Oil/surfactant ratios

Nanoemulsions can be prepared starting from microemulsions located in the inverse microemulsion domain, Oj, and in the direct microemulsion domain, W, at different oil surfactant ratios ranging from 12 88 to 40 60, and coincident for both types of microemulsion. The water concentration is fixed at 20% for microemulsions in the domain labelled as O l, 0 2, 0 3, 0 4, and 0 5. The microemulsions in the region are accordingly W 2, W 3, W 4, and W 5, and their water content was decreased from W 2 to W 5. 

When the oil/surfactant ratio is decreased (by ca. 35%), the diffusion coefficient as a function of concentration is much different. At low concentrations of aggregates. 

Small columns with an inner diameter of 17 nun were packed with dry sand resulting in sand columns with an approximate volume of 10 cm and an average porosity of 24%. Oil was added onto the top of these columns and flushed after 15 min discontinuously with portions of 1) 1 w % surfactant solution and 2) 100 cm water. Surfactant solutions and water moved through the columns simply by gravitation. The oil/surfactant ratio was 1. Flow rate was monitored and the residual oil concentration in soil was determined. 

Figure 11.2 Apparent order parameter, S, and isotropic hypeifine splitting, a, of 5-doxylstearic acid as a function of water content in water/C,2EOf cyclohexane and water/CnEOfcyclohexane systems, a and b denote the solubilization limits in CnEOs and Ci EO systems, respectively. The oil/surfactant ratio in the C EOs system is 1.5 and in the C16EO4 system is 1.63 (Reproduced by permission of the American Chemical Society from ref. 27)...

Several factors that modulate the release and diffusion in gel emulsions have been studied, namely dispersed phase volume fi-action, oil/surfactant ratio, electro-... 

Figure 11.13a shows a microemulsion of the 0.1 M NaCI aqueous solution/Ci2E4/ decane system with 90% aqueous solution and an oil/surfactant ratio of 2.33, at 7°C. The HLB temperature of this system is approximately 18 C. When the sample is rapidly brought to a higher temperature, 40 C in the experiment shown in Figure 11.13b, the sample becomes milky in less than 40 s. If the test tube is inverted, no flow is observed, an indication that complete emulsification has been achieved. The emulsions produced by this emulsification method have finer and narrower droplet size distributions (Figure 11.14) than those obtained by the usual methods. 

Surfactants for Mobility Control. Water, which can have a mobihty up to 10 times that of oil, has been used to decrease the mobihty of gases and supercritical CO2 (mobihty on the order of 50 times that of oil) used in miscible flooding. Gas oil mobihty ratios, Af, can be calculated by the following (22) ... 

In view of these potentials for major reductions in preservative efficacy, considerable effort has gone into attempts to devise equations in which one might substitute variously derived system parameters such as partition coefficients, surfactant and polymer binding constants and oil water ratios in order to obtain estimates of residual preservative levels in aqueous phases. Although some modestly successful predictions have been obtained for very simple laboratory systems, they have proved of limited practical value as data for many of the required parameters are unavailable for technical grade ingredients or for the more complex commercial systems. 

The formation of ethylcellulose nanoemulsions by a low-energy method for nanoparticle preparation was reported recently. The nanoemulsions were obtained in a water-polyoxyethylene 4 sorbitan monolaurate-ethylcellulose solution system by the PIC method at 25 °C [54]. The solvent chosen for the preparation of the ethylcellulose solution was ethyl acetate, which is classed as a solvent with low toxic potential (Class 3) by ICH Guidelines [78]. Oil/water (O/W) nanoemulsions were formed at oil/ surfactant (O/S) ratios between 30 70 and 70 30 and water contents above 40 wt% (Figure 6.1). Compared with other nanoemulsions prepared by the same method, the O/S ratios at which they are formed are high, that is, the amount of surfactant needed for nanoemulsion preparation is rather low [14]. For further studies, compositions with volatile organic compound (VOC) contents below 7 wt% and surfactant concentrations between 3 and 5 wt% were chosen, that is, nanoemulsions with a constant water content of 90% and O/S ratios from 50 50 to 70 30. 

Pons et al. have studied the effects of temperature, volume fraction, oil-to-surfactant ratio and salt concentration of the aqueous phase of w/o HIPEs on a number of rheological properties. The yield stress [10] was found to increase with increasing NaCl concentration, at room temperature. This was attributed to an increase in rigidity of films between adjacent droplets. For salt-free emulsions, the yield stress increases with increasing temperature, due to the increase in interfacial tension. However, for emulsions containing salt, the yield stress more or less reaches a plateau at higher temperatures, after addition of only 1.5% NaCl. 

Viscosity. This parameter can be monitored by standard rheological techniques. The rheological properties of emulsions, reviewed by Sherman (1983), can be complex, and depend on the identity of surfactants and oils used, ratio of disperse and continuous phase, particle size, and other factors. Flocculation will generally increase viscosity thus, monitoring viscosity on storage will be important for assessing shelf-life. 

