The Characteristic Curvature of Ionic Surfactants

Abstract

Characterizing the hydrophilic-lipophilic nature of a surfactant molecule has been a challenge for colloid scientists and technologists. The hydrophilic-lipophilic balance (HLB), the packing factor, the phase inversion temperature (PIT) and the natural curvature of the surfactant are all terms that seek to address this issue. In this article we build on the hydrophilic-lipophilic difference concept (HLD) (Salager et al. Langmuir, 16, 5534-5539, 2000) to develop a methodology to determine a characteristic curvature (Cc) for ionic surfactants based on the phase behavior of mixed ionic surfactant microemulsions. In essence, the method consists of evaluating the shift in optimal electrolyte concentration as a function of the mole fraction of the test surfactant in a mixture with a reference surfactant, sodium dihexyl sulfosuccinate (SDHS) and applying the appropriate HLD equation for ionic surfactant mixtures to determine Cc. The values of Cc were determined for a range of surfactants, including sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS), sodium naphthenate, and others. The method was also extrapolated to nonionic additives and hydrophilic linkers. It was observed that the calculated values of Cc were similar to those predicted by group contribution models, however the proposed method can be used even for complex surfactant mixtures. Finally, when Cc values were compared to apparent packing factor and HLB values, it was found that Cc is correlated with the apparent packing factor of ionic surfactants, and that Cc correlates with the HLB value for nonionic amphiphiles.The physical interpretation of Cc, and its potential application in the Net-Average Curvature equation of state for oil-surfactant-water systems is discussed.

Next Generation Surfactants for Improved Chemical Flooding Technology

“…The method used in conducting the salinity scans for the purpose of determining Cc values was described by Acosta et al [2008]. In this method the surfactant AMA is used as the reference surfactant and is designated as S 1 .in equations (1) and (2).…”

“…Characteristic curvature (Cc) values of the surfactants were used to predict the optimal salinities (S) of binary systems using the form of the HLD equation shown in equation 2-5 [Acosta et al 2008]. Since the reservoir temperatures are not 25 °C, temperature effects must be taken into account.…”

“…The use of the HLD equation takes into consideration the relative hydrophobic balance of the surfactant mixture in the solution, in order to calculate its optimal formulation, this is, a zero value for the HLD. According to Acosta et al 2008 method, this optimum would correspond to an equal water and oil solubility for the surfactant system, and therefore, a near net zero-curvature for the bi-continuous microemulsion (Type III or IV).…”

“…The HLD relation for a mixture of two anionic surfactants at 25°C without alcohol described by Acosta [2008] was used in this project and is shown below in equation (1-1).…”

Equivalent Alkane Carbon Number of Live Crude Oil: A Predictive Model Based on Thermodynamics

“…where f(A) is related to alcohol amount and type, T ref equals 298.15 K, a is a temperature coefficient, Cc -the characteristic curvature -reflects the tendency of the surfactant to form micelles or reverse micelles [8,9], and K is a parameter related to the formulation chemistry (i.e. chemistry of surfactants, types of salts, TDS -the amount of total dissolved solids -etc.).…”