Mixed anionic and nonionic

The most common method of stabilizing latex particles is by addition of mixed anionic and nonionic surfactants. The key property of a siufactant is that it possesses chemically dissimilar groups one hydrophobic and one hydrophilic. The hydrophobic group is physically adsorbed onto the polymer latex particle while the hydrophilic portion extends into the aqueous phase. It is the hydrophilic groups that provide the stabilization. 

EMULSION POLYMERISATION OF STYRENE STABILISED BY MIXED ANIONIC AND NONIONIC SURFACTANTS Chem C S Lin S Y Chen L J Wn S C Taiwan,National Institnte of Technology Taiwan,National University... 

Mixed anionic and nonionic surfactant systems have been widely used in industry to manufacture latex products. Anionic surfactants can provide electrostatic repulsion force between two similarly charged electric double layers. By contrast, nonionic surfactants can impart two approaching latex particles... 

Unzueta and Forcada [93] developed a mechanistic model for the emulsion copolymerization of methyl methacrylate and n-butyl acrylate stabilized by mixed anionic and nonionic surfactants, which was verified by the experimental data. This model is based on the mass and population balances of precursor particles and the moments of particle size distribution. It is sensitive to such parameters as the composition of mixed surfactants and the total surfactant concentration. A competitive particle nucleation mechanism is incorporated into the model to successfully simulate the evolution of particle nuclei during polymerization. 

The target HLB can be obtained by using a mixture of anionic surfactant (HLB = 9.4) and nonionic surfactant HLB = 16.7) in the right proportions (1 3.75 based on the formula in Table 3). Such mixing of anionic and nonionic surfactants is expected to lower the individual CMC s and thus an increase of the soil solubilization capacity. The surfactants in the product should be in spherical micelle phase to give a transparent/translucent appearance and small viscosity (Table 6). 

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... 

Others have studied the volumetric changes occurring in mixed micelles of anionic-anionic and nonionic-nonionic surfactants as a determinant of intermolecular interactions and a measure of the thermodynamic ideality of mixing. In particular, Funasaki et al. (1986) have studied the volumetric behavior of mixed micelles of ionic and nonionic surfactants and analyzed their results in terms of regular solution theory. They found that in water, anionic surfactants such as SDS bind to PEG,... 

There are an enormous variety of commercial emulsifiers that are employed in emulsion polymerization. Emulsifiers are generally categorized into four major classes anionic, cationic, nonionic and zwitterionic (amphoteric). The anionic and nonionic emulsifiers are the most widely used. In addition, mixtures of emulsifiers are also often used. Since the effects of the molecular structme and chemical and physical properties of an emulsifier on particle formation are still far from being well understood, numerous experimental investigations on particle formation have been carried out to date with various nonionic emulsifiers [99-102], mixed emulsifiers (ionic and nonionic emulsifiers) [18,103-106] and reactive surfactants [33, 107-110]. Recently, polymeric surfactants have become widely used and studied in emulsion polymerizations [111-116]. A general review of polymeric surfactants was published in 1992 by Piirma [117]. Recently, emulsion polymerization stabilized by nonionic and mixed (ionic and nonionic) emulsifiers was reviewed by Capek [118]. 

Abdul et al. (7) studied the performance of commercially available anionic and nonionic surfactants to clean a sandy soil contaminated with automatic transmission fluid (ATF). Using a batch shaker method, Abdul et al. mixed 5 g of contaminated soil with 100 mL of 0.5% by volume surfactant solution fw min. After the soil settled. 

With many industrial formulations, surfactants of different kinds are mixed together, for example anionics and nonionics. The nonionic surfactant molecules shield the repulsion between the negative head groups in the micelle, and consequently there will be a net interaction between the two types of molecules. Another example is the case when anionic and cationic surfactants are mixed, whereby a very strong interaction will take place between the oppositely charged surfactant molecules. To account for this interaction. Equation (3.25) must be modified by introducing activity coefficients of the surfactants,/j" and/2 in the micelle. 