Microemulsions are stable, clear suspensions of two immiscible liquids and a surfactant. The surfactant forms a monolayer with its hydrophilic head dissolved in the water and its hydrophobic tail in the oil. The ratio between the three and the addition of salts, other liquids, or co-surfactants allow for fine tuning of the size of the droplets, which typically range from 5 to 100 nm. 

The Kahlweit fish, however, is only a special case for a fixed water/oil ratio of an even more complex phase behaviour of the ternary system water/oil/surfactant. The more general... 

For given values of the control variables Xsw and. Xaw, the maximum in Xgo (or Xgw) was found, using the IMSL subroutine ZXMWD, by solving the implicit eq 3.1 in combination with eq 3.4. As mentioned in section 2, the area per surfactant molecule a, the alcohol-to-surfactant ratio gAi4 si, and the oil-to-surfactant ratio golgsi in the interfacial layer were selected as the three independent variables with respect to which the maximization was carried out. The total volume fraction 4>s of surfactant present in the microemulsion is given by... 

The maximum of Qf is determined with respect to the two independent variables, the area per surfactant molecule of the interface, aF, and the alcohol-to-surfactant ratio in the interfacial layer, (gAs/gsih- In contrast to that in the droplet-type microemulsion, the oil-to-surfactant ratio in the interfacial layer, (goi/gsi)F, is not an independent variable but is determined by the packing constraint (eq 2.7) for flat layers. 

Nanocapsule/nanosphere size ranges between 200 and 350 nm were observed to be affected by both the oil-ethanol ratio and the oil-monomer ratio [63, 64], It is also influenced by the particular oil, water-miscible organic solvent, and nonionic surfactant in the aqueous phase. The pH of the aqueous phase and the temperature also affect the size distribution. 

The microemulsion method utilizes a water/oil/surfactant system to construct a micro reactor, in which NCs could be s)mthesized. The microemulsions have a wide range of applications from oil recovery fo fhe s)mfhesis of nanoparticles. Microemulsion is a system of water, oil, and surfactant, and it is an optically isotropic and thermod3mamically stable solution. At molecular scale, the microemulsion is heterogeneous with an internal structure either of nanospherical monosized droplefs (micelles or reverse micelles) or a bicontinuous phase, depending on the given temperature as well as the ratio of its constituents (Eriksson et al., 2004). The small droplets could be utilized as microreactors in order to s)mthesize the fine NCs in a controllable way. 

Dispersion Formation, Subdivision, and Coalescence. The ability to create and control dispersions at distances far from the injection well will be critical to the field-use of dispersion-based mobility control. The early studies of Bernard and Holm, followed by more recent work by Hirasaki, Falls, and co-workers, and others showed that the flow properties of surfactant-induced dispersions depend on the presence and composition of oil, volume ratio of the dispersed and continuous phases, capillary pressure, and capillary number (35,37,39-41,52-54,68). However, it is the size of the droplets or bubbles that dominates dispersion flow (39,68). Moreover, early debates on the ratio of droplet (or bubble) size to pore size have been resolved by ample evidence showing that, under commonly employed conditions, droplets are larger than pores (39). Only for very large capillary numbers (i.e., for interfacial tensions of ca. 

With increased surfactant/(cosurfactant + surfactant) ratio (0.22), the liquid crystal was formed immediately and the interface in the oil layer now lasted only 12 days, (Fig. 4). The formation of a liquid crystal impeded the transport of surfactant to the lower part. Fig. 5A. In this case, the surfactant concentration remained lower in the bottom layers during the entire duration of the experiment more than 2 months. The transport of cosurfactant to lower parts. Fig. 5B, and water from the layers below the liquid crystal. Fig. 5C, were not influenced to a great degree by the enhanced amount of liquid crystal. 

The nonlonlc microemulsion used is a well characterized aizjA) nonionic mlcroemulslon with Brij-96 (oleyl-10 ethoxylate) as the primary surfactant, n-butanol as the cosurfactant and hexadecane in the weight ratio of 5.32/2.78/0.90. When diluted with water to 9Z, oil + surfactant + cosurfactant, this forms a water clear mlcroemulslon having a sharp cloud point of about 58 C. The cloud point of this mlcroemulslon is depressed to about 51 C when the external phase is 2 wt X NaCl in water. 

The amount of water added to a water-in-oil (w/o) microemulsion is defined by the molar water-to-surfactant ratio, W. Generally, the greater the W value, the larger the size of the nanometer-sized... 

Crude oil and brine pumps may be centrifugal or positive displacement, but must be capable of providing steady flow to the mixing device because emulsion properties are highly dependent on the resulting crude-oil-brine ratio. Surfactant may be dissolved in the brine phase on a batch or continuous basis. Static mixers provide a simple method for the preparation step because they require no moving parts, are easy to scale up, and provide an mixing intensity that is suited to preparation of transport emulsions. 

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