Surfactant solutions temperature

Small micelles in dilute solution close to the CMC are generally beheved to be spherical. Under other conditions, micellar materials can assume stmctures such as oblate and prolate spheroids, vesicles (double layers), rods, and lamellae (36,37). AH of these stmctures have been demonstrated under certain conditions, and a single surfactant can assume a number of stmctures, depending on surfactant, salt concentration, and temperature. In mixed surfactant solutions, micelles of each species may coexist, but usually mixed micelles are formed. Anionic-nonionic mixtures are of technical importance and their properties have been studied (38,39). 

The aqueous micellai solutions of some surfactants exhibit the cloud point, or turbidity, phenomenon when the solution is heated or cooled above or below a certain temperature. Then the phase sepai ation into two isotropic liquid phases occurs a concentrated phase containing most of the surfactant and an aqueous phase containing a surfactant concentration close to the critical micellar concentration. The anionic surfactant solutions show this phenomenon in acid media without any temperature modifications. The aim of the present work is to explore the analytical possibilities of acid-induced cloud point extraction in the extraction and preconcentration of polycyclic ai omatic hydrocai bons (PAHs) from water solutions. The combination of extraction, preconcentration and luminescence detection of PAHs in one step under their trace determination in objects mentioned allows to exclude the use of lai ge volumes of expensive, high-purity and toxic organic solvents and replace the known time and solvent consuming procedures by more simple and convenient methods. 

The Krafft point has practical implications for the solubility of surfactants. Only above the Krafft temperature can concentrated surfactant solutions be prepared. Otherwise, on cooling a hot surfactant solution a sudden precipitation may occur. A linear correlation between the Krafft temperature TK (°C) and the carbon number nc of sodium alkanesulfonates C10-C22 is given by the following equation ... 

Viscosity of surfactant solutions depends on the kind of solution, shear rate, temperature and concentration. Figure 2.51 shows the effect of shear rate U5 on shear... 

Thermal conductivity and capacity of aqueous surfactant solutions in the concentration range 130 to 1,060 ppm did not differ from that of pure water (Hetsroni et al. 2001b). Figure 2.53 shows the dependence of thermal conductivity k on the temperature for C = 530 ppm Habon G solution. The value of the thermal conductivity agrees well with that for pure water within the standard deviation of 2%. 

For example, for alkyl (8-16) glycoside (Plantacare 818 UP) non-ionic surfactant solution of molecular weight 390 g/mol, an increase in surfactant concentration up to 300 ppm (CMC concentration) leads to a significant decrease in surface tension. In the range 300 < C < 1,200 ppm the surface tension was almost independent of concentration. In all cases an increase in liquid temperature leads to a decrease in surface tension. This surface tension relaxation is a diffusion rate-dependent process, which typically depends on the type of surfactant, its diffusion/absorption kinetics, micellar dynamics, and bulk concentration levels. As the CMC is approached the absorption becomes independent of the bulk concentration, and the surfactant... 

The plot of the pressure drop depending on the bulk velocity in adiabatic and diabatic flows is shown in Fig. 3.6a,b. The data related to the adiabatic flow correspond to constant temperature of the fluids Tjn = 25 °C, whereas in the diabatic flow the fluid temperature increased along micro-channel approximately from 40 to 60 °C. It is seen that in both cases the pressure drop for Habon G increases compared to clear water. The difference between pressure drop corresponding to flows of a surfactant solution and solvent increases with increasing bulk velocity. 

The temperatures on the heater rw,0NB. and heat fluxes onb corresponding to onset of nucleate boiling in water and surfactant solution that contain dissolved gases are presented in Table 6.5. 

As can be seen in Table 6.5, ONB in APG solution of concentration C = 100 ppm took place at significantly higher surface temperatures. It should be noted that the ONB in surfactant solutions may not be solely associated with static surface tension Sher and Hetsroni (2002). Other parameters such as heat flux, mass flux, kind of surfactant, surface materials, surface treatments, surface roughness, dynamic surface tension and contact angle need to be considered as well. 

Surfactant blends of interest will exhibit clouding phenomena in aqueous solutions undergoing a phase transition from a one phase system to a two phase system at a discrete and characteristic temperature, referred to as the Cloud Point (CP). This value indicates the temperature at which sufficient dehydration of the oxyethylene portion of the surfactant molecule has occurred and this results in its "displacement" from solution. The addition of lyotropic salts will depress the CP, presumably due to the promotion of localised ordering of water molecules near the hydrophilic sheath of the surfactant molecule (8). Furthermore, the addition of different oils to surfactant solutions can induce either an elevation or a depression of the recorded CP and can be used to qualitatively predict the PIT (8x9). 

Surfactant molecules can be considered as building blocks for certain forms of geometry in colloidal chemistry. Various forms of association molecules can be obtained as the concentration of surfactant in water is increased and/or physicochemical conditions are changed (e.g. CMC, Craft-point, etc.). Figure 2 schematically shows the most likely structural configurations and assemblages of surfactants association in an aqueous system (26). Upon addition of oil and a short-chain alcohol, for example, one can convert the oil-in-water micelles into water-in-oil microemulsions. It is therefore possible to induce a transition from one structure to another by changing the physicochemical conditions such as temperature, pH and addition of mono or di-valent cations to the surfactant solution. It should be also noted that the sur-... 

High pressure equipment has been designed to measure foam mobilities in porous rocks. Simultaneous flow of dense C02 and surfactant solution was established in core samples. The experimental condition of dense CO2 was above critical pressure but below critical temperature. Steady-state CC -foam mobility measurements were carried out with three core samples. Rock Creek sandstone was initially used to measure CO2-foam mobility. Thereafter, extensive further studies have been made with Baker dolomite and Berea sandstone to study the effect of rock permeability. 

MCM-41 spheres were prepared modifying the procedure reported by Grim et. al. [9], using n-hexadecyltrimethylammonium bromide (Ci6TMABr) as surfactant template. Reactant molar ratio was 1 TEOS 0,3 C TMABr 0,129 NH3 144 H20 58 EtOH with pH about 9. The surfactant (Ci6TMABr) was dissolved into the mixture of distilled water, NH3 and EtOH tetraethylorthosilicate ([C2H50]4Si, TEOS) was then added to the surfactant solution and stirred for 2 hours at room temperature. 

These dyes have affinity for one or, usually, more types of hydrophobic fibre and they are normally applied by exhaustion from fine aqueous dispersion. Although pure disperse dyes have extremely low solubility in cold water, such dyes nevertheless do dissolve to a limited extent in aqueous surfactant solutions at typical dyeing temperatures. The fibre is believed to sorb dye from this dilute aqueous solution phase, which is continuously replenished by rapid dissolution of particles from suspension. Alternatively, hydrophobic fibres can absorb disperse dyes from the vapour phase. This mechanism is the basis of many continuous dyeing and printing methods of application of these dyes. The requirements and limitations of disperse dyes on cellulose acetate, triacetate, polyester, nylon and other synthetic fibres will be discussed more fully in Chapter 3. Similar products have been employed in the surface coloration of certain thermoplastics, including cellulose acetate, poly(methyl methacrylate) and polystyrene. 

Many different types of interaction can induce reversible phase transitions. For instance, weak flocculation has been observed in emulsions stabilized by nonionic surfactants by increasing the temperature. It is well known that many nonionic surfactants dissolved in water undergo aphase separation above a critical temperature, an initially homogeneous surfactant solution separates into two micellar phases of different composition. This demixtion is generally termed as cloud point transition. Identically, oil droplets covered by the same surfactants molecules become attractive within the same temperature range and undergo a reversible fluid-solid phase separation [9]. 

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