSc'1was decreased, and the value of co is larger, n impact on the system value ΔGc'i1is larger. With n’(alkane carbon atoms) increasing, nai was increased, ΔGc'i1absolute value was decreased, ΔHc'i1and ΔSc'i1was increased, the value of co is large, n’ impact on the system value ΔGc'i1is larger, the ΔGc'i1. absolute value of the same system increases with temperature. Within a certain temperature range, the four-component system of the DTAB/alcohols/oils/water in forming a microemulsion, when the moisture content of system is smaller, the number of carbon atoms in alcohol is increasing, the alkane carbon atom number is reducing and temperature is elevating are favorable to the formation and stability of the W/O microemulsion.The study of microemulsion structure parameters shows that, with the value of ω increasing, the Rw, Re,l, n was increased, Nd was decreased, and Ad was increased or decreased according to dominant of the system of Vd、Re. With the increasing of chain length of the alcohol, or increasing of chain length of the oil, theRw,Re, l, n was increased, but Ad, Nd was decreased. Therefore, by selecting the appropriate alcohol, oil, and changing the co value of the microemulsion system to control kernel water droplet Rw... |
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