Surfactant and polymer adsorption

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]. 

Alkali compounds are used in the Surtek process to reduce the interfacial tension between the oil phase and the aqueous phase. In addition, an alkaline agent neutralizes rock and clay surfaces and reduces the amount of exchangeable calcium and magnesium ions from the soil surface. Both of these functions reduce surfactant and polymer adsorption into the soil matrix. 

In the various sections of this chapter, I will briefly describe the major characteristics of FT-IR, and then relate the importance of these characteristics to physiochemical studies of colloids and interfaces. This book is divided into two major areas studies of "bulk" colloidal aggregates such as micelles, surfactant gels and bilayers and studies of interfacial phenomena such as surfactant and polymer adsorption at the solid-liquid interface. This review will follow the same organization. A separate overview chapter addresses the details of the study of interfaces via the attenuated total reflection (ATR) and grazing angle reflection techniques. 

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. 

Almost all chemical EOR applications have been in sandstone reservoirs, except a few stimulation projects and a few that have not been published have been in carbonate reservoirs. One reason for fewer applications in carbonate reservoirs is that anionic surfactants have high adsorption in carbonates. Another reason is that anhydrite often exists in carbonates, which causes precipitation and high alkaline consumption. Clays also cause high surfactant and polymer adsorption and high alkaline consumption. Therefore, clay contents must be low for a chemical EOR application to be effective. 

In this chapter specific theories and experimental set-ups for interfacial relaxation studies of soluble adsorption layers are presented. A general discussion of relaxation processes, in bulk and interfacial phases, was given in Chapter 3. After a short introduction, in which the important role of mechanical properties of adsorption layers and the exchange of matter for practical applications are discussed, the main differences between adsorption kinetics studies and relaxation investigations are explained. Then, general theories of exchange of matter and specific theories for different experimental techniques are presented. Finally, experimental setups, based on harmonic and transient interfacial area deformations, are described and results for surfactant and polymer adsorption layers discussed. 

Surface properties can be adjusted by the adsorption of surfactants and polymers. Adsorption itself can essentially be considered to be preferential partitioning of the adsorbate into the into the interfacial region. It is the result of one or more contributing forces arising from electrostatic attraction, chemical reaction, hydrogen bonding, hydro-phobic interactions, and solvation effects. 

Since surfactant and polymer adsorption processes are significantly different, the two subjects will be treated differently - surfactant adsorption is relatively simpler than polymer adsorption. This is because surfactants consist of a small number of units and they mostly are reversibly adsorbed, allowing one to apply thermodynamic treatments. In this case, it is possible to describe the adsorption in terms of the various interaction parameters, namely chain-surface, chain-solvent and surface-solvent. Moreover, the conformation of the surfactant molecules at the interface can be deduced from these simple interactions parameters. In contrast, polymer adsorption is fairly complicated. In addition to the usual adsorption considerations described above, one of the principle problems to be resolved is the conformation of the polymer molecule at the surface. This can be acquired in various ways depending on the number of segments and chain flexibility. This requires the application of statistical thermodynamic methods. 

All three investigations require several sophisticated techniques, such as zeta potential measurements, surfactant and polymer adsorption and their conformation at the solid/liquid interface, measurement of the rate of flocculation and crystal growth, and several rheological measurements. 

For the full assessment of the properties of suspension concentrates, three main types of investigations are needed (i) the fundamental investigation of the system at a molecular level (ii) investigations into the state of the suspension on standing (iii) bulk properties of the suspension. All these investigations require a number of sophisticated techniques such as zeta potential measurements, surfactant and polymer adsorption and their conformation at the solid/liquid interface, measurement of the rate of flocculation and crystal growth, and several rheological measurements. Apart... 

For convenience, 1 list the topics of colloid and interface science under two main headings disperse systems and interfacial phenomena. This subdivision does not imply any separation for the following reasons. All disperse systems involve an interface. Many interfacial phenomena are precursors for the formation of disperse systems, e.g. nucleation and growth, emulsiflcation, etc. The main objective of Vol. 1 is to cover the following topics the basic principles involved in interfacial phenomena as well as the formation of colloidal dispersions and their stabilization surfactants and polymer adsorption at various interfaces and interfacial phenomena in wetting, spreading euid adhesion the subject of particle deposition and adhesion is also discussed in detail in Vol. 1. 