Use of mixed surfactant films In many cases the used of mixed surfactants (e.g., anionic and nonionic or long chain alcohols) can reduce coalescence as a result of several effects a high Gibbs elasticity high surface viscosity and hindered diffusion of surfactant molecules from the film. 

This section briefly describes the anionic and nonionic surfactants commonly used in commercial HDLD formulations. Cationic surfactants, although used on a large scale, are found predominantly in rinse-added fabric softener products. LAS, alcohol ethoxylates, and alkyl ether sulfates are three of the most widely used surfactants in liquid laundry detergents [44], Recently, various external considerations, such as environmental pressures, have prompted manufacturers to change their surfactant mix to include newer natural-based surfactants [45-47], including alkyl polyglucosides (Henkel) [48],... 

The described mechanisms of detergency are put into practice by using synthetic micelle-forming surfactants, among which the mixtures of anionic and nonionic surfactants (particularly alkylsulfates and oxyethylenated alcohols) make 10 to 40 % of the total detergent formulation. Cationic surfactants (alkylamines) that are also included into synthetic detergent formulations may contribute up to 5% of the total amount of formulation. These substances reveal biocidal action and control micelle formation by forming mixed micelles. 

The order of component addition is important. The mixing of concentrated anionic and nonionic surfactants must be avoided because it produces gels that dissolve very slowly. Typically, a master batch of nonionic surfactant, initiator, and LMA was prepared for use with all the solutions of a series of experiments. This approach ensures that the small concentration components are all at the same concentration. To a portion of this well-mixed master batch was added more nonionic surfactant if necessary, propanamide (if used), water to about 80 g, anionic surfactant, mercaptoethanol, and water to 100 g, with stirring as appropriate. 

The presence of electrolytes increases the adsorption of anionic surfactants at the gas/liquid interface, as already mentioned. This leads to a reduction of the surface tension at an equal solution concentration (5) and to a strong decrease of the cmc (Figure 3.2). This effect can be of the magnitude of several decades in order. Similar to this are the effects of mixtures of surfactants with the same hydrophilic group and different alkyl chain lengths or mixtures of anionic and nonionic surfactants (6). Such mixtures follow the mixing rule (equation (3.1)) in the ideal case, as follows ... 

In contrast to anionics, common nonionic surfactants have appreciable solubility in hydrocarbons. As a result, when mixtures of individual nonionic surfactants are present, as inevitably is the case for commercial products, or when anionic and nonionic surfactants are mixed, diff ntial partitioning occurs and the composition of the surfactant films in the microranulsions formed depends on both the total surfactant concentration and the wateroil ratio. For instance, an increase in surfactant concentration while maintaining a fixed overall ratio of anionic to nonionic surfactant produces a reduced ratio of the two species in the surfactant films. The result is to increase v /a/ and reduce the PIT for the typical case where the nonionic surfactant has the higher value of v /aZ. Methods for relating the PIT or optimal conditions to surfactant concentration and the relative amoimts of oil and water present have been developed (Kunieda and Ishikawa, 1985 Kunieda and Shinoda, 1985). 

When surfactant mixtures of practical interest containing multiple species were used (e.g., commercial nonionic surfactants or mixtures of anionic and nonionic surfactants), a maximum in hydrocarbon removal from polyester/cotton fabric similar to that in Figure 4.32 was again seen. For situations where the surfactant oil ratio in the system is large, the typical case for household washing, the maximum occurred at the PIT of a system for which surfactant composition in the films separating oil and water domains of the microemulsion phase was the same as the initial surfactant composition (Raney and Miller, 1987). This result is reasonable since the small amount of hydrocarbon present can dissolve only a small portion of the total surfactant, leaving the remainder, which has neariy the initial composition, to make up the films. It should be noted that here too the PIT is well above the cloud point temperature of the mixed surfactant solution. 

Liu et al. determined capsaicin and dihydrocapsaicin in C. annuum and related products by CE with a mixed surfactant system [102]. The mixed surfactant systems composed of two or more surfactants have shown unique selectivity because of synergism effect due to mixing of anionic and nonionic surfactants [123]. 

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