Anionic surfactants, polystyrene

In this chapter the introduction of a polymeric anionic surfactant, polystyrene sulfonate, to bring about a marked effect on tbe crystaUinity of ammonium nitrate is discussed and the evidence for microcrystaUine forms of ammonium nitrate induced by polystyrene sulfonate is presented. There are many additives docmnented in the literature that are claimed [1-4], with some evidence, to produce porous ammonium nitrate prill with desirable strength and internal stability. There is, however, very little understanding of these systems, particularly in relation to crystallization. The possible mechanisms of polystyrene sulfonate in relation to its water association as weU as (hying properties in (aystallizing ammonium nitrate are discussed in the following sections. 

CE has been used for the analysis of anionic surfactants [946,947] and can be considered as complementary to HPLC for the analysis of cationic surfactants with advantages of minimal solvent consumption, higher efficiency, easy cleaning and inexpensive replacement of columns and the ability of fast method development by changing the electrolyte composition. Also the separation of polystyrene sulfonates with polymeric additives by CE has been reported [948]. Moreover, CE has also been used for the analysis of polymeric water treatment additives, such as acrylic acid copolymer flocculants, phosphonates, low-MW acids and inorganic anions. The technique provides for analyst time-savings and has lower detection limits and improved quantification for determination of anionic polymers, compared to HPLC. 

Recent investigations have shown that the behavior and interactions of surfactants in a polyvinyl acetate latex are quite different and complex compared to that in a polystyrene latex (1, 2). Surfactant adsorption at the fairly polar vinyl acetate latex surface is generally weak (3,4) and at times shows a complex adsorption isotherm (2). Earlier work (5,6) has also shown that anionic surfactants adsorb on polyvinyl acetate, then slowly penetrate into the particle leading to the formation of a poly-electroyte type solubilized polymer-surfactant complex. Such a solubilization process is generally accompanied by an increase in viscosity. The first objective of this work is to better under-stand the effects of type and structure of surfactants on the solubilization phenomena in vinyl acetate and vinyl acetate-butyl acrylate copolymer latexes. 

Latex thickening in the presence of penetrating type anionic surfactants such as NaLS appears to depend on polymer composition as seen in Table III. The extent of latex thickening in the presence of excess NaLS decreases with the VA content of a vinyl acetate-butyl acrylate copolymer. Polystyrene and poly acrylate copolymer latexes do not show any thickening. 

Differential scanning calorimetry (DSC) was used to determine the kinetics of polymerization and the glass transition temperature of the solid polymer. Preliminary results indicate the dependence of kinetics on the microstructure as determined using Borchardt and Daniels method (26). The reaction order, rate constant, and conversion were observed to be dependent on the initial microstructure of the microemulsions. The apparent glass transition temperature (Tg) of polystyrene obtained from anionic surfactant (SDS) microemulsions is significantly higher than the Tg of normal bulk polystyrene. In contrast, polymers from nonionic microemulsions show a decrease in Tg. Some representative values of Tg are shown in Table I. 

The curves obtained at various concentrations are almost parallel. This observation means that the rate of change of voltage with respect to temperature is independent of the solids concentration. By cross-plotting the results shown in Figure 24, a set of calibration curves can be prepared with temperature as a parameter. When such curves were prepared, they indicated that the value of e at C = 0, obtained by extrapolation, was lower than the corresponding value obtained for tap water at the same temperature. A review of the procedure of this experiment indicated that the only possible reason for this difference was the fact that a small amount of a wetting agent (an anionic surfactant) was added with the solids to increase the wettability of the polystyrene particles. 

Alkylphenols, nitrophenols, halogenophenols and polyhydroxybenzenes have been extensively studied on a thin layer of anion and cation exchangers with cellulose, paraffin, and polystyrene matrices and on silanized silica gel impregnated with anionic and cationic surfactants. The best results have been obtained by using cation exchangers and anionic surfactants as impregnating agents [4,5]. 

Swelling of polystyrene latex particles with styrene. The swelling ratios and the corresponding interfacial tensions for the different-size latexes with added anionic surfactants Aerosol MA and sodium dodecyl sulfate are listed in Table II. Those values obtained with added nonionic surfactant Triton X-100 and polymeric surfactant polyvinyl pyrrolidone are listed in Table III. Figure 1 compares theoretical curves from Model I with all of the experimental data. It is found that a curve corresponding to Xmp = 0.35 fits the data best. Therefore, a semi-empirical... 

The polyethylene latexes obtained in the different emulsion polymerization procedures using the various aforementioned nickel(II) complexes display average particle diameters of 100 to 600 nm. A number of anionic surfactants or neutral stabilizers are suitable, i.e. compatible with the catalysts and capable of stabilizing the latex. Solids contents of up to 30% have been reported to date. A typical TEM image is shown in Fig. 7.2. By comparison to smooth, spherical latex particles of amorphous polystyrene as a well studied hydrocarbon polymer prepared by free-radical emulsion polymerization, the ruggedness of the particles shown can be rationalized by their high degree of crystallinity. 

Very recently, an aqueous olefin polymerization using an early transition metal catalyst has also been reported [84]. A toluene solution of styrene is prepolymerized briefly by a catalyst prepared by combination of [(CsMesjTifOMe),] with a borate and an aluminum-alkyl as activators. The reaction mixture is then emulsified in water, where further polymerization occurs to form syndiotactic polystyrene stereoselectively. It is assumed that the catalyst is contained in emulsified droplets and is thus protected from water, with the formation of crystalline polymer enhancing this effect. Cationic or neutral surfactants were found to be suitable, whereas anionic surfactants deactivated the catalyst. The crystalline polystyrene formed was reported to precipitate from the reaction mixture as relatively large particles (500 pm). 

