Studies of Surfactant Solutions

6 Never pipette a solution or a liquid by mouth. Use the appropriate safety pipettes and keep these in a beaker. 

7 A tray, lined with disposable paper, should be used for all manipulations, e.g. transfer of solutions, dilutions, etc. 

9 Keep all contaminated glassware on a tray so that each flask, pipette, etc. can be accounted for at the end of the experiment. 

10 Report any accidents or spillage immediately, ensuring that all other workers are aware of the contaminated area. 

11 Before leaving the laboratory, wash your hands thoroughly and monitor them in the hand monitor. 

---

Over the past few decades there has been an increase in the research tools for fundamental rheology studies of surfactant solutions and commercial detergent formulations. The coupling of rheometers with other methods has broadened the range of studies that can be completed, leading to a better understanding of solution properties, self-assembled mesophases, multiple-component dispersions, and gels. 

Measurements of the equilibrium surface tension in a broad concentration range above and below the CMC is one of the most conventional methods in the studies of surfactant solutions. The first derivative of the concentration dependence of the surface tension jumps at a certain... 

The results of studies of surfactant solution properties were classically interpreted in terms of a spherical association of surfactant molecules the micelle. The structure was assumed to be an aggregate of from 50-100 molecules with a radius approximately equal to the length of the hydrocarbon chain of the surfactant Fig. 15.6). The interior of the micelle was described as being essentially hydrocarbon in nature, while the surface consisted of a layer or shell of the head groups and associated counterions, solvent molecules, and similar items. 

As mentioned, CPP has a special role in the studies of surfactant solutions, among other reasons due to its connection with the micellar structure. One of the most well-known surfactants, SDS, forms often (semi)... 

Using the drop and bubble profile analysis tensiometer PAT-1 (SINTERFACE Technologies, Berlin, Germany) it is possible to perform dilational rheology studies of surfactant solutions at low frequencies. 

Although the study of surfactant solution properties throughout the complete concentration range is of obvious theoretical and occasional practical importance, no attempt is made to cover in detail those phases more stmctured than the simplest aggregates of surfactants in dilute solution. For more information on surfactant phase diagrams, the reader is referred to the excellent works of Laughlin cited in the Bibliography for this chapter. 

It was determined, for example, that the surface tension of water relaxes to its equilibrium value with a relaxation time of 0.6 msec [104]. The oscillating jet method has been useful in studying the surface tension of surfactant solutions. Figure 11-21 illustrates the usual observation that at small times the jet appears to have the surface tension of pure water. The slowness in attaining the equilibrium value may partly be due to the times required for surfactant to diffuse to the surface and partly due to chemical rate processes at the interface. See Ref. 105 for similar studies with heptanoic acid and Ref. 106 for some anomalous effects. 

A recent design of the maximum bubble pressure instrument for measurement of dynamic surface tension allows resolution in the millisecond time frame [119, 120]. This was accomplished by increasing the system volume relative to that of the bubble and by using electric and acoustic sensors to track the bubble formation frequency. Miller and co-workers also assessed the hydrodynamic effects arising at short bubble formation times with experiments on very viscous liquids [121]. They proposed a correction procedure to improve reliability at short times. This technique is applicable to the study of surfactant and polymer adsorption from solution [101, 120]. 

TITRATIONS FOR COMPARISON OF METHODS. The automated photometric and turbidimetric methods were compared using 30 cm3 samples of surfactant solution containing a nominal 20 mol SDBS to give an equivalence volume of 5 cm3. The effect of salinity on the titrations was studied using samples prepared containing sodium chloride concentrations of 0.0, 0.14, 0.70 and 1.46 wt%. The influence of the choice of filter (580 or 620 nm) was also investigated. 

Although silicone oils by themselves or hydrophobic particles (e.g., specially treated silica) are effective antifoams, combinations of silicone oils with hydrophobic silica particles are most effective and commonly used. The mechanism of film destruction has been studied with the use of surface and interfacial tensions, measurements, contact angles, oil-spreading rates, and globule-entering characteristics for PDMS-based antifoams in a variety of surfactant solutions.490 A very recent study of the effect of surfactant composition and structure on foam-control performance has been reported.380 The science and technology of silicone antifoams have recently been reviewed.491... 

A linear correlation is obtained between bitumen extraction with the paddle mill and the adhesion tension against water saturated pyrophyllite. That the degree of water saturation of the pyrophyllite is important in explaining the difference between the 2 extraction processes indicates that it will be necessary to study each process in terms of the relevant adhesion tensions. These results demonstrate that adhesion tension is the most important parameter found to date in determining the degree of separation in the presence of surfactants. Measurements of adhesion tension between surfactant solutions and minerals similar to those found in tar sand may be of considerable value in studies of surfactant utility in both aqueous-surfactant, solvent-aqueous-surfactant and in situ extraction processes. In addition, if appropriate model situations can be developed, measurements of adhesion tension may be useful in upgrading bitumen-water-clay emulsions obtained by a variety of in situ and heavy oil recovery processes. 

Ananthapadmanabhan KP, Goddard ED, Chandar P (1990) A study of the solution, interfacial and wetting properties of silicone surfactants. Colloid Surf 44 281-297... 

Smirnova, N. A. 1995. Thermodynamic study of micellar solution-solid surfactant equilibRUrtti Phase Equilibria 110 1-15. 

