Phase Behavior and Microstructure of Symmetric Nonionic Microemulsions with Long-Chainn-Alkanes and Waxes

Abstract

Microemulsions are thermodynamically stable, macroscopically isotropic mixtures of at least two immiscible components and a surfactant. Their general features, i.e. the complex phase behavior, the ultralow interfacial tensions, and the multifarious nanostructure, have been systematically elucidated in the last century. However, the efficient solubilization of long-chain n-alkanes and waxes, which plays a significant role in enhanced oil recovery, washing, and cosmetics, remains a challenge. Thus, in this work the influence of the n-alkane chain length k on the phase behavior of ternary (symmetric) microemulsions containing equal volumes of water and oil was studied. Using n-alkanes ranging from n-dodecane (C 12 H 26 ) to n-dotriacontane (C 32 H 66 ) and pure n-alkyl polyglycol ether (C i E j ) surfactants, we found that the efficiency of the respective surfactant decreases linearly with increasing k, while the phase inversion temperature (PIT) shows a logarithmic dependence. The influence of a technical wax on the phase behavior was studied by means of the systems H 2 O−SASOLWAX 5805 (Sasol)−C 16 E 6 yielding an equivalent alkane carbon number (EACN (SASOLWAX 5805)) of 30.8. Finally, the pure C i E j surfactants were replaced with technical grade counterparts of the Genapol series (Clariant) finding that the solubilization efficiency of the long-chain Genapol O 080 is comparable to the pure C 16 E 6 surfactant. Using small-angle neutron scattering (SANS) the microstructure of the formulated microemulsions was studied near the so-called optimum (X ̃) point. The scattering curves prove that microemulsions containing long-chain n-alkanes and waxes are also bicontinuously structured at the phase inversion temperature (PIT). Interestingly, a high degree of structural ordering is found reflected by values of the amphiphilicity factor f a ranging between −0.83 and −0.87.

Efficiency Boosting of Surfactants with Poly(ethylene oxide)-Poly(alkyl glycidyl ether)s: A New Class of Amphiphilic Polymers

“…2,3,65 Very recently, it was shown that symmetric microemulsions containing pure long-chain oils (e.g., n-octacosane) or even technical-grade waxes (e.g., Sasolwax 5805) can be formulated using on the order of 15 wt % pure and technical-grade non- ionic n-alkyl polyglycol ether type surfactants. 44,66 However, in order to decrease the environmental impact of surfactants and the overall costs, a considerable reduction of the amount of surfactant needed to form microemulsions is highly desirable. This was our motivation to study whether the new PEO-b-PAlkGE copolymers can also be used to increase the efficiency of long-chain surfactants to formulate microemulsions containing long-chain oils or even technical-grade waxes.…”

“…Based on a very recent study of Sasolwax 5805-containing microemulsions stabilized by technical-grade surfactants of the Genapol type, 44 we formulated a symmetric (ϕ = 0.500) microemulsion of the type H 2 O/NaCl (ε = 0.001)−Sasolwax 5805−Genapol O 050/O 080, starting with a 1:1 (m/m) mixture of the two Genapol surfactants. The phase behavior of this polymer-free technical grade microemulsion system is shown in Figure 6 in the form of a T(γ) section (blue circle).…”

“…The procedure for the investigation of the phase behavior of nonionic microemulsion systems can be found elsewhere. 44 Here, we will only focus on the most important procedures for the water/NaCl (A)−oil (B)−nonionic surfactant (C)/amphiphilic diblock copolymer (D) systems studied in this work. For sample preparation, all components are weighed in test tubes with an accuracy of Δm = ± 0.001 g, starting with the amphiphilic diblock copolymer (smallest amount) and the surfactant(s) followed by the respective oil, which are known to be good solvents for nonionic surfactants.…”

“…Thus, in a first step, we studied the effect of Me-P­(EO) 113 - b -P­(C 12 GE) 7 on the phase behavior and microstructure of the model microemulsion system H 2 O/NaCl– n -decane–C 10 E 4 . For technical applications, such as enhanced oil recovery, efficient solubilization of long-chain n -alkanes is of interest, which is why we investigated the extent of boosting of PEO- b -PAlkGE polymers in H 2 O/NaCl– n -octacosane–C 16 E 6 microemulsions in the next step. By means of this microemulsion system, the effect of varying both the alkyl chain length and the number of repeating units of the alkyl glycidyl ether block was studied.…”

Nanoemulsion Based Vehicle for Effective Ocular Delivery of Moxifloxacin Using Experimental Design and Pharmacokinetic Study in Rabbits

“…From the phase diagram, it was indicated that the change in phase behavior within the nanoemulsion region is mainly due to the hydrophobic carbon chain length of the oil and the ratio between surfactant and cosurfactant mixture used in the formulation. Therefore, it is likely that the hydrocarbon chain length compatibility among surfactant and oil is an important factor that affects the globule size formation and stability of nanoemulsion as suggested by Schneider et al [29].…”