In the field of nonionic polymerizable surfactants, a pioneering work was published by the Ottewill group. They prepared two sets of polystyrene latexes [29]. The first set was initiated by KPS at 80 °C and resulted in charged latexes. The set comprised a conventional anionic surfactant, a conventional nonionic... 

The anionic surfactant SDS affected the dye sorption in three ways no impact on the dyes uptake, decrease in the dyes uptake or enhanced dyes uptake as shown in Figure 9. The first mentioned behavior was observed during the sorption of C.I. Acid Orange 7 (100 mg/L) from the solutions containing 0.1-2 g/L SDS not only for the polystyrene anion exchangers but also for the polyacryUc ones (Figure 9 a) and b)). 

Figure 9. Influence of anionic surfactant sodium dodecyl sulfate (SDS) on uptake of C.I. Add Orange 7 by the polystyrene anion exchangers (a) as well as the polyacryUc and phenol-formaldehyde anion exchangers (b), of C.I. Reactive Black 5 by the polystyrene ardon exchangers (c) as well as the polyacrylic and phenol-formaldehyde anion exchangers (d) and of C.I. Direct Blue 71 by the polystyrene anion exchangers (e) as well as the polyacrylic and phenol-formaldehyde anion exchangers (f)...

Fig. 16.9. The dependence of the critical concentration of free hydroxyethyl cellulose upon its molecular weight for the depletion flocculation of polystyrene latex particles curves 1, in the absence of anionic surfactant 2, in the presence of nonionic surfactant (after Sperry et al., 1981).

Qutubuddin and coworkers [43,44] were the first to report on the preparation of solid porous materials by polymerization of styrene in Winsor I, II, and III microemulsions stabilized by an anionic surfactant (SDS) and 2-pentanol or by nonionic surfactants. The porosity of materials obtained in the middle phase was greater than that obtained with either oil-continuous or water-continuous microemulsions. This is related to the structure of middle-phase microemulsions, which consist of oily and aqueous bicontinuous interconnected domains. A major difficulty encountered during the thermal polymerization was phase separation. A solid, opaque polymer was obtained in the middle with excess phases at the top (essentially 2-pentanol) and bottom (94% water). The nature of the surfactant had a profound effect on the mechanical properties of polymers. The polymers formed from nonionic microemulsions were ductile and nonconductive and exhibited a glass transition temperature lower than that of normal polystyrene. The polymers formed from anionic microemulsions were brittle and conductive and exhibited a higher Tj,. This was attributed to strong ionic interactions between polystyrene and SDS. 

Figure 6.2. Simultaneous adsorption of a nonionic surfactant, a nonylphenol ethoxylate (NP-EOio) and an anionic surfactant, sodium dodecyl sulfate (SDS), on polystyrene latex. (From B. Jonsson et ai. Surfactants and Polymers in Aqueous Solution, John Wiley, Chichester, 1998, p. 291, Reproduced with permission)...

Eventually, it was reported that it was possible to prepare a very concentrated (up to 40 wt%) uniform polystyrene nanoparticles (down to 60 nm) in the presence of only 1.82 wt% of anionic surfactant, sodium dodecyl sulfate [41 ], if micro-wave irradiation was applied. 

Figure 9.4(a) Zeta potential as a function of the logarithm of the concentration of anionic surfactants adsorbed on to polystyrene latex sodium tetradecyl sulphate, NaDS, and O sodium decyl sulphate. The CMC for NaDS in water is shown by the arrow, (b) Shows... 

Surfactants — either anionic surfactants such as sodium dodecylsulfate [SDS], or sodium dodecyl benzene sulfate [SDBS], or polysaccharide [Gum Arabic GA] — were first used to disperse, and exfoliate as-produced SWCNTs in water by ultrasonication, and to stabilize the resulting aqueous CNT suspension, see Figure 2.12. The SWCNTs were synthesized by either the AD method [about 30 % of impurities], or by the HiPCO process [having a catalyst particle content of about 5 wt%]. Please note that not only short surfactant molecules, but also polymeric surfactants such as polystyrene sulfonate, or even conductive polymers having a surfactant nature, can also be successfully used to disperse CNTs in water. 

It is noteworthy that a basic assumption made in the derivation of the free radical desorption rate constant is that the adsorbed layer of surfactant or stabilizer surrounding the particle does not act as a barrier against the molecular diffusion of free radicals out of the particle. Nevertheless, a significant reduction (one order of magnitude) in the free radical desorption rate constant can happen in the emulsion polymerization of styrene stabilized by a polymeric surfactant [42]. This can be attributed to the steric barrier established by the adsorbed polymeric surfactant molecules on the particle surface, which retards the desorption of free radicals out of the particle. Coen et al. [70] studied the reaction kinetics of the seeded emulsion polymerization of styrene. The polystyrene seed latex particles were stabilized by the anionic random copolymer of styrene and acrylic acid. For reference, the polystyrene seed latex particles stabilized by a conventional anionic surfactant were also included in this study. The electrosteric effect of the latex particle surface layer containing the polyelectrolyte is the greatly reduced rate of desorption of free radicals out of the particle as compared to the counterpart associated with a simple... 

We would like to stabilize polystyrene (PS) particles by using either the NPE15 surfactant or the classical SDS (sodium dodecyl sulfate) anionic surfactant. Which surfactant would you use and why (Use the HLB-CPP plot of Problem 7.6.)... 

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