Stability of surfactants

The process of adsorption of polyelectrolytes on solid surfaces has been intensively studied because of its importance in technology, including steric stabilization of colloid particles [3,4]. This process has attracted increasing attention because of the recently developed, sophisticated use of polyelectrolyte adsorption alternate layer-by-layer adsorption [7] and stabilization of surfactant monolayers at the air-water interface [26], Surface forces measurement has been performed to study the adsorption process of a negatively charged polymer, poly(styrene sulfonate) (PSS), on a cationic monolayer of fluorocarbon ammonium amphiphilic 1 (Fig. 7) [27],... 

Stability of surfactants in a water matrix, even using different preservation agents, is poor and serious, quantitative and qualitative changes in sample integrity occur if the storage exceeds 7 days. The most suitable preservation additive is formaldehyde (minimum 3%) for non-ionic surfactants and LAS, and acidification to pH < 3 for benzene and naphthalene sulphonates. However, storage for longer than 7 days is not recommended. 

B.P. Binks and S.O. Lumsdon Influence of Particle Wettability on the Type and Stability of Surfactant-Free Emulsions. Langmuir 16, 8622 (2000). 

R.M. Pashley Effect of Degassing on the Eormation and Stability of Surfactant-Free Emulsions and Eine Teflon Dispersions. J. Phys. Chem. B 107, 1714 (2003). 

N. Maeda, K.J. Rosenberg, J.N. Israelachvfli, and R.M. Pashley Eurther Studies on the Effect of Degassing on the Dispersion and Stability of Surfactant Eree Emiflsions. Langmuir 20, 3129 (2004). 

B. P. Binks and S. O. Lumsdon, Influence of particle wettability on the type and stability of surfactant-free emulsions, Langmuir 16, 8622-8631 (2000). 

To approach physical stability problems of suspensions, effectiveness and stability of surfactants as well as salt concentrations must be checked with accelerated aging. In addition, unit operations affecting particle size distribution, surface area, and surfactant effectiveness should be approached, taking into account that different types of distributions, for instance, volume or number weighted, give a different average diameter for an equal sample [43],... 

Thermal Stability. The thermal stability of surfactants has been investigated in a number of studies (1—5). Surfactants with sulfate moieties decompose rapidly at temperatures above 100 °C, and surfactants... 

R. M. Pashley, Effect of degassing on the formation and stability of surfactant-free emulsions and fine teflon dispersions, J. Phys. Chem. B, 2003, 107, 1714—1720. 

In order to emphasize the role of the inter facial films and to highlight the most recent viewpoints on the stability of microemulsions, sponge phases, and dilute lamellar phases, some of the experimental facts about phase behavior of microemulsion systems containing alcohol are reviewed in this chapter. The systems investigated consist of water, oil, alcohol, and sodium dodecylsulfate (SDS). In the next section, the theoretical aspects of the stability of surfactant phases are briefly discussed. Then in Secs. Ill and IV the effects of varying alcohol and oil chain lengths and the addition of a water-soluble polymer are examined. The examination of multiphase regions provides the location of lines of critical points or critical endpoints. This chapter also deals with the study of several physical properties in the vicinity of critical points. 

Maeda, N., Rosenberg, K.J., Israelachvili, J.N., Pashley, R.M. Further studies on the effect of degassing on the dispersion and stability of surfactant-free emulsions. Langmuir 20, 3129-3137 (2004)... 

Thermal Stability of Surfactants for Reservoir Applications., Int. Symp. on Oil Field and Geothermal Chemistry, Houston, Texas, January 22-24, pp. 61-70,... 

Gradients in surface (or interfacial) tension can accelerate the spreading of fluids, enhance the stability of surfactant-laden films of liquid, emulsions, and foams, and increase rates of mass transport across interfaces. The motion of fluid driven by a gradient in surface tension is referred to as a Marangoni flow . We have demonstrated that electrochemical reduction of IF to IF at an electrode that... 

Surfactants may spend long periods of time being transported in the reservoir before interacting to alter the wettability of pore surfaces. The surfactant must maintain its chemical structure and interfacial properties during that time. The long term stability of surfactants at elevated temperatures in an appropriate brine can be monitored in the laboratory from cloud point and interfacial tension measurements [63]. 

Palmer, H. J., and Berg, J. C. (1972). Hydrodynamic stability of surfactant solutions heated from below. J. Fluid Mech. 51 (2) 385-402. 

One way to improve the thermal stability of surfactant molecules is the introduction of aromatic rings into the structure. For example, ammonium 4-(4-adamantylphenoxy)-l-butanamine (APB) salts exhibit higher thermal stability than allyltriphenylphosphonium chloride (APP) (Figure 3.4, Table 3.1). It has been reported that PS nanocomposites prepared by emulsion polymerization, using ammonium surfactants, exhibit exfoliated structures. The PS in such nanocomposites has higher values of Tg and thermal decomposition temperature than are observed for virgin PS [25]. 

In this chapter we wish to explore not only the influence of micelles on reaction rates and the course of reactions, both chemical and photochemical, but also the stability of surfactants themselves and how aggregation can affect their stability. The chemical modification of surface-active agents and attempts to polymerize surfactant micelles will also be covered. The literature on reactivity in micellar systems has grown enormously since 1968 when an account of the pharmaceutical aspects was given in the first edition of this book [1], to the extent that a book has been devoted to the subject reviewing and collating the data in the literature prior to mid-1974 [2]. Here we can probably only hope to extract some of the salient features of the subject, and could certainly not claim to be comprehensive. The reference list, however, contains several reviews which should be consulted for more detailed treatments. The analytical consequences of solubilization of chromophoric species and change in the apparent dissociation constants of compounds in the presence of surfactants is also discussed at the end of the chapter. 

Many of the investigations carried out on mechanisms of catalysis and inhibition in surfactant systems have employed model compounds. Such is the observed specificity of reactions that whatever understanding is gained from the work there can be little confidence in extrapolation of the results to complicated drug structures. This section of the chapter surveys some of the work which has been carried out with pharmaceuticals. A later section will consider the stability of surfactant molecules themselves. 

Another important property of amine oxides is their resistance to oxidation, which makes them suitable for use in foaming bleaches. The bleach stability of surfactants was examined using the formulation in Table 63 and monitoring hypochlorite concentration for 6 months. The initial available chlorine was 2.0%. The test was run until the available chlorine dropped down to 1% or to 180 days, whichever came first. The results, listed in Table 64, show that amine oxides are one of the best surfactants for use with chlorine bleaches. 

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