H.S. Hanna and P. Somasundaran, "Physico-Chemical Aspects of Adsorption at Solid/Liquid Interfaces, Part II. Berea Sandstond/Mahogony Sulfonate System", in Improved Oil Recovery by Surfactants and Polymer Flooding, D.O. Shah and R.S. Schecter, eds.. Academic Press, 1977, p. 253-274. 

Malmberg, E.W. Smith, L. The Adsorption Losses of Surfactants in Tertiary Recovery Systems in Porous Media in Improved Oil Recovery by Surfactant and Polymer Flooding, Shah, D.O. Schechter, R.S. (Eds.), Academic Press New York, 1977, pp. 275-292. 

Examples of the adsorption of dmgs and excipients on to solid surfaces are found in many aspects of dmg formulation, some of which, for example the adsorption of surfactants and polymers in the stabilisation of suspensions, are considered elsewhere in this book (see section 7.4). An interesting approach to the improvement of the dissolution rate of poorly water-soluble dmgs is to adsorb very small amounts of surfactant on to the drug surface. For example, the adsorption of Plutonic F127 onto the surface of the hydro-phobic dmg phenylbutazone significantly increased its dissolution rate when compared with untreated material."... 

The adsorption or incorporation of molecules, such as surfactants and polymers, can create a steric repulsion that prevents aggregation [288-290]. This can also increase suspension stability, important for metered-dose inhaler formulations [291]. Lung surfactant coating on the surface of poly(lactic-co-glycolic) acid microparticles has been shown to dramatically improve dry powder aerosol performance by reducing particle-particle interactions [134,292],... 

The preceding four types of consumption mnst be determined experimentally in the laboratory and upscaled to field scales. The experimental conditions should be as close to the field conditions as possible. Field oil and water samples can be obtained, and experiments shonld be condncted at the held temperature. Ideally, reservoir rocks should be used. In practice, we may not be able to conduct all the necessary experiments becanse of the cost, available resources, and limited time. An approximation mnst be made to estimate the consumption for each type. For example, the consnmption for alkali reaction with crude oil can be estimated from Eq. 10.12, assnming all the acidic components are consumed to react with the alkali. The alkali consumption ACo in meq/mL is the same as the soap generated. ACo is generally a small fraction of the total consumption. Because these consumptions involve complex chemical reactions, efforts have been made to collect some published experimental data and were presented earlier. A general rule is 0.05 to 2% alkali concentration and 0.1 to 0.23 PV injection volnme. Note that alkali addition in an ASP system can rednce snrfactant and polymer adsorption. However, addition of snrfactant and/or polymer does not affect alkali consumption (Li, 2007). This is probably because the alkali molecules are smaller than the surfactant or polymer molecules, thus the existence of snrfactant and polymer molecnles will not affect the adsorption of alkali molecnles, nor will their existence affect alkahne reactions. 

One natural core was used to compare the performance of waterflood (W), AP flood, and ASP flood. The recovery factors for W, AP, and ASP were 50%, 69.7%, and 86.4%, respectively. These core flood tests were history matched, and the history-matched model was extended to a real field model including alkaline consumption and chemical adsorption mechanisms. A layered heterogeneous model was set up by taking into account the pilot geological characteristics. The predicted performance is shown in Table 11.3. In the table, Ca, Cs, and Cp denote alkaline, surfactant, and polymer concentrations, respectively. After the designed PV of chemical slug was injected, water was injected until almost no oil was produced. The total injection PV for each case is shown in the table as well. The cost is the chemical cost per barrel of incremental oil produced. An exchange rate of 7 Chinese yuan per U.S. dollar was used. From... 

