Anionic-nonionic surfactant systems discussed

In the remainder of this article, discussion of surfactant dissolution mechanisms and rates proceeds from the simplest case of pure nonionic surfactants to nonionic surfactant mixtures, mixtures of nonionics with anionics, and finally to development of myehnic figures during dissolution, with emphasis on studies in one anionic surfactant/water system. Not considered here are studies of rates of transformation between individual phases or aggregate structures in surfactant systems, e.g., between micelles and vesicles. Reviews of these phenomena, which include some of the information summarized below, have been given elsewhere [7,15,29]. 

In this paper, we report the solution properties of sodium dodecyl sulfate (SDS)-alkyl poly(oxyethylene) ether (CjjPOEjj) mixed systems with addition of azo oil dyes (4-NH2, 4-OH). The 4-NH2 dye interacts with anionic surfactants such as SDS (11,12), while 4-OH dye Interacts with nonionic surfactants such as C jPOEn (13). However, 4-NH2 is dependent on the molecular characteristics of the nonionic surfactant in the anlonlc-nonlonic mixed surfactant systems, while in the case of 4-OH, the fading phenomena of the dye is observed in the solubilized solution. This fading rate is dependent on the molecular characteristics of nonionic surfactant as well as mixed micelle formation. We discuss the differences in solution properles of azo oil dyes in the different mixed surfactant systems. 

Kunieda s group reported numerous viscoelastic worm-like micellar systems in the salt-free condition when a lipophilic nonionic surfactant such as short hydrophilic chain poly(oxyethylene) alkyl ether, C EOni, or N-hydroxyethyl-N-methylaUcanolamide, NMEA-n, was added to the dilute micellar solution of hydrophilic cationic (dodecyltrimethylammonium bromide, DTAB and hexade-cyltrimethylammonium bromide, CTAB) [12-14], anionic (sodium dodecyl sulfate, SDS [15, 16], sodium dodecyl trioxyethylene sulfate, SDES [17], and Gemini-type [18]) or nonionic (sucrose alkanoates, C SE [9, 19], polyoxyethylene cholesteryl ethers, ChEO [10, 20], polyoxyethylene phytosterol, PhyEO [11, 21] and polyoxyethylene sorbitan monooleate, Tween-80 [22]) surfactants. The mechanism of formation of these worm-Hke stmctures and the resulting rheological behavior of micellar solutions is discussed in this section based in some actual published and unpublished results, but conclusions can qualitatively be extended to aU the systems studied by Kunieda s group. 

The interaction between ionic polymers and nonionic surfactants has not received as much attention as the other cases discussed in the preceding sections. Much of the earlier research in this area has been focused on the interaction of anionic polymeric acids with nonionic surfactants of polyethylene oxide. The polyethylene oxide has shown the ability to form hydrogen bonds with polymeric acid like polycarboxylic acid in water. This canses a redaction in the solution viscosity as the polymer chains tend to shrink. Saito and Taniguchi (1973) studied the interaction of polyacrylic acid with a series of nonionic surfactants (EO) RE in which EO is ethylene oxide, R is hydrocarbon group, and E represents ether. They reported that the interaction in this system is a function of the nature of the hydrophobic moiety (R) and the length of the hydrophilic tail (EO). 

In the present study, hydrophobic interaction between hydroxypropylcellulose (HPC) and an ionic surfactant in an aqueous phase was discussed. HPC, as well as EHEC, is a nonionic cellulose ether which contains hydrophobic groups in its molecular structure. Therefore, it might be interesting to compare the complex-formation properties of HPC with that of EHEC. The surfactants used here were an anionic surfactant SDS and a cationic one cetylpyridinium chloride (CPC). HPC formed a complex with these surfactants, of which cloud point changed with the surfactant concentration in the same manner as that observed in the EHEC-surfactant systems [4]. Effects of the complex on stability of dilute and concentrated kaoiinite suspensions were also studied, taking physicochemical properties of the complex into account. 

In considering the structure of micelles, we continue to base our discussion on aqueous, anionic surfactant solutions as prototypes of amphipathic systems. Cationic micelles are structured no differently from anionics, and nonionics are described parenthetically at appropriate places in the discussion. We summarize present thinking about the structure of micelles at surfactant concentrations equal to or only slightly above the CMC. We see that in nonaqueous systems (Section 8.8) and in concentrated aqueous systems (Section 8.6), the surfactant molecules are organized quite differently from the structure we describe here. 

Surfactants are particularly suitable as additives for the control of crystallization because of their specific molecular stracture. A surfactant molecule consists of an ionic or nonionic hydrophillic headgroup coupled with a hydrophobic tail. In a crystallization system the headgroup binds to the crystal surface while the tail provides steric hindrance for the incorporation of growth units into the crystal lattice. As surfactants are relatively inexpensive and readily available in many different designs, they should be regarded as ideal crystallization modifiers for industrial applications. The ability of anionic surfactants to control nucleation from solutions supersaturated with different calcium oxalate hydrates will be discussed in some detail. 

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