Viscosity of surfactant solutions

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... 

Figure 21. Effect of sodium hydroxide on the low-shear Newtonian viscosity of surfactant solutions containing 0.5 and 1 wt% Neodol 25-3S.

Equation (10.1) shows that the viscosity of surfactant solutions starts to increase linearly with the concentration above the CMC. This allows in principle for a determination of the CMC by means of viscosity measurements, provided that a sufficiently precise determination of the viscosity is being carried out (since the increase of viscosity is modest even for rather high volume fractions of 0.1). 

As the concentration is increased, the viscosity of the solution generally increases, although not linearly, and may eventually undergo a sudden decrease. This is due to changes in the internal geometry of the surfactant molecules. At relatively low concentrations the alcohol ether sulfate solution consists of spheri-... 

For flow of some kind of surfactant solutions (Habon G solutions at concentration 530 and 1,060 ppm) in the tube of d = 1.07 mm in the range of Reynolds number based on solvent viscosity Re = 10-450, the increase of pressure drop in adiabatic and diabatic conditions was observed compared to that of pure water. 

Albert Einstein derived a simple equation for the viscosity of a solution of spherical particles, and from this result it is obvious that if we could make the polymer in small colloidal-sized balls, then the solution would be much less viscous. Also, if we could use surfactants to stabilize (e.g. by charging) the polymer particles in water, then there would be no need for organic solvents. Both these conditions are neatly obtained in the emulsion polymerization process, which is schematically explained in Figure 5.3. A polymer latex is produced by this process and can contain up to 50% polymer in the form of 0.1-0.5 im size spherical particles in water. A typical starting composition is ... 

In a previous publication ( ), results were presented on the micellar properties of binary mixtures of surfactant solutions consisting of alkyldimethylamine oxide (C12 to Cig alkyl chains) and sodium dodecyl sulfate. It was reported that upon mixing, striking alteration in physical properties was observed, most notably in the viscosity, surface tension, and bulk pH values. These changes were attributed to 1) formation of elongated structures, 2) protonation of amine oxide molecules, and 3) adsorption of hydronium ions on the mixed micelle surface. In addition, possible solubilisation of a less soluble 1 1 complex, form between the protonated amine oxide and the long chain sulfate was also considered. 

In the presence of sodium tosylate (NaTos), both the rate constant kexp and the viscosity of the solution show maxima at the same electrolyte concentration. The dramatic variation in 17 shown in Figure 8.10a suggests that the sodium tosylate alters the shape of the micelles, first producing rodlike structures that subsequently break up into more compact structures. The complicated phase diagrams of surfactants make this a plausible explanation. Effects such as this clearly complicate the picture not only of inhibition, but also of micellar catalysis in general. 

CMCs in the absence of added electrolyte may be greatly influenced by electrovis-cous effects marked decreases in intrinsic viscosity on electrolyte addition have been observed in many cases36). Peculiar and highly interesting rheological properties of surfactant solutions include observations of strongly non-Newtonian behavior as well as of viscoelasticity these are yet incompletely understood. 

As to the viscosity of aqueous solutions of nonionic surfactants, in general, gel formation tendency is very important. Table V and Figure 5 show differences in viscosity of aqueous solutions and gel ranges for various nonionics. Gel ranges of SAE are remarkably narrow compared with those of PAE and NPE(Table V). 

Due to the relatively high viscosity of surfactant vesicle and microemulsion systems (refer to data on DODAB and CTAB/50J BuOH in Table X), their use in HPLC will be limited since lower flow rates would be required which would lengthen the required time for a separation. Additionally, most surfactant vesicular (112) as well as some micellar solutions are optically opaque which limits the wavelength range available for spectroscopic detection unless a postcolumn dilution step is employed (219). 

In Figure 8, the reduced viscosity of aqueous solutions of the monomeric cationic surfactant is... 

Table I shows various surface and microscopic properties such as surface tension, surface viscosity, foaminess (i.e. foam volume generated in a given time) and bubble size in foams of the surfactant solutions as a function of chain length compatibility. The results indicate that a minimum in surface tension, a maximum in surface viscosity, a maximum in foaminess and a minimum in bubble size were observed when both the components of the mixed surfactant system have the same chain length. These results clearly show that the molecular packing at air-water interface influences surface properties of the surfactant solutions, which can influence microscopic characteristics of foams. The effect of chain length compatibility on microscopic and surface properties of surfactant solutions can be explained as reported in the previous section.

It has often been stated that DR of surfactant solutions is related to their rheological properties. A rise in shear viscosity at a critical shear rate, caused by a shear-induced structure (SIS), viscoelasticity (nonzero first normal stress difference, quick recoil, and stress overshoot), and high extensional viscosity/shear viscosity ratios ( 100) are rheological properties found in many DR surfactant solutions. After reviewing the rheological behavior of many DR surfactant solutions, Qi and Zakin concluded that SIS and viscoelasticity are not always observed in DR surfactant solutions while high extensional/shear viscosity ratios may be a requirement for surfactant solutions to be DR. ... 

In sufficiently dilute aqueous solutions surfactants are present as monomeric particles or ions. Above critical micellization concentration CMC, monomers are in equilibrium with micelles. In this chapter the term micelle is used to denote spherical aggregates, each containing a few dozens of monomeric units, whose structure is illustrated in Fig. 4.64. The CMC of common surfactants are on the order of 10 " -10 mol dm . The CMC is not sharply defined and different methods (e.g. breakpoints in the curves expressing the conductivity, surface tension, viscosity and turbidity of surfactant solutions as the function of concentration) lead to somewhat different values. Moreover, CMC depends on the experimental conditions (temperature, presence of other solutes), thus the CMC relevant for the expierimental system of interest is not necessarily readily available from the literature. For example, the CMC is depressed in the presence of inert electrolytes and in the presence of apolar solutes, and it increases when the temperature increases. These shifts in the CMC reflect the effect of cosolutes on the activity of monomer species in surfactant solution, and consequently the factors affecting the CMC (e.g. salinity) affect also the surfactant adsorption. 

The grid blocks used are 100 x 1 x 1, which is a ID model, and the length is 0.75 ft. Some of the reservoir and fluid properties and some of the surfactant data are listed in Table 8.1. The viscosity of polymer solutions at different concentrations is presented in Figure 8.5. The polymer adsorption data are shown in Figure 8.6. The microemulsion viscosity is shown in Figure 8.7, and the capillary desaturation curves are shown in Figure 8.8. 

At the end of polymer drive—cumulative 0.33 PV injection (4807 m ), including surfactant injection—the producers started to respond. The water cut decreased from 99% before the test to 87%, and the oil rate increased from 0.2 to 1.9 t/d at the peak rate. However, the response lasted only 90 days. In this pilot, the viscosities of micellar solution and polymer solution were 15.7 mPa-s and 14 mPa s, respectively, about twice the oil viscosity. A good mobility ratio might be the main reason for the positive response. 

Below, in Sections 5.2 and 5.3, we consider effects related to the surface tension of surfactant solution and capillarity. In Section 5.4 we present a review of the surface forces due to intermo-lecular interactions. In Section 5.5 we describe the hydrodynamic interparticle forces originating from the effects of bulk and surface viscosity and related to surfactant diffusion. Section 5.6 is devoted to the kinetics of coagulation in dispersions. Section 5.7 regards foams containing oil drops and solid particulates in relation to the antifoaming mechanisms and the exhaustion of antifoams. Finally, Sections 5.8 and 5.9 address the electrokinetic and optical properties of dispersions. 

U.S. 4,256,611 (1981) Egan et al. (Sherex Chemical) Ethylene oxide adduct of partial glycerol esters of detergent-grade fatty acid and certain anionic surfactants Low eye and skin irritation adjust viscosity of aqueous solutions... 

Another problem that the applications chemist may have to contend with is that the perfume may cause shampoo viscosity to decrease or, more often, increase when added to the unfragranced base. If this is a small change, it can be accommodated by varying the level of thickener. However, if dealing with a client s fully formulated base, this may not be an easy option. In such cases, the perfume formulation needs to be screened for ingredients that are known to affect the viscosity of surfactant systems, such as dipropylene glycol or alcohols, e.g. citro-nellol, which often causes a decrease, and diethyl phthalate, isopropyl myristate or terpenes, which can thicken such solutions quite dramatically. 

Liquid crystal structures are important not only in the viscosity modification of surfactant solutions, but also in the stabilization of foams and emulsions, in detergency, in lubrication (Boschkova, 2002), and in other applications. 

Figure 6a. The effect of anionic surfactants used in latex synthesis on the viscosity of 2% solution of HEUR 270. Key A, ammonium salt of nonylphenol ethoxylate average 20 oxyethylene units) sulfate O, ammonium salt of nonylphenol ethoxylate average 9 oxyethylene units) sulfate.

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