Phase polyoxyethylene alkyl

Phase diagrams of water, hydrocarbon, and nonionic surfactants (polyoxyethylene alkyl ethers) are presented, and their general features are related to the PIT value or HLB temperature. The pronounced solubilization changes in the isotropic liquid phases which have been observed in the HLB temperature range were limited to the association of the surfactant into micelles. The solubility of water in a liquid surfactant and the regions of liquid crystals obtained from water-surfactant interaction varied only slightly in the HLB temperature range. 

The behavior of a series of polyoxyethylene alkyl ether nonionic surfactants is also illustrative. According to Figure 11 the dioxyethylene (A) compound does not form liquid crystals when combined with water. Its solutions with decane dissolve water only in proportion to the amount of emulsifier. The tetraoxyethylene dodecyl ether (B) forms a lamellar liquid crystalline phase and is not soluble in water but is completely miscible with the hydrocarbon. The octaoxyethylene compound (C) is soluble in both water and in hydrocarbon and gives rise to three different liquid crystals a middle phase, an isotropic liquid crystal, and a lamellar phase containing less water. If the hydrocarbon p-xylene is replaced by hexadecane (D), a surfactant phase (L) and a lamellar phase containing higher amounts of hydrocarbon are formed in combination with the tetraoxyethylene compound (B-D). 

A combination of SLS and DLS methods was used to investigate the behavior of nonionic micellar solutions in the vicinity of their cloud point. It had been known for many years that at a high temperature the micellar solutions of polyoxyethylene-alkyl ether surfactants (QEOm) separate into two isotropic phases. The solutions become opalescent with the approach of the cloud point, and several different explanations of this phenomenon were proposed. Corti and Degiorgio measured the temperature dependence of D pp and (Ig), and found that they can be described as a result of critical phase separation, connected with intermicellar attraction and long-range fluctuations in the local micellar concentration. Far from the cloud point, the micelles of nonionic surfactants with a large number of ethoxy-groups (m 30) may behave as hard spheres. ... 

In 1980, Yoshimura et al. [24] reported a fluid-solid phase separation in a mixture of polystyrene latex (cri = 510nm) and the non-ionic surfactant polyoxyethylene alkyl phenylether at KCl concentrations above 0.05 mole/1. At a surfactant... 

Zech et al. [90] reported high-temperatiue-stable microemttlsions composed of the room-temperature IL EAN as polar phase. Byrne et al. [91] reported on the solubility of HEWL in aqueous EAN as a function of water content. The structure of micelles formed by nonionic polyoxyethylene alkyl ether nonionic surfactants in the room-temperatrrre IL EAN by small-angle neutron scattering as a function of alkyl and ethoxy chain length, concentration, and temperatrrre, was reported by Araos et al. [92]. 

The increase in spontaneous curvature at a given concentration with increasing length of the hydrophihc chain is clear as the number of units increases from 3 to 50 [13,16,19]. The cubic phases for 20 35 oxyethylene units are located between the miceUar and the hexagonal phases, which implies micellar cubic phases. It can be noted that the temperature stability of the liquid crystalline phases for sterol surfactants with 20 and 30 polyoxyethylene units is remarkably high compared with those formed by polyoxyethylene alkyl surfactants (see Fig. 4c, d) [16]. 

Structured W/O systems similar to those obtained in O/W systems have been reported in which the oil phase consists of liquid paraffin and a microcrystalline wax, the emulsifier being a polyoxyethylene alkyl ether [125] alerting us to the potential complexities of inverse emulsions. 

Aughel and coworkers [63] studied the phase behavior of hydrocarbon-water mixtures in the presence of alkyl(aryl)polyoxyethylene carboxylates for enhanced oil recovery and found good salt tolerance with an alkyl ether carboxy-late (C13-C15) with 7 mol EO and a good microemulsion forming effect with the 3 EO type. 

Nonionic surfactants such as polyoxyethylated fatty alcohols (such as Emul-phor ON-870 from GAP), alkyl phenyl polyethylene glycol ethers (such as the Tergitols from Union Carbide) and polyoxyethylated octylphenol may be used as protective colloids along with anionic surfactants or, in some cases, as emulsifiers in their own right. The block copolymers of polyoxyethylene and polyoxypropylene (Pluronics) solubilized vinyl acetate. Polymerization takes place at the interface of the surfactant-monomer droplet and the aqueous phase [151]. 

Commercial polyoxyethylene surfactants contain a wide range of EO sizes, often with a reasonably defined alkyl chain. Bouwstra et al. [116] studied a commercial sample of Cg=C9EOi4 (i.e. a Cig chain with 9-10 cis double bond and a polydisperse EO group). It exhibits phase behavior similar to C12EOg... 

Commercial polyoxyethylene surfactants contain a wide range of EO sizes, often with a reasonably defined alkyl chain. Bouwstra and co-workers (130) have studied a commercial sample of Cq CqEOh (i.e. a Cig chain with 9-10 cis double bonds and a polydisperse EO group). The latter exhibits phase behaviour similar to C12EO8, with Ii, Hi, Vi and L phases. The Hi phase exits between 35.6 and 74.8 wt% surfactant and up to 84°C. The other phases exist over narrower concentration ranges and to lower temperatures. Similar studies have also been reported by Kunieda and co-workers (131, 132) for a wide range of commercial oleoyl EO derivatives again, the commercial actives behave like pure ones with a shorter EO size. 

The adsorption of anionic, cationic and non-ionic surfactants on to hydrophilic and hydrophobic surfaces in aqueous continuous phases has been considered in Chapter 1. Adsorption of surfactants on to non-polar surfaces occurs via hydrophobic interactions, the hydrocarbon chain adsorbing and lying close to the solid surface adsorption on to polar surfaces can occur by specific electrostatic interactions in which the surface is converted from a hydrophilic surface to a hydrophobic surface by the orientation of the alkyl chains of the surfactants outward into the water (Fig. 9.3). Adsorption of surfactants in this way frequently gives rise to multilayer adsorption by hydrophobic interactions between the primary and secondary monolayers, as shown in Fig. 9.3. Non-ionic surfactants based on polyoxyethylene ethers may also adsorb on to hydrophilic surfaces such as silica in this way. A representation of the orientation of non-ionic surfactants at a silica surface is shown in Fig. 9.3b. Adsorption isotherms for polar and nonpolar systems reflect these different possibilities as has been discussed previously (section 1.4). 

Figure 9.3(a) shows the mode of adsorption of an ionic surfactant at a hydrophilic surface, with its polar head groups close to the surface and non-polar chains pointing out into the aqueous phase. As one proceeds down the diagram, the bulk solution concentration of the surfactant is being increased until bilayers are formed by hydro-phobic associations of the alkyl chains of the surfactant, rendering the surface hydrophilic, (b) shows the possible mode of association of non-ionic alkyl polyoxyethylene ethers at a hydrophilic silica surface at a concentration where bilayers are forming. From Rupprecht [6] with permission. 

Masukawa and Tsujimura (1997) patented a method to determine surfactants in cosmetic products by reversed-phase LC without pre-treatment. Chromatographic conditions involved a binary gradient with methanol and water, ammonium carbonate salt as buffer and LSD detection. Amphoteric surfactants (Cg-Ci6 amidobetaines), an anionic surfactant (Cl2-16 acylmethyltaurine) and two types of nonionic surfactants (Cg i4 diethanolamides and Ci2 14 alkyl polyoxyethylene alcohols) were identified on applying this method. 

---