The chemical formnla in this pilot test was 1.25% NaaCOs + 0.3% B-lOO + 1200 ppm 1275A blended in fresh water. Table 13.10 shows the IFT values at different alkahne and surfactant concentrations. The table also shows that ultralow IFT of 10 mN/m was reached within a large range of concentrations, particularly near the designed injection concentrations. The chemical adsorption or consumption for alkah, surfactant, and polymer were 1.065,0.455,0.169 (mg/mL PV), respectively. The residual resistance factor in this test was 2.0695. The injection scheme was 0.32 PV ASP solution, then 600 mg/L polymer buffer solution, followed by water until the water cut reached 98%. 

Polymers are also essential for the stabilisation of nonaqueous dispersions, since in this case electrostatic stabilisation is not possible (due to the low dielectric constant of the medium). In order to understand the role of nonionic surfactants and polymers in dispersion stability, it is essential to consider the adsorption and conformation of the surfactant and macromolecule at the solid/liquid interface (this point was discussed in detail in Chapters 5 and 6). With nonionic surfactants of the alcohol ethoxylate-type (which may be represented as A-B stmctures), the hydrophobic chain B (the alkyl group) becomes adsorbed onto the hydrophobic particle or droplet surface so as to leave the strongly hydrated poly(ethylene oxide) (PEO) chain A dangling in solution The latter provides not only the steric repulsion but also a hydrodynamic thickness 5 that is determined by the number of ethylene oxide (EO) units present. The polymeric surfactants used for steric stabilisation are mostly of the A-B-A type, with the hydrophobic B chain [e.g., poly (propylene oxide)] forming the anchor as a result of its being strongly adsorbed onto the hydrophobic particle or oil droplet The A chains consist of hydrophilic components (e.g., EO groups), and these provide the effective steric repulsion. 

These forces and hence the stability of the dispersions can be altered/controlled by the adsorption of ions, surfactants, or polymers at the solid-liquid interface. Adsorption of surfactants and polymers at the solid-liquid interface depends on the nature of the surfactant or polymer, the solvent, and the substrate. Ionic surfactants adsorbing on oppositely charged surfaces exhibit a typical four-region isotherm. Such adsorption can alter the dispersion stability mainly by changing the double layer interaction, which depends on the extent of adsorption. Thus, it is seen that alumina suspensions are destabilized by the adsorption of SDS when the zeta potential is reduced to zero. At higher concentrations, bilayered surfactant adsorption can occur with changes in wettability and flocculation of the particles by altering the hydrophobic interactions. 

The preflush (or preliminary injection) is a slug applied to prepare the reservoir to help in protecting the surfactants and polymers against salinity effects and adsorption on the... 

Understanding of the structure of the adsorbed surfactant and polymer layers at a molecular level is helpful for improving various interfacial processes by manipulating the adsorbed layers for optimum configurational characteristics. Until recently, methods of surface characterization were limited to the measurement of macroscopic properties like adsorption density, zeta-potential and wettability. Such studies, while being helpful to provide an insight into the mechanisms, could not yield any direct information on the nanoscopic characteristics of the adsorbed species. Recently, a number of spectroscopic techniques such as fluorescence, electron spin resonance, infrared and Raman have been successfully applied to probe the microstructure of the adsorbed layers of surfactants and polymers at mineral-solution interfaces. 

Qualitative and quantitative models of adsorption kinetics of surfactants and polymers are described in this chapter. A comprehensive presentation of the most developed physical model, the difRision-controlled adsorption and the desorption model, is given and different methods of solving the resulting differential equations are discussed (Miller Kretzschmar 1991). A direct numerical integration enables us to consider any type of adsorption isotherm relating the surfactant bulk concentration with the adsorbed amount at the interface. 

A new insight into the dynamic processes in the bulk and at the surface of surfactant solutions can be seen in molecular dynamics simulations. Only now are computers sufficiently powerful that such simulations can be performed without too many simplifications. The state of the art of molecular dynamics was recently summarised by van Os Karabomi (1993), showing that complex processes such as micelle formation (Karabomi O Connell 1993), emulsion formation or solubilisation processes (Smit et al. 1993) can be simulated. Future improvements of computers and algorithms will provide a deep insight into even more complex processes connected with dynamics of interfacial phenomena, such as adsorption layer stracture and formation, effects of molecular interfacial and bulk interactions in mixed systems of surfactants and polymers. 

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