Interfacial Tension and Behavior of Nonionic Surfactants
Authors: Hayes Michael E. , Bourrel Maurice , El-Emary Mahmoud M. , Schechter Robert S. , Wade William H. 
Published: December 2007

Low interfacial tensions are possible with nonionic surfactants. The effects of several solution variables (e.g., salinity and alcohol) on low-tension behavior have been determined for some nonionic surfactants. Nonionics have been found to be much less sensitive to changes in solution conditions than anionics (sulfonates) studied to date.

Introduction

A survey of the literature reveals very few examples of low interfacial tension (IFT) with nonionic surfactants and few systematic studies of the IFT behavior of nonionics. Youngs examined the tension behavior of some aminimides; Shinoda et al. investigated the emulsion phase-inversion temperatures of ethoxylated nonionic surfactants and stated that the IFT between the oil and aqueous phases approaches zero at the phase-inversion phases approaches zero at the phase-inversion temperatures.It has been shown that it is possible to achieve ultralow; (10 dyne/cm) IFT's using pure hydrocarbons as the oil phase. Subsequent work has proved the feasibility of attaining low IFT's between pure hydrocarbons and pure alkylbenzene sulfonates. In this paper, nonionic surfactants are similarly shown to be capable of giving IFT'S. Further, the low-tension state is associated with the three-phase (microemulsion) region of the ternary phase diagram, but the presence of a "middle" phase is not a sufficient condition for low IFT's.The effects of several solution variables on low IFT behavior have been determined for some nonionic surfactants. Comparison of these results with those of similar studies of anionics (sulfonates) shows that nonionics' behavior is (1) much less sensitive to hydrophobe structure; (2) less sensitive to salinity changes; (3) more tolerant to divalent cations (i.e., Ca+ +); (4) less dependent on alcohol concentration; and that (5) for some nonionics, pH can be an important factor.Obviously, the first four of these could be of considerable significance from a practical standpoint, as they all represent improvement over the behavior usually exhibited by sulfonate surfactants.

Materials and Experiment

The ethoxylated aliphatic primary alcohols and the five ethoxylated dinol phenols (DNP) are commercial samples provided by Witco Chemical Corp. These samples are described in Table 1. Witco also supplied a commercial coconut diethanolamide [R-CON(CH CH OH), R C,]. Other alkyl variants of the diethanolamides were synthesized in this laboratory.The ethoxylated nonylphenols (IGEPAL CO) were supplied by GAF Corp. and were 100% active materials. We had at our disposal products with 4, 6, 7.5, 9, and 10.5 moles of ethylene oxide per mole of hydrophobe - IGEPAL CO430, CO530, CO610, CO630, and CO710, respectively. To obtain products containing intermediate values of ethylene oxide, mole-fraction weighted mixtures of these materials were prepared.The Klearfac AA-270 phosphate ester was provided by BASF Wyandotte. Steven McGuire of provided by BASF Wyandotte. Steven McGuire of Conoco Inc. ethoxylated samples of 6-undecanol and 7-tridecanol prepared in this laboratory. DNP-M1 is an experimental ethoxylated dinonyl phenol of somewhat narrowed molecular weight distribution provided by Milliken Chemical Co. provided by Milliken Chemical Co. SPEJ

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