Sorption is measured by recording sorption isotherms, which themselves are a way to express the amount of surfactant sorbed as function of the concentration of the compound in the solution. The Freundlich isotherm (Equation II) is a general sorption isotherm which describes sorption behavior and often is used in studies of surfactant sorption. KF is the Freundlich sorption coefficient which expresses the affinity of a surfactant for a given solid... 

Approximately 7.9 and 7.6 pore volumes (8.7 L and 8.3 L) of surfactant solution were flushed through Box A and Box B, respectively. The effects of non-equilibrium mass transfer on PCE recovery were assessed through a series of flow interruptions, lasting from 12 to 17 hours. PCE remaining in each box after the surfactant flushing procedure was extracted with isopropanol and analyzed by GC. Total PCE mass balances of greater than 94% PCE was achieved in both box studies. 

The viscosity starts to increase above the CMC and it is well established that the viscosity of a colloidal solution can give information on size and shape of the particles. From studies of the viscosity as a function of micellar concentration, the intrinsic viscosity may be obtained by extrapolation. The intrinsic viscosity depends on a shape factor, and the micelle specific volume and viscosity studies are therefore used to determine micelle shape and hydration. In many cases, these factors appear to be quite constant over a wide concentration range above the CMC. In other cases, such as hexadecyltrimethylammonium bromide (Fig. 2.9), dramatic increases in viscosity are observed at higher concentrations35). Studies of surfactants with low... 

In applying this technique to the study of micellar solutions the intensity versus concentration function is usually extrapolated to obtain the CMC (at constant scattering angle). Since, however, the CMC occurs in apolar surfactant solutions at concentrations where the turbidity is indistinguishable from that of the pure solvent, extrapolation was frequently made to zero concentration. 

In this report we describe novel pressure tuning vibrational spectroscopic techniques that can be used to study aqueous surfactant solutions and discuss in some detail two examples of such studies with micellar solutions of anionic surfactants, one using Fourier transform infrared (FT-IR) and another using Raman spectroscopy. 

In the last 10-15 years, neutron reflectometry has been developed into a powerful technique for the study of surface and interfacial structure, and has been extensively applied to the study of surfactant and polymer adsorption and to determine the structure of a variety of thin films [14, 16]. Neutron reflectivity is particularly powerful in the study of organic systems, in that hydrogen/deu-terium isotopic substitution can be used to manipulate the refractive index distribution without substantially altering the chemistry. Hence, specific components can be made visible or invisible by refractive index matching. This has, for example, been extensively exploited in studying surfactant adsorption at the air-solution interface [17]. In this chapter, we focus on the application of neutron reflectometry to probe surfactant adsorption at the solid-solution interface. 

The scope of the chapter will include an introduction to the technique of neutron reflectometry, and how it is applied to the study of surfactant adsorption at the planar solid-solution interface, to obtain adsorbed amounts and details of the structure of the adsorbed layer. The advantages and limitations of the technique will be put in the context of other complementary surface techniques. Recent results on the adsorption of a range of anionic, cationic and nonionic surfactants, and surfactant mixtures onto hydrophilic, hydrophobic surfaces, and surfaces with specifically tailored functionality will be described. Where applicable, direct comparison with the results from complementary techniques will be made and discussed. 

Much of the early studies of surfactant adsorption at the solid-solution interface were based on classical experimental techniques, such as solution depletion [1, 32], fluorescence spectroscopy [2], and measurements of the differential enthalpy of adsorption [2], Such methods have provided much of the basic initial understanding. However, they provide no direct structural information and are difficult to apply to mixtures [23, 34], However, when combined with other techniques, such as NMR and flow microcalorimetry, they provide some insight into the behaviour of mixtures. This was demonstrated by Thibaut et al. [33] on SDS/C10E5 mixtures adsorbed onto silica and by Colombie et al. [34] on the adsorption of SLS/Triton X-405 mixtures onto polystyrene particles. 

ADSA-P has been employed in various surface tension and contact angle studies, including static (advancing) contact angles [69.70], dynamic (advancing) contact angles at slow motion of the three-phase contact line [4, 71—74], and contact angle kinetics of surfactant solutions [75]. A schematic of the experimental setup for ADSA-P sessile drops is shown in Fig. 6. More details are available elsewhere [66[. 

Two sets, i.e., four experiments, of core flow studies are compared. Sets No. 1 and No. 2 were tertiary miscible and immiscible CO2 floods without mobility control. The same core from each set, after plain CO2 injection, was restored to waterflood residual oil saturation and flooded with 0.05% AEGS 25-12 surfactant in brine. There was almost no difference between the oil saturation distributions in the cores between experiments, with the average Sorw values of 37 1 saturation percent in both sets of experiments. CO2 was injected continuously in all experiments at a nominal rate of 1 ft/day. No attempt was made to preform a foam, or to inject alternate slugs of surfactant solution and CO2. 

Previous studies have shown that foam can be effectively used to mitigate oil bypassing. Foam can be injected into a reservoir, or, preferably, it can be generated in situ. The in situ generation is accomplished by injecting a bank of surfactant solution followed by the injection of the gas. The latter method avoids increased injection pressure that would result from the foam s low mobility in or near the injection well. 

---