Distribution, nonionic surfactants

Brooks and Richmond - developed a simple surfactant partitioning model that can be applied to isothermal transitional inversions. The linearity and gradient variation of transitional inversion lines in systems containing distributed nonionic surfactant was also explained. The derived model used mixed surfactant theory to predict the slope of the SAD = 0 line with surfactant concentration, for transitional inversion induced by varying the amount of a homogeneous lipophilic and a homogeneous hydrophilic surfactant in an oil-water system. 

The sulfonate content was determined either by the well-known technique of two-phase titration with hyamine or by liquid chromatography (HPCL). Nonionic surfactants were analyzed by HPLC (16) in the reverse or normal phase mode depending on whether the aim was to determine their content in effluents or to compare their ethylene oxide distribution. 

In the same way, after transit through a porous medium, non appreciable change was found in the ethylene oxide distribution of nonionic surfactants used as a cosurfactant or desorbent. 

Surfactants are separated according to adsorption or partitioning differences with a polar stationary phase in NPLC. This retention of the polar surfactant moiety allows for the separation of the ethylene oxide distribution. Of all the NPLC packings that have been utilized to separate nonionic surfactants, the aminopropyl-bonded stationary phases have been shown to give the best resolution (Jandera et al., 1990). The separation of the octylphenol ethoxylate oligomers on an amino silica column is shown in Fig. 18.4. Similar to the capabilities of CE for ionic surfactants, the ethylene oxide distribution can be quantitatively determined by NPLC if identity and response factors for each oligomer are known. 

Rgure 1.27. Emulsion obtained by shearing a premixed emulsion in presence of a nonadsorbing polymer. System composition sodium alginate (nonadsorbing polymer) 4 wt%, nonionic surfactant (NP7) 3 wt%, oil fraction = 30 wt%. (a) Size distribution, (b) microscopic image. (Adapted from [137].)... 

Commercial nonionic surfactants are mixtures of multiple species with different degrees of ethoxylation and typically with some distribution in hy-... 

We commence with the adsorption of nonionic surfactants, which does not require the consideration of the effect of the electrical double layer on adsorption. The equilibrium distribution of the surfactant molecules and the solvent between the bulk solution (b) and at the surface (s) is determined by the respective chemical potentials. The chemical potential /zf of each component i in the surface layer can be expressed in terms of partial molar fraction, xf, partial molar area a>i, and surface tension y by the Butler equation as [14]... 

In another communication using w/o microemulsions containing a nonionic surfactant, it is shown that TEOS hydrolysis and siUca-particle growth occur at the same rate, indicating the growth of siUca particles is rate-controlled by the hydrolysis of TEOS [54], The rate of TEOS hydrolysis also depends on the surfactant concentration, which controls the molecular contact between hydroxyl ions and TEOS in solution. Because of the reaction-controlled growth mechanism, the silica-particle size distribution remains virtually same over the growth period. 

As the temperature of dilute aqueous solutions containing ethoxylated nonionic surfactants is increased, the solutions may turn cloudy at a certain temperature, called the cloud point. At or above the cloud point, the cloudy solution may separate into two isotropic phases, one concentrated in surfactant (coacervate phase) and the other containing a low concentration of surfactant (dilute phase). As an example of the importance of this phenomena, detergency is sometimes optimum just below the cloud point, but a reduction in the washing effect can occur above the cloud point (95). However, the phase separation can improve acidizing operations in oil reservoirs (96) For surfactant mixtures, of particular interest is the effect of mixture composition on the cloud point and the distribution of components between the two phases above the cloud point. 

The equilibrium in these systems above the cloud point then involves monomer-micelle equilibrium in the dilute phase and monomer in the dilute phase in equilibrium with the coacervate phase. Prediction o-f the distribution of surfactant component between phases involves modeling of both of these equilibrium processes (98). It should be kept in mind that the region under discussion here involves only a small fraction of the total phase space in the nonionic surfactant—water system (105). Other compositions may involve more than two equilibrium phases, liquid crystals, or other structures. As the temperature or surfactant composition or concentration is varied, these regions may be encroached upon, something that the surfactant technologist must be wary of when working with nonionic surfactant systems. 

Anionic surfactant Sodium dodecyl sulfate (SDS, C] 2 25 3 supplied by Nihon Surfactant Industries Co., Ltd Tokyo, Japan. It was extracted with ether and recrystallized from ethanol. The purity was ascertained by surface tension measurement. Nonionic surfactant Alkyl poly(oxyethylene) ether (CjjPOEjj, CmH2nhPlO(CH2CH20)2oH, m=12, 14, 16, and 18 Ci6H330(CH2CH20) H, n=10, 20, 30, and 40) were supplied by Nihon Surfactant Industries Co., Ltd. These have a narrow molecular weight distribution. 

The third factor determining the distribution of surfactant between the solution and the surface phase is represented by the third term from the right in Equation 17. It involves the interaction between the two surfactant species, i.e. Xl2 Analysis of the cmc of mixed surfactant systems (6-7) reveals that there is normally a net attraction when anionic and nonionic surfactants are mixed. This corresponds to a negative Xi2 suggested explanation is that the... 

Marszall (1988) studied the effect of electrolytes on the cloud point of mixed ionic-nonionic surfactant solutions such as SDS and Triton X-100. It was found that the cloud point of the mixed micellar solutions is drastically lowered by a variety of electrolytes at considerably lower concentrations than those affecting the cloud point of nonionic surfactants used alone. The results indicate that the factors affecting the cloud point phenomena of mixed surfactants at very low concentrations of ionic surfactants and electrolytes are primarily electrostatic in nature. The change in the original charge distribution of mixed micelles at a Lxed SDS-Triton X-100 ratio (one molecule per micelle), as indicated by the cloud point measurements as a function of electrolyte concentration, depends mostly on the valency number of the cations (counterions) and to some extent on the kind of the anion (co-ion) and is independent of the type of monovalent cation